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A significant innovation for future indoor wireless networks is the use of the mmWave frequency band. However, an important challenge comes from the restricted propagation conditions in this band, which necessitates the use of beamforming and associated beam management procedures, including, for instance, beam tracking or beam prediction. A possible solution to the beam management problem is to use artificial-intelligence-based procedures to learn the hidden spatial propagation patterns of the channel and to use this knowledge to predict the best beam directions. In this paper, we present a deep-neural-network-based method that has memory that can be used to predict the best reception directions for moving users. The best direction is the highest expected signal level at the next moment. The resulting method allows for a user-side antenna management system. The result was evaluated using three different metrics, thus detailing not only its predictive ability, but also its usability.

We studied inactivation of HIV-1 by fresh sera of animals. We found that while fresh sera of humans and chimpanzees (among others) did not have antiviral activity, fresh sera of several other mammals, especially those of rodents and felines, showed a dose-dependent viral-inactivating property against cell-free HIV-1; these sera were also capable of inactivating virus preadsorbed to cells, similar to neutralizing antibody. The activity was destroyed by heating to 56 degrees C, required Ca2+ but no antiviral antibody, and therefore apparently involves the classical complement pathway. The activity could not be ascribed to any single fraction of sera separated on a size exclusion HPLC column. Mouse serum (the only one tested) also inactivated HIV-2. The data are consistent with classical C-mediated pathway inactivation of HIV-1 and HIV-2 by animal sera and is the first report of any "complement-like" antilentiviral serum factor. Elucidation of this mechanism may aid in understanding the lack of activity of human serum against HIV-1 and may prove useful in combined interventive strategies against HIV-1.

Lysis of autologous sheep red cells (labeled with methotrexate as the target hapten) by neat autologous serum was studied. The results indicated that the efficiency of lysis under physiological concentrations of cells and serum was about the same as lysis of the same target cells sensitized with autologous antibody and guinea pig serum as the source of complement. The data also indicate that the one-hit mechanism of immune lysis operates under near physiological conditions.

Line-1 guinea pig hepatoma cells are susceptible to killing by anti-Forssman IgM antibody plus guinea pig complement (GPC). When these tumor cells are incubated with insulin, epinephrine, hydrocortisone, or prednisolone, the cells show a marked reduction in their susceptibility to antibody-C-killing. If the ability of the cells to synthesize DNA, RNA, and protein is impaired by pretreatment with metabolic inhibitors, x-irradiation, or culture in nutrient-deficient media, the hormones are no longer effective in rendering the cells resistant to killing. If only DNA synthesis is impaired, but not RNA and protein synthesis, the hormones are effective. The inability of cells inhibited in their macromolecular synthesis to be rendered resistant to killing after hormone treatment is not due to an inability of the cells to bind hormone.

We have investigated the binding and activation of C1 by IgG-anti methotrexate antibody at cell surfaces. Under conditions where variation in cell surface hapten density had no effect on binding of IgG, the number of C1 (or its active form, C1) bound by the IgG was independent of hapten density. The ability of the C1 binding IgG complex to activate C1, however, was decreased with decreasing density of the hapten. The decreased ability to activate bound C1 was paralleled by decreased ability to activate the hemolytic sequence in whole complement. The results were interpreted to mean that binding of C1 was the result of aggregation (doublet formation) by IgG while activation of the bound C1 depended on changes induced in the IgG molecule by straddling hapten molecules at varying distances.

Serotherapy and plasma therapy have proved to be effective in the treatment of diverse neoplasms. The mechanisms of the tumoricidal or growth-inhibitory effects are unknown. We previously reported that activation of the alternative pathway of complement in absorbed sera correlated with the presence of anti-tumor activity. Complement components generated during absorption may serve as the initial mediators of cytotoxicity; for example, C5a may function in its role as a chemo-attractant. To further investigate the anti-tumor mechanisms, we undertook a series of sequential histological studies of in vivo changes in tumors following i.v. serotherapy. We found diffuse inflammatory cellular infiltrates in the interstitial compartments of primary mammary carcinomas of rats within 3-4 hr of administration of protein A-Sepharose absorbed syngeneic serum. The number of inflammatory cells was significantly higher in tumors from treated rats: total infiltrating cells (p = 0.002), eosinophils (p = 0.001), neutrophils (p = 0.001), macrophages (p = 0.001), lymphocytes (p = 0.004) and plasma cells (p = 0.001). Also, the mitotic index of tumor cells was significantly lower 4 hr after serotherapy when compared with that of untreated rat tumor cells. C3 in tumor tissue was decreased at 4 hr following serotherapy. Fibrosis was present in tumor nodules with retarded growth 5 weeks after the start of serotherapy. Localization of the infiltrating cells to tumor interstitial compartments prevents direct contact between inflammatory cells and neoplastic cells, making it unlikely that direct cell-cell killing occurs. Indirect cell killing within the tumor bed apparently occurs through several mechanisms involving interactions between serotherapy-initiated humoral mediators and inflammatory cells. The resulting anti-tumor effects include microvascular injury leading to localized ischemia, tumor infarction, and fibroblastic reactions obstructing tumor invasion and growth.

