Search

These experiments test the hypothesis that cells carrying the Ly1+23- surface phenotype are programmed exclusively for helper and not suppressive activity regardless of external conditions such as the mode or type of antigen stimulation. To this end, we have stimulated purified populations of Ly1 cells with antigen in vitro using conditions devised to induce unselected T cells to express optimal levels of antigen specific T-suppressor activity. We find that after such stimulation, Ly1 cells generate SRBC-specific T-helper activity but not T-suppressive activity. These findings establish that the Ly1.2+,2.2/3.2- surface phenotype is a stable, and probably invariant, marker of T cells that are programmed to express only helper activity and have lost the capacity to directly suppress the antibody response. These findings support the concept that the genetic program for a single differentiated set of cells combines information for cell surface phenotype and function. We also demonstrate that antigen-stimulated Ly1 cells, in addition to inducing B cells to secrete antibody, can induce or activate other sets of resting T cells to develop profound suppressive effects. The surface phenotype of this feedback suppressive T-cell set is shown to be: Ly1+2+3+Qa1+. These findings, taken together, indicate that activation of resting Ly123 cells by immune Ly1 TH cells may represent an important homeostatic immunoregulatory mechanism.

Mice immunized with more SRBC than are required to produce optimal delayed-type hypersensitivity reactions, developed good antibody responses and poor delayed foot pad reactions. Cyclophosphamide treatment in low doses (20 mg/kg) before immunization, augmented the delayed-type hypersensitivity without affecting antibody responses. Cyclophosphamide did not augment delayed responses to optimal doses of SRBC (0.01%), but did augment the delayed hypersensitivity response of mice immunized with a suboptimal antigen dose (0.001%); which produced no detectable antibody response with or without cyclophosphamide pretreatment. These results suggest that antibody feedback is not the sole regulator of delayed reactions; the possibility that suppressor T cells may also be involved is discussed.

Spleen cells educated in vitro with sheep red blood cells (SRBC) suppressed the plaque-forming cell response of Mishell-Dutton assay cultures challenged with optimal doses of SRBC. Changing conditions in the assay cultures changed the effect educated cells had on the assay culture responses. For example, educated cells helped rather than suppressed assay cultures of suboptimal numbers of spleen cells. Similarly, augmentation resulted upon addition of educated cells to assay cultures challenged with suboptimal doses of SRBC. Such a reversal of regulatory effects was not observed when assay cultures were challenged with supraoptimal antigen doses. Educated cells helped assay cultures of B spleen cells, and the addition of normal T cells reinstated suppression. Furthermore, maintenance of assay cultures under stationary rather than the usual rocking conditions allowed educated cells to help rather than suppress the antibody response of assay cultures. These results show that when the response of the target population (assay cultures) is low, the regulator (educated) cells augment the response, and vice versa, supporting the hypothesis that the effect regulator cells produce depends on the activity of the cells they regulate.

A bone-resorbing factor, comparable to the osteoclast-activating factor (OAF) produced from peripheral blood leukocytes, is shown to be produced by murine spleen cells activated with the T-cell mitogen Con A. Murine OAF is demonstrated here as being a product of the interaction between thymus-derived T lymphocytes and macrophages. Activation of T cells in the presence of macrophages with Con A yields culture supernatants with OAF activity. This OAF activity is not dialyzable and is not extracted by lipid solvents. Purified B cells in the presence or absence of macrophages and cocultured with Con A or activated with the B-cell-specific mitogen lipopolysaccharide yield culture supernatants with no detectable OAF activity. Similarly, macrophages cocultured with Con A or activated with lipopolysaccharide fail to yield culture supernatants with bone resorbing activity. These types of immune cell interactions are similar to that required for the production of lymphokines. These data support the hypothesis that one aspect of regulation of bone remodeling is through cells of the immune system.