The hemolytic efficiency of rabbit-anti-Forssman IgM antibody depends on the source of complement components. With whole guinea pig complement as few as one in 10 IgM molecules was hemolytic; it was found that with purified guinea pig C1, C4, and C2 components and with rat late-acting components, all IgM molecules were hemolytic. Evidence indicates that the block occurred as a result of generating at least two different cell-bound C4 molecules, one of which was not competent with homologous late-acting components.

The inhibitory effect of metal salts on the formation and transformation of E to ghosts was studied. Ferrous and ferric salts inhibited the binding of C9 to EAC1-8 cells but had no other inhibitory role in the reaction. Uranly, copper, and zinc salts inhibited the transformation of the EAC1-9inserted intermediate to E ghosts. This inhibition occurred at a stage prior to detectable damage as measured by 86Rb or hemoglobin release and at a step prior to that inhibitable by high molarity EDTA. Consequently a further step in the reaction sequence of E to ghosts was identified. The reaction sequence leading from EAC1-9 to ghosts can be summarized as follows: formula: (see text).

After treatment with aminoethylisothiouronium bromide hydrobromide (AET), the ascites forms of the diethylnitrosamine-induced guinea pig hepatomas, line-1 and line-10, were susceptible or more susceptible to killing in vitro by certain combinations of tumor-specific or IgM anti-Forssman antibody and either human or guinea pig complement. Since AET could be toxic to either cell line, conditions of pH, concentration of AET, and duration of exposure of the cells to the reagent were determined that resulted in enhanced susceptibility without significantly affecting cell viability. Chicken erythrocytes (CE) also were tested and AET-treated cells found to be more susceptible to lysis by IgM anti-Forssman antibody and guinea pig complement. The enhancement apparently was not due to increased ability of AET-treated CE to fix antibody. In contrast to CE, the lytic susceptibility of sheep cells was not affected by AET treatment. In addition to AET, several drugs and enzymes that also can affect the susceptibility of the tumor cells to antibody and complement were tested and found to be ineffective against CE. Since AET reputedly acts directly on the cell surface, it seems reasonable to assume that the increased susceptibility of the tumor cells and CE to antibody and complement may result from a modification of the cell surface.

We reported inhibition of growth of primary rat mammary carcinomas after infusions of tumor-bearer plasma absorbed with Protein A-Sepharose or inactivated CNBr Sepharose. Absorbed plasmas were depleted of the third component of complement (C3) (other complement components defined similarly) and C5 but not C1, C4, or C2. These results suggested that activation of the alternative pathway of complement might be involved in the observed antitumor effects. To test this concept sera were treated with ethylenedinitrilotetraacetic acid or [ethylenebis(oxyethylenenitrilo)]tetraacetic acid before absorption with Protein A-Sepharose. Ethylenedinitrilotetraacetic acid, by chelating calcium and magnesium, prevents activation of both the alternative and classical complement pathways. [Ethylenebis(oxyethylenenitrilo)]tetraacetic acid, by chelating calcium but not magnesium, permits activation of the alternative pathway but inhibits activation of the classical complement pathway. Sera in the presence or absence of chelating agent were absorbed with Protein A-Sepharose twice at room temperature. After absorption calcium was added to the sera. Rats were treated by i.v. injection of sera twice a week for 2 weeks. Measurements of tumor size were made weekly for 5-7 weeks and then tumor weight was determined. Groups were compared both for size of index and total tumors. The results can be summarized as follows: tumor-bearer sera before absorption did not inhibit the growth of rat primary mammary carcinomas; tumor-bearer sera after absorption with Protein A-Sepharose showed significant consumption of C3 and did inhibit tumor growth; tumor-bearer sera absorbed in the presence of ethylenedinitrilotetraacetic acid did not show a decrease in C3 functional activity and did not inhibit tumor growth; tumor-bearer sera absorbed in the presence of [ethylenebis(oxyethylenenitrilo)]tetraacetic acid did show a decrease in C3 functional activity and did inhibit tumor growth; sera from normal adult female rats after absorption with Protein A-Sepharose did inhibit tumor growth. The results are consistent with a role for the alternative pathway of complement in the inhibition of growth of rat primary mammary carcinomas observed after treatment with absorbed sera.

The mechanism of the terminal steps in the lysis of antibody-sensitized tumor cells by complement (TAC) was studied. It was shown that once complement has reacted, lysis proceeded even in the absence of fluid-phase complement. Transformation of TAC to dead cells was found to be at least a two-step process: one of the steps was temperature dependent whereas the other was reversibly inhibited by EDTA. In analogy to the hemolytic system, TAC has been designated T.

Oral tumors with associated cervical lymph node metastases developed after injection of tumor cells into buccal pads of inbred guinea pigs. Intralesional injection of living BCG or BCG cell walls (CW) caused regression of established tumors, prevented the development of cervical lymph node metastases and led to the development of host resistance to the growth of subsequent tumor transplant.

Methods for preparing chicken erythrocytes (CE) with C7 bound to their surface were devised by using either the classical pathway (CEA1-7) or an activated 56hu reagent (CE567) derived from inulin-treated human serum. These intermediates were used to study the lysis of CE by functionally purified C8 and C9 isolated from guinea pig and human serum. The results indicated that GPC9 was less efficient in lysing CEA1-8 or CE5678 than HuC9. This finding was observed irrespective of the species of C8 used. Experiments designed to analyze this difference indicated that there were two functionally distinct forms of C5b-8 that were randomly distributed among the cells but differed in their ability to generate a C lesion depending on the species of C9 used to complete the reaction. The implications of these results on the mechanism of generation of C lesions are briefly discussed.

We studied the effect of an IgG anti-IgM on the dissociation of cell bound IgM anti-hapten antibody, as measured with fluid phase hapten. Methotrexate (MTX) covalently bound to the red cells surface was used as hapten; rabbit anti-MTX IgM and rabbit anti-allotype IgG reactive with the IgM were used as antibodies. The amount of cell bound antibodies was measured with 125I-labelled protein A. In the absence of the anti-allotype antibody, most of the anti-hapten IgM was prevented from reassociation by fluid phase hapten. In the presence of the anti-allotype IgG most of the anti-hapten IgM was non-dissociable, with about a 1000-fold increase in the apparent binding constant. We found that (1) dissociability of the anti-hapten IgM depended on the density of the cell bound hapten, (2) decrease in dissociability was a function of the anti-allotype antibody concn and (3) even in the presence of excess anti-allotype antibody dissociability was an inverse function of anti-hapten IgM concn.

A number of metabolic inhibitors and chemotherapeutic agents have been found to increase the sensitivity of a chemically induced guinea pig hepatoma (line 1) to killing by antibody and complement. We have investigated whether the mechanism whereby these drugs increase sensitivity to killing is attributable to their primary action of inhibiting DNA, RNA, or protein synthesis. Line 1 cells incubated for 1, 4, or 17 hr with actinomycin D (25 microng/ml), adriamycin (40 microng/ml), or puromycin (5 micron/ml) or with 5-fold lower concentrations of these drugs were maximally inhibited (greater than 90%) in their ability to synthesize DNA, RNA, and protein within 1 hr. However, only cells incubated for 17 hr with the high concentrations of drugs showed increased sensitivity to killing by antibody and complement. Line 1 cells incubated with high concentrations of these drugs of 17 hr, washed, and resuspended in drug-free medium recovered their resistance to killing by antibody and complement within 4 hr. These cells ever after culture for 24 hr in drug-free medium did not regain their ability to synthesize DNA, RNA, or protein. A similar lack of correlation between synthesis of these macromolecules and sensitivity to antibody-complement-mediated killing was observed after the cells were treated with physical agents that inhibit macromolecular synthesis. Both heat-treated and X-irradiated cells were inhibited in their ability to synthesize DNA, RNA, and protein immediately after treatment; however, only X-irradiated cells (6 and 16 hr postirradiation) were increased in their sensitivity to antibody-complement-mediated killing. Our data show that the ability of line 1 tumor cells to resist humoral immune attack does not depend solely on their ability to synthesize DNA, RNA, or protein.