The biologically active mediators of antigen-specific T suppressor cells can combine with antigen on cells that are specialized to present antigen (APC) and render these APC incapable of presenting not only the specific antigen that the product of the T suppressor cell sees but also any other antigen in or on the APC. Thus, antigen-bearing suppressed APC fail to activate either the helper or suppressor system involved in the regulation of contact sensitivity responses. These results demonstrate that APC are targets of T suppressor cells. They also imply that a metabolic event is required for functional antigen presentation and that T suppressor cells can block that metabolic pathway.

The fact that T cell-dependent activation of mast cells occurs in delayed-type hypersensitivity led us to investigate whether a T cell product could mimic some of the functions of IgE. We report that 24- or 48-hr cultures of T cells from mice immunized optimally for delayed-type hypersensitivity resulted in release of an antigen-binding factor that transferred the ability to elicit an antigen-specific immediate hypersensitivity-like skin reaction in normal recipients. The responsible factor was concentrated and purified by affinity chromatography on antigen columns and was distinguished from immunoglobulin by several criteria: (i) it was released by purified T cells (anti-immunoglobulin plate depletion of B cells); (ii) it expressed no known antigenic markers of immunoglobulins (enzyme-linked immunosorbant direct binding assay); (iii) it had a molecular weight of 70,000 or less (sucrose gradient ultracentrifugation); and (iv) it had serological markers associated with antigen-specific T cell factors from other experimental systems. We suggest that, at sites of delayed-type hypersensitivity, antigen-reactive T cells may release antigen-specific factors that lead to mast cell activation and release of vasoactive amines, which is required for elicitation for these responses.

We have asked the question: how do partner cells in immunoregulatory interactions between T cell subsets acquire the ability to recognize and react appropriately with one another? In particular, we have asked whether these communication events are completely determined by the cell's genetic constitution, or whether the recognition events can be learned during ontogeny. We have found that the T cells of parent into F1 chimeras and homozygous nude mice with F1 thymus grafts not only learn to react with genetically disparate acceptor cells, but that the receptors on the acceptor cells themselves learn to react with genetically disparate producer cells. This learning process can overcome both major histocompatibility complex- and immunoglobulin heavy chain variable region-linked restricted communication between T cell subsets. We interpret these findings to indicate that thymic elements can start a cascade of differential events. The thymic elements, whether endogenous or passively acquired, select from a pool of producer cells those that will react appropriately with the thymic selecting cells, and these cells become expanded. Then, the private markers (idiotype) on the expanded pool of producer cells act as selecting and expanding elements that choose from a pool of acceptor cells those that recognize the producer cells idiotype as self. This second differentiational event, although apparently thymus evidence that this type of acceptor cell differentiation could also take place during the course of an immune response.

We have previously suggested that the release of serotonin (5-hydroxytryptamine) (5-HT) by local tissue mast cells is required for the elicitation of delayed-type hypersensitivity (DTH) in mice. In the current study, light microscopic radioautographs from animals treated with [3H]5-HT indicated that local mast cells released 5-HT between 6 and 18 h during the evolution of DTH. Ultrastructural examination of mast cells revealed surface activation, indicated by extension of surface filopodia, and degranulation by fusion and exocytosis. Light and electron microscopic studies of the endothelium of postcapillary venules at sites of DTH revealed the development of gaps between adjacent cells. The development of gaps permitted extravasation of tracers that was abolished by depletion or antagonism of 5-HT. Thus mast cells degranulated and released 5-HT in DTH, and this 5-HT acted on local vessels. Recipients of nonadherent, non-immunoglobulin-bearing sensitized lymphocytes also demonstrated similar mast cell degranulation and the formation of endothelial gaps. This indicated that mast cell degranulation and 5-HT release in murine DTH were probably T cell dependent.