The ability of IgG antibodies with different hapten specificities to fix C1 and activate C as a function of hapten density on a red cell surface was investigated. Rabbit anti-methotrexate and anti-folinic acid IgG antibodies in a mixture were highly efficient in fixing C1 and activating C when cells carried simultaneously high levels of both haptens. We wished to find out whether in a C-activating IgG complex both IgG molecules had to be in a form that could activate C1. By reducing hapten density of one of the haptens on a double labeled cell, complexes were generated where only one in a pair of IgG molecules was in the activating form; such a pair had the same activating efficiency as a pair in which both IgG molecules were in the activating form. It was concluded that cooperative activation of C in C1-binding IgG complexes required only one IgG in the complex to be in the activating form.

Sheep erythrocytes pretreated with supernatants of mouse spleen or thymus cells become resistant to lysis by guinea pig complement. The inhibitory activity (IA) reduces the utilization of C2 by EAC14. Because IA binds to the surface of sheep erythrocytes and does not inhibit C1 irreversibly, it is probably a hitherto undescribed inhibitor of complement.

Staphylococcal protein (A (PA) and IgG anti-Forssman immunoglobulin formed complexes that behaved functionally like IgM in their ability to lyse sheep erythrocytes (E) in the presence of whole guinea pig complement (GPC) and to fix purified guinea pig C1. Concanavalin A, a plant lectin that inhibited IgM but not IgG hemolytic activity, inhibited the hemolytic activity of IgG-protein A complexes that behaved like IgM but had no effect on complexes that behaved functionally like IgG. Since Con A is known to bind specifically to glucose and mannose residues, our results suggested that the interaction of protein A with the Fc region of IgG led to exposure of sugar moieties that may participate in complement (C) binding. The production of IgM-like complexes depended on the ratio of protein A to IgG and the empirical formula of these IgM-like complexes was found to be [(IgG)2PA]n. As the ratio of PA to IgG was increased, the resulting complexes tended to behave functionally like IgG but with reduced hemolytic activity and C1 fixing ability. Furthermore, the binding of C1 to EIgG was inhibited by PA and the binding of PA to EIgG was inhibited by C1 indicating that the binding sites for C1 and PA were located near each other or were identical. Our results offer a reasonable explanation for the reported effects of PA or mixtures of PA and IgG in vitro and in vivo.

The inhibitory effects of 0.1 M EDTA on the lysis of E prepared by incubating EA with whole GPC was studied. At high end point lysis (greater than 70%) 0.1 M EDTA failed to prevent hemoglobin release whereas at lower end point (less than 60%) 0.1 M EDTA was effective. In all cases hemoglobin release was inhibited by 25% BSA. When E were prepared by incubating EAC1-8 with C9, similar results were obtained. In this system the difference in the ability of 0.1 M EDTA to inhibit hemoglobin release at high or low end point lysis could not be correlated with the low end point lysis could not be correlated with the number of lesions/cell but appeared to be related to the C9 to SAC1-8 ratio. With limiting SAC1-8 and excess C9, E were produced from which hemoglobin release could not be prevented by 0.1 M EDTA whereas at lower C9 to SAC1-8 ratios hemoglobin release was prevented by 0.1 M EDTA. These differences most probably reflect functionally different sized transmembrane channels that were produced at different C9 to SAC1-8 ratios.

Concanavalin A (Con A) was found to inhibit the killing of antibody-sensitized line-1 tumor cells (TA) by guinea pig complement (GPC) but not by human complement (HuC). Other plant lectins (wheat germ, leucoagglutinin, and pokeweed mitogen) were also tested but Con A was the only lectin found to inhibit antibody-GPC-mediated killing. The inhibitory effect of Con A was observed when the GPC was mixed with Con A or when the antibody-sensitized cells were pretreated with Con A (TA-Con A) before the addition of GPC. The effect could be reversed by treatment of such cells with alpha-D-methylglucopyranoside or by incubation at 37 degrees C for approximately 2 hr. Con A appeared to act by preventing the binding of the first component of GPC (GPC1) to antibody-sensitized tumor cells. Differences in the binding of the first component of HuC (HuC1) and GPC1 to TA-Con A suggested that a difference in the binding site for HuC1 and GPC1 might exist. There was no difference in the number of GPC1 molecules fixed to antibody-sensitized sheep erythrocytes (EA) or EA treated with Con A in experiments using the same antibody as used with the tumor cells and the same Con A preparation. It would consequently appear that the inhibitory effect of Con A on the binding of GPC1 to TA is not due solely to an interaction of Con A with the antibody.

Dissociation of the C1q subcomponent in native C1 upon dilution was reexamined by using ultracentrifugation in a sucrose gradient and high performance liquid chromatography system with a size exclusion column for separating the dissociated C1q fractions. The antigenic content of C1q in each fraction was detected by ELISA and Western blotting; binding to erythrocyte antibody was also determined. The results confirmed a previous claim that C1q in native C1 dissociated as a function of dilution: up to 14.5% of C1q antigen was in the low molecular weight form (approximate S value: 4-5). Commercial preparations of purified C1q also contained C1q antigen in the low molecular weight form.

Rabbit anti-methotrexate (MTX) IgG antibody was used to study the effect of MTX density on sheep red cells on the lysis of cells by complement (C). Under conditions in which the density of IgG did not vary, the number of lytic IgG complexes remained approximately the same when the average distance between MTX molecules was between 5 and 7 nm, but decreased rapidly with an average distance less than 10 nm. The results were interpreted to mean that in addition to aggregation for IgG to acquire maximal C in fixing and activating properties, the angle of the Fab arms of the molecule must not be larger than about 50 to 60 degrees. The data also suggested IgG molecules with Fab angles of less than about 30 degrees might also not be able to induce C-mediated cell lysis.

The interaction of d.l. activity with chicken red cells (CE) generates a cell intermediate with the properties of classical E*. Generation of CE* by d.l. activity at 37 degrees C is rapid, while there is a considerable lag in the conversion of CE* to ghost and hemoglobin. Conversion of CE* to ghosts can be blocked by high concentration of EDTA and/or 0 degrees C. CE* contain at least C6 and C9 on their surface.

Agents that increase (certain metabolic inhibitors, chemotherapeutic agents, and x-irradiation), decrease (hormones), or have no effect (hyperthermia) on the susceptibility of line-1 and line-10 guinea pig hepatoma cells to humoral immune attack were studied for their effects on the ability of these tumor cells to synthesize macromolecules. A correlation was found between the drug-induced increase in sensitivity of these cells to antibody-C mediated killing and the loss of their ability to incorporate fatty acids into complex cellular lipids. Similarly, the hormone-induced increase in resistance of the cells to killing was accompanied by an enhancement in complex lipid synthesis by these cells was also observed after the cells were exposed to physical means of insult (x-irradiation or hyperthermia). No correlation was found between the sensitivity of the cells to antibody-C mediated killing and their ability to synthesize DNA, RNA, protein, or complex carbohydrate, or their capacity for de novo lipid synthesis as measured by incorporation of acetate and glycerol into cellular macromolecules. The assembly of free fatty acids into complex lipid moieties is therefore proposed to be of fundamental importance for the ability of the tumor cells to resist humoral immune killing.

Binding and activation of complement (C) by anti-hapten IgG and IgM antibodies (Abs) bound to a cell surface are dependent on the density and presumably on the distribution of cell-bound hapten. The purpose of this study was to find out if altering the distribution of the hapten on a red cell surface could modify the ability of anti-hapten IgG or IgM Ab to activate C. To test this we devised methods for comparing the C binding and activating efficiency of Abs bound to a hapten distributed randomly or in patches on cells. Random distribution was achieved by the covalent binding of methotrexate (MTX) directly to sheep red blood cells (E), while patchy distribution was achieved by the convalent binding to E of bovine serum albumin-MTX complexes. We considered bound albumin molecules as patches of MTX molecules. The results showed that, for IgG Ab, the number of hapten/E and the number of anti-hapten Ab molecules/cell required to generate one C-activating IgG complex were about an order of magnitude lower for hapten bound in patches than for randomly bound hapten. In contrast, IgM Ab bound to a hapten distributed in patches on an E surface lacked the ability to activate the lytic sequence of C, although maintaining a full ability to binding C1.

Spontaneous activation of C1r in the presence of EDTA was examined by a Western blot. Partially purified native C1r was prepared by ultracentrifugation of fresh serum in 10 to 30% sucrose gradient; final concentration of C1r was one-sixth of the original serum. C1(-)-INH was not detectable by a single radial immunodiffusion (less than 0.5% of serum). The results demonstrated that 1) the rate of spontaneous activation of C1r was slow (less than 10% in 30 min); 2) it was concentration-dependent; 3) it was enhanced by activated C1r; and 4) it was almost completely suppressed by serine protease inhibitors up to 1 h. These results were inconsistent with an intramolecular autoactivation model of C1r in the fluid phase and suggested intermolecular activation by contaminating protease or activated C1r.