Shortly after intravenous immunization of mice with heterologous erythrocytes (RBC) antigen-specific Thy 1+ cells which form rosettes with the immunizing RBC (thymic-derived lymphocytes-forming rosettes [T-RFC]) appear in the spleen. These T-RFC are much less stable than Thy 1- RFC (non-thymic-derived [B-RFC]) although most if not all of both classes of RFC adhere to nylon. T-RFC are induced with low doses of antigen (which fail to induce B-RFC) and are inhibited by higher antigen doses which are optimal for induction of B-RFC. Pretreatment of mice with cyclophosphamide prevents the high dose inhibition of T-RFC. Although there are many parallels between the production of T-RFC and delayed-type hypersensitivity (DTH) it is unlikely that the T-RFC are essential for DTH reactions since DTH can be transferred with cells which pass through nylon, and such cells are almost totally depleted of T-RFC. Thus immunization can lead to the production of large numbers of antigen-specific T-RFC whose functional role in the immune response is unknown. However, the characteristics of the T-RFC suggest that they may play an important role in amplification of suppressor cell activity.

CBA/N mice have an X-linked B-cell maturation defect which is reflected in part in an absence or dysfunction of a subclass of mature B cells. We have immunized the defective male offspring of the mating (CBA/N female X BALB/c male) with BALB/c spleen cells. The resulting antiserum (alphaLyb3) selectively reacts with a component on the surface of a portion of B cells from a panel of H-2 different mouse strains. Binding of alphaLyb3 serum to this B-cell subclass results in substantial (10- to 20-fold) enhancement of the antibody response to low doses of SRBC. Both binding and enhancing activity are removed by absorption with B cells from B6 and BALB/c, but not CBA/N mice. Absorption of the serum with bone marrow cells, T cells, or thymocytes from Lyb3+ strains does not remove activity. Since the enhanced plaque-forming cell (PFC) responses are specific for the immunizing antigen, and since no PFC response is produced by injection of the antiserum alone, this enhancement probably reflects a second signal produced by specific interaction between antibody and the surface Lyb3 component. Moreover, this signal can partially replace the requirement for T cells in the production of antibody to a "thymus-dependent" antigen. These findings (taken in conjunction with the previously described immune defects in CBA/N mice and other studies of B-cell maturation) suggest to us that Lyb3 is a cell surface component expressed selectively on a mature B-cell subclass. This component is important in B-cell triggering by antigen and fails to develop in CBA/N mice, due to a dysfunction of a regulatory gene on the CBA/N X chromosome.

Immunized Ly-1 T cells secrete an antigen-specific molecule that will induce Ly-2+ T cells to express suppressive activity. In two separate systems, factors that suppress the primary anti-sheep erythrocyte (SE) plaque-forming cell response of spleen cells in vitro (Ly-1 TsiF) or the contact sensitivity of azobenzenearsonate (ABA)-TsF1 consist of two macromolecules, one which binds antigen and is IJ-, the other which is I-J+ and does not bind antigen. Both of these chains are required for the factor's biological activity. These factors show a genetic restriction in their ability to induce suppression that is linked to the variable region of the Ig heavy chain gene complex (Igh-V). The I-J+ chain from the ABA-specific TsF1 could replace the I-J+ chain needed by the SE-specific Ly-1 TsiF for biological activity. Mixtures of ABA-binding chain with I-J+ material obtained from the SE-specific Ly-1 TsiF had no effect on the primary anti-SE response in vitro. In mixtures of SE antigen-binding chain from Ly-1 TsiF and I-J+ material from the ABA-specific TsF1, it is the I-J+ molecule that determined the factor's Igh-V restriction. Thus, the antigen-combining site of the factor determined the antigen specificity of this factor but is irrelevant to its Igh-V-linked genetic restrictions. The implications of these results for the idiotype network hypothesis are discussed.

The passive transfer of contact sensitivity (CS) by immune cells can be inhibited with an antigen-specific T suppressor factor. This factor is composed of two subfactors: an antigen-specific subfactor made by an Ly1+ cell (PC1-F) and a antigen nonspecific subfactor made by an Ly2+ T cell (TNBSA-F). The suppressive activity of the complete factor can be eliminated by depleting the assay population of Ly2+ cells, even though it is the Ly1+ cell in the population that transfers the adoptive immunity. This suggests that the Ly2+ cell in the assay population is needed to transduce the suppressive signal to the Ly1+ effector cell of DTH. We found that an Ly2+ cell from immune animals could be induced to produce a cell free subfactor that overcame the requirement for this Ttrans cell in the suppression of CS by TsF. The induction required only PC1-F, TNP-coupled spleen cells, and resulted in the production of an antigen-nonspecific I-J+ subfactor by immune Ly2+, I-J+ cells. The need for the Ly2+ transducer cell could also be overcome by addition of an I-J+ molecule secreted by Ly1 T cells hyperimmunized to SRBC. A suppressor complex made from mixing the I-J+ molecule with TNBSA-F could directly suppress the functional activity of immune T cells not only to transfer CS, but also to deliver help to B cells in an in vitro PFC response. This suppressive complex is antigen-nonspecific and does not require Ly2+ T cells in the assay population for suppressive activity. These results indicate that effector factors of the suppressor circuit require two molecules; one that contains the functional suppressor material and one that serves as a "schlepper," a molecule needed to deliver the suppression to the appropriate target cell. The ability to construct a functional suppressor complex from two subfactors raised against different antigens, using different immunization procedures, which were isolated from factors exhibiting different functional activities suggests that certain cells of the immune system may play a universal role in "transducing" the suppressive signal.

We have examined the ability of macrophages (Mphi) to transmit T-cell derived suppressor signals to other T cells. The suppressor signal studied is an antigen-specific factor which suppresses the ability of adoptively transferred, sensitized lymphocytes to express contact hypersensitivity in normal recipients. We have found that this factor binds to peritoneal exudate Mphi via cell surface structures which can be blocked with heat-aggregated gamma globulin. Dead (HK) Mphi bind the factor but fail to present it in a functional way to assay (immune) T cells, whereas live (L) Mphi perform both functions. Further, L Mphi can retrieve the factor in an active form from the surfaces of HK Mphi. Based on these and other findings (1-5), we discuss the possibility that Mphi may play as important a role in presenting T-cell communication signals to the cells of the immune system as they do in presenting antigen.

A series of Thy-1.2+ Ly-1+ Qa-1+ malignant T cell clones have been isolated from murine sarcoma virus-murine leukemia-Moloney (MSV-MuLV-M)-induced B cell lymphomas or from MSV-MuLV-M-infected B6 mice. These T cell clones enhance both antigen-independent and -dependent lymphocyte differentiation and function. They also induce the differentiation of granulocytes and erythrocytes in the stem cell compartment, a function that parallels the immunopathology of the disease in vivo. The malignant T cell appears to sustain B lymphoma growth in vivo by releasing a factor (BCGF) that promotes B cell proliferation.

We have tested the ability of several types of trinitrophenyl (TNP)-labeled Ia+ cells to induce contact hypersensitivity (CS) after intravenous injection. Most labeled cell types (spleen cells, splenic macrophages, various types of peritoneal-exudate cells) not only fail to induce CS after this type of inoculation but, rather, activate T suppressor cells leading to specific immunological tolerance. Occasionally, some of these immunizing cells managed to bypass the T suppressor system and induced CS. In those cases the response was short-lived and could be blocked by concomitant injection of trinitrobenzelsulphonic acid (TNBS), a potent inducer of T suppressor cells. In sharp contrast to these results, TNP-labeled splenic dendritic cells and TNP-labeled peritoneal-exudate cells induced by complete Freund's adjuvant had the following distinctive features: (a) They were always able to sensitize when injected intravenously, and the degree of sensitization they produced was roughly equivalent to that achieved by cutaneous application of picryl chloride, the chemically reactive form of TNP. (b) The response they elicited was long lived (i.e., lasted for greater than 3 wk). (c) Their sensitizing capacity could not be blocked by the concomitant injection of TNBS. (d) They elicited a response that could be adoptively transferred to untreated, normal recipients. These results indicate that the type of cell that first presents antigen to the immune system plays an important, even essential, role in determining the strength and duration of the subsequent immune response. In particular, the results suggest that some special antigen-presenting cells can induce a response that is relatively resistant to host suppressor mechanisms. Evidence that they do so by activating contrasuppressor cells is discussed.

The data presented in this paper show that the population of cells that adoptively transfer contact hypersensitivity are Lyt-1+ 2-, I-J- and nonadherent to V. villosa lectin. However, the adoptive transfer of immunity by this population of cells is successful only when the recipient has been treated in such a way as to impair the host immunosuppression mechanism. This population cannot, on its own, transfer immunity to adult, untreated naive recipients unless an additional population of immunoregulatory cells is present. This immunoregulatory population does not itself adoptively transfer immunity. This latter population is differentiated from the immune cells in that they are Lyt-1+ 2-, I-J+ and are adherent to V. villosa lectin. Both populations are required to adoptively transfer immunity to adult untreated naive recipients.

We have examined the possibility that hyperthermia, such as that occurring during fever, may benefit the immune response. The effect of temperature on the in vitro immune response of unprimed murine spleen cells against the antigen sheep erythrocytes was tested. Hyperthermia potently augmented the plaque-forming cell response. Temperature-sensitive events occurred early in the culture period. Subsets of lymphocytes were independently assessed for effects of temperature on their activation and function. We showed that the beneficial effect of elevated temperature on the plaque-forming cell response probably occurs during the priming stage of T helper cells, and neither improves the delivery of help or the activation of B cells, nor impairs suppressor T cell generation or function. We propose that this powerful immunopotentiating effect of hyperthermia may account for the selective value of the fever response. This suggests taht the monokine interleukin 1, which is the endogenous mediator of fever, may promote immune responses both through a direct action on lymphocytes, and indirectly by an action on the central nervous system resulting in fever.

The differentiation of cytotoxic T lymphocyte precursor cells (CTL-P) into CTL effector cells is a two-step process. In the first step, naïve CTL-P (CTL-PN) become activated (CTL-PA) but do not yet have the capacity to kill target cells. CTL-PA can be distinguished from CTL-PN because the former are far less sensitive than the latter to the effects of in vitro-generated suppressor cells. Thus, the addition of suppressor T cells (Ts) to a fresh MLC can totally inhibit the production of CTL from CTL-PN, whereas the same Ts only minimally affect the generation of CTL from CTL-PA. It is not known whether these Ts act directly on CTL-PN or on a helper cell needed for activation to CTL-PA. The production of CTL-PA can take place in allogeneic mixed leukocyte cultures (MLC) treated with the drug pyrilamine, or when heat-inactivated stimulator cells are used. Each of these treatments inhibits the differentiation of CTL-PA to CTL. However, if pyrilamine is removed, a nonspecific MLC-derived signal can induce these CTL-PA to become CTL, even in the presence of significant numbers of Ts. This two step process of differentiation of CTL-P to CTL may be analogous to the way naïve B cells become antibody-producing cells.

Immunized Ly-1+2-T cells (Ly-1 cells) make an antigen-specific soluble suppressor product (Lyl-1 TsiF) that will induce Ly-2+ cells to express suppressive activity but only if the Ly-2+ and the Ly-1 producer cell share genetic polymorphisms that are linked to the Igh locus and in particular that part where the Igh-V (or VH) is encoded. Ly-1 TsiF can be separated into entities, one binds antigen and does not express I-J determinants, and the other is I-J+ and does not bind antigen. Neither of these "subfactors" has biological activity, but a 50:50 mixture of them reconstitutes biological activity that expresses the antigen specificity of the antigen-binding molecule. Any of the three heterologous erythrocytes (antigens) studied can be used for immunization to produce the I-J+ nonantigen-binding factor, i.e., the I-J+ moiety makes no contribution to the factor's specificity. It does, however, determine the intact factor's Igh-V linked restriction. Thus, the antigen combining site of the factor is irrelevant to the factor's Igh-V restriction but crucial for its specificity. The I-J+ molecule does not bind antigen nor influence the factor's antigen specificity but expresses the Igh-V polymorphism (or anti-Igh-V polymorphism) that is required for the transmission of an inductive signal to the factor's Ly-2+ acceptor cell.

The in vitro antibody response of spleen cells from B10 strain mice is not suppressed by factor preparations made by primed Ly-2 T cells, although these preparations can suppress the in vitro antibody response of spleen cells from other mouse strains (1-3)2. The factor preparations from Ly-2 cells contain at least two separable activities: one that acts as a suppressor moiety (Ly-2 T cell suppressor factor [Ly-2 TsF]) and a second factor that acts as an inducer of contrasuppression (Ly-2 TcsiF); the latter initiates a series of cellular interactions that leads to the inhibition of suppression that we refer to as contrasuppression. Removal of components (either cellular or humoral) of the contrasuppressor circuit makes spleen cells from B10 strain mice as easily suppressible as are those of other mouse strains. Thus, removal of the contrasuppressor inducer cell and/or its biologically active product with the use of an anit-J serum, or removal of the functional acceptor of the inducer cell with the same or other (Ly-2; Qa-1) antisera breaks the B10 suppressor barrier. Contrasuppressive activity. but not helper activity can be eluted from anit-I-J immunoabsorbents. The addition of B10 T cells to either B6 or B10 spleen cell culture deprived of acceptor cells for the TcsiF reconstitutes contrasuppression more efficiently than does the addition of C57BL/6 T cells. Ly-2 TcsiF is more cross-reactive than is Ly-2 TsF so that absorption of factor preparations from sheep erythrocyte-primed Ly-2 cells with horse erythrocytes also breaks the B10 suppressor barrier. The hyperresponsiveness of splenic T cells from B10 strains to Ly-2 TcsiF may be an in vitro exaggeration of a normal in vivo process. Thus it is possible that one can take advantage of this unusual situation to help dissect out the cellular and subcellular components of T cell circuits that moldulate sensitivity to immunoregulatory signals.

We have described an interaction between two T cells subsets that results in interference with the expression of Ly-1-, 2+ (Ly-2) T cell-mediated suppression. We refer to this novel immunoregulatory activity as contrasuppression. The T cell responsible for the induction of contrasuppression (inducer cell) expresses the phenotype Ly-1-, 2+;I-J+;Qa-1+. This phenotype distinguishes it from the suppressor effector cells which we find to be I-J-2.3. An I-J+ soluble mediator from the contrasuppressor inducer cell acts on another cell (acceptor cell) that expresses the phenotype Ly-1+, 2+; I-J+; Qa-1+. This phenotype distinguishes it from T helper cells. Both the inducer cell (or its biologically active mediator) and its acceptor cell are required for the expression of contrasuppression. Because contrasuppressor cells can block the suppressive activity of cell-free mediators released by Ly-2 suppressor T cells, the mechanism of contrasuppression is either separated from or in addition to the inactivation of suppressor cells themselves. The potential importance of contrasuppressor activity in the regulation of suppressor T cell activity in allowing immunologic memory to be expressed and in permitting microenvironmental immune regulation is discussed.

Antigen-stimulated Ly1:Qa1+ cells induce a nonimmune set of T-acceptor cells (surface phenotype Ly123+Qa1+) to participate in the generation of specific suppressive activity. The experiments reported here were designed to test the possibility that the interaction between T-inducer and T-acceptor cells might be governed by genes linked to the Ig locus. We find that inducer:acceptor interactions occur only if the inducer and acceptor T-cell sets are obtained from donor that are identical at the Ig locus and are independent of the Ig locus expressed on the B cells used for assay of T-helper activity. In addition, experiments using inducer and acceptor T cells from the congenic recombinant BAB. 14 strain show that T-T interactions are not governed by Ig-CH genes, per se. These data indicate that T-inducer: T-acceptor interactions are governed by Ig-linked genes that may control expression of VH-like structures on T cells, or control expression of as yet unidentified cell-surface molecules.

Antigen-specific factors associated with immunosuppressive activity, released by cultured T cells from mice tolerant to the haptens trinitrophenyl, dinitrophenyl and oxazolone, were purified by hapten affinity chromatography. Their binding specificity for antigens paralleled their immunoregulatory activity. Like some immunoglobulin molecules, these factors had blocked NH2 termini and could be bound to Fc-like receptors on macrophages. However, neither immunoglobulin constant region determinants (isotypes) nor antigens encoded by the major histocompatibility complex were detected on the suppressive factors. The purified factors occurred as 68,000-dalton proteins and non-covalently linked dimers. No associated immunoglobulin light chain molecules were detected. The factors showed a marked propensity toward degradation with major breakdown products of 45,000-50,000 and 25,000-30,000 daltons. These results suggest that these molecules are the T-cell products analogous to B-cell immunoglobulin (equivalent to heavy chains) and that they may be the antigen-specific components which act in conjunction with major histocompatibility-controlled gene products to perform antigen-specific suppression.

T cells that have been immunized to express optimal levels of contact hypersensitivity upon adoptive transfer to normal animals can be inhibited from doing so by incubating them with an antigen-specific T suppressor factor. This factor is composed of at least two subunits which come from cells expressing different Ly phenotypes; an antigen-specific antigen-binding "subfactor" is made by an Ly-1 cell and a non-antigen-binding one is made by an Ly-2 cell. Neither of these cells nor their products express detectable amounts of major histocompatibility gene products. The mode of immunization plays an important role in determining which of these subfactors will be produced. Painting the skin with a reactive hapten immunizes Ly-1 cells that secrete antigen-binding material, whereas intravenous injection of trinitrobenzenesulfonic acid activates Ly-2 cells to produce a second subunit that does not see antigen. There is reason to believe that the molecule that does not bind to antigen does have some antigen specificity. An analysis of the data at hand suggests that the antigen specificity stems from an interaction of the two subunits described with yet another subunit and that biological activity is dependent upon three macromolecules. Thus, the complex level of cellular interactions that regulate immunity may also be reflected in a similar type of complexity in the interaction between their biologically active cell-free products.

Purified Ly1 cells induce other T-cell sets to exert potent feedback inhibitory activity and this T-T interaction has been shown to play an important role in regulating in vivo immune responses. Approximately 2/3 of Ly1 cells also express the Qa1 surface phenotype (Ly1:Qa1+ cells). The experiments reported here indicate that Ly1:Qal+ cells are responsible for induction of feedback inhibition and that signals from both Ly1:Qal+ cells and Ly1:Qal- cells are required for optimal formation of antibody by B cells.

Normal T and immune B lymphocytes interact in a fashion that leads to suppression of the immune response. Normal spleen cells added to cultures of primed spleen cells specifically suppressed both the IgM and IgG secondary antibody response of the primed cells to less than 30% of the response of the immune cells cultured alone. Cell crowding as a possible in vitro artifact was ruled out. The suppression was specific for the priming antigen, even when the specific and nonspecific antigens were included in the same cultures. Suppression required both normal T and immune B cells to be present in culture. We suggest that the immune population produces a signal that can induce normal T cells to become specific suppressor cells. This form of interaction may represent an important regulatory (homeostatic) mechanism in the immune system.

Cell-mediated immunity includes both the generation of cytotoxic cells and initiation of delayed-type hypersensitivity (DTH). The resting T-cell population, before stimulation by antigen, already contains cells of the Lyl subclass that are programmed to initiate DTH (and helper function) but not cytotoxic responses, as well as Ly23 cells which can generate killer activity (and suppressive function) but not DTH. The central implication of these findings is that the broad division between humoral and cell-mediated immune responses does not precisely correspond to the division of labor among T-cell subclasses. The relative contribution of DTH-competent Lyl cells and cytotoxic Ly23 cells to the classical homograft response remains to be determined.

The intensity of Lyl+T helper and delayed type hypersensitivity effector cell activities is governed, in part, by an interplay between two classes of immunoregulatory T cells: suppressor cells and contrasuppressor cells. We asked whether histamine, at concentrations and duration of exposure that we calculated might be achieved at local sites of inflammation, could activate either or both of these classes of regulatory cells in vitro. To answer this question we used spleen cells from mice treated in vivo with the toleragen trinitrobenzenesulfonic acid as regulators of in vitro generation of primary anti-trinitrophenyl self-cytotoxic T lymphocytes. Under the conditions used, these spleen cells had no major regulatory effects. However, if these cells were preincubated with histamine at 0.1 mM for 30-60 min, suppressor activity was induced, but this occurred inconsistently and with nonstoichiometric results. The use of synthetic histamine agonists revealed that histamine may activate both suppressor and contrasuppressor cell subsets. A histamine H1 receptor agonist [2-(2-pyridyl)-ethylamine dihydrochloride] had a propensity to activate contrasuppression, whereas an H2 receptor agonist (dimaprit) tended to activate suppressor cells. Thus, histamine may have opposing actions that obscure suppression. This duality was shown by treatment of pyridylethylamine-induced contrasuppressor cells with complement and anti-I-J antibody that kills contrasuppressor cells. This treatment revealed a high level of suppressor cell activity that was not expressed until the opposing contrasuppressor cells were removed. Because histamine is released at local sites of delayed type hypersensitivity, these results indicate that histamine may serve as an inducer of microenvironmental immunomodulation by activating regulatory T cells at sites where immune responses are taking place.

Antigen-primed T cells have been shown to require I-region-compatible adherent cells, as well as the priming antigen, to proliferate in vitro. We postulated that the Ia-recognition event is required for the T cell to induce secretion of the monokine interleukin 1 (IL 1) from adherent cells; the conventionally held view is that Ia is directly required for T cell activation. Our hypothesis predicts that IL I could replace the requirement for Ia+ cells in T cell proliferation assays in vitro. To test this prediction, we depleted keyhole limpet hemocyanin (KLH)-primed C57BL/6 mouse lymph node cells of I-A+ cells by treating with monoclonal anti-I-Ab and complement. As expected, this treatment eliminated the ability of KLH to provoke a proliferative response by primed T cells. Proliferation was restored by providing exogenous IL 1, but only in conjunction with added KLH. The proliferative response of primed T cells could also be blocked by adding anti-I-Ab to culture, and this inhibition could similarly be reversed by providing IL 1 in the presence of the specific antigen KLH. On the basis of these findings we propose a model of T cell activation and discuss its implications.

In the course of a survey of healthy Korean military personnel in an area where viral hepatitis is endemic, about 30 cases of anicteric hepatitis were detected. Their clinical and laboratory manifestations were described in the preceding paper.1 It is the purpose of this report to describe the histologic changes based on three liver biopsies of each of the patients during a three-month period of observation, to describe the histologic evolution during the period of study, and finally to speculate on the relation between anicteric hepatitis and cirrhosis. MATERIALS AND METHODS Thirty-two cases detected among clinically healthy military personnel by serum transaminase tests, as described in the preceding paper,1 were submitted to serial liver biopsy during a period of up to three months' ambulatory hospitalization.First biopsies were performed with a Menghini needle by the intercostal approach 2 two to eight days after the initial SGPT test. A

The incidence and clinical and laboratory features, as well as the structural alterations, of anicteric hepatitis are not established. Evidence for its existence is based on sporadic cases occurring simultaneously with icteric viral hepatitis in circumscribed outbreaks.As a result of a mass serum enzyme survey originally designed to detect pre-icteric cases of viral hepatitis in an endemic population, 32 cases were uncovered on the basis of significantly abnormal serum activities of glutamic pyruvic transaminase (SGPT). These cases were hospitalized for intensive clinical, laboratory, and histopathologic study. The present report summarizes the clinical and laboratory findings in this series of patients. Their pathologic findings, described in the following paper,1 serve in addition to indicate that this group of patients represented a disease entity of chronic, active hepatitis. MATERIALS AND METHODS SGPT activity was determined in 1,906 soldiers of the Republic of Korea Army, who had recently passed a physical