The inoculation of a mixture of drugs and guinea pig hepatoma cells (line-10) induced tumor-specific immunity in about 20% of guinea pigs. When guinea pigs with established intradermal tumors were given various drugs ip, no cures were observed; in contrast, multiple intralesional injections of actinomycin D, 1,3-bis(2-chlorethyl)-1-nitrosourea, adriamycin, mitomycin C, and melphalan were effective in curing animals of their intradermal tumors at a time when there were tumor cells in the draining lymph nodes; dimethyl-triazenoimidazole carboxamide, methotrexate, 5-fluorouracil, and 6-mercaptopurine were not effective. More than 80% of the cured animals were immune to rechallenge with 10(6) line-10 tumor cells.

We have previously shown that 0.1 M EDTA could be used to distinguish functionally different transmembrane channels produced during complement-(C) mediated hemolysis of E. In this paper we have studied the ability of sugars of varying Stokes' radii to prevent hemoglobin release from E intermediates whose lysis was inhibitable or not inhibitable by EDTA. On the basis of these experiments we propose that the inhibition of E transformation by high molarity EDTA occurs by virtue of the size of the EDTA molecule in solution. Studies on the effect of EDTA on red cell lysis induced by polyene antibiotics that form transmembrane channels of a defined size support this conclusion. The results of these experiments were interpreted to mean: 1) The EDTA inhibitable lesion of E has a smaller effective radius than the noninhibitable lesion; 2) the effective radius of the smallest lesion that yields a lytic site was less than 3.6 A; 3) the lesions produced in the red cell membrane by C are not uniform but vary in size depending on the C9 to SACl-8 ratio used to produce E.

Two antigenically distinct diethylnitrosamine-induced guinea pig hepatoma cell lines, line-1 and line-10, sensitized with rabbit anti-Forssman or with tumor-specific antibody, were more susceptible to killing by human complement (HuC) than by guinea pig complement (GPC). This difference could not be ascribed to differences in the amount of C1, C4, and C3 fixed: millions of C4 and hundreds of thousands of C3 were detected on cells whether they were killed or not killed by the C sources. Tumor cells sensitized with anti-Forssman IgM antibody generally had more GP C4 and C3 than Hu C4 and C3 bound to their surfaces. Cells sensitized with anti-tumor antibody generally had more Hu C4 and C3 than GP C4 and C3 bound to their surfaces. The resistance to killing of nucleated cells by antibody and C may be due in part to intrinisic properties of the cell.

Line-1 diethylnitrosamine-induced guinea pig tumor cells can be rendered sensitive to killing by rabbit anti-Forssman IgM antibody plus guinea pig complement (GPC) or antitumor antibody plus GPC following prolonged incubation (17 hr ) of the cells with one of several metabolic inhibitors. Compared to control cells, these cells have been shown to be inhibited in their ability to incorporate fatty acids into complex cellular lipids, which suggested that lipid synthesis is of fundamental importance for the ability of the tumor cells to resist humoral immune killing. In this study, drug-treated cells that were rendered sensitive to killing by anti-Forssman antibody plus GPC, but not antitumor antibody plus GPC, were inhibited in their incorporation of saturated (palmitic or stearic acid), but not an unsaturated, fatty acid (linoleic acid). These data suggested that the fatty acid composition of specific lipids may also be important for the resistance of these tumor cells to killing by antibody and complement.

The activation of classical C pathway by immune complexes depends on the binding and activation of C1, the first component of C. The Ig in the complex must be of the right class and in the right configuration to accomplish the conversion of precursor (zymogen) C1s to C1s, the active enzyme, whose substrates are C4 and C2. The primary question discussed in this paper is evidence that indicates that epitope distribution and density is a major factor in controlling the configuration of antibodies which in turn controls the activation of bound C1. This evidence confirms earlier findings that binding of C1 is a necessary but not sufficient condition for activating C1.

EA3H-C4hu treated with 2-mercaptoethanol (MSH) or dithiothreitol (DTT) were analyzed for residual chains and hemolytic activity. MSH treatment resulted in no loss of the chains of C4b and no loss of reactivity with a polyclonal anti-human C4 rabbit antibody, and the cells did not lose their ability to generate SAC4b2a. DTT-treated cells lost about 70% of the gamma-chain and over 95% of C4b activity; there was no loss of alpha' and beta chains or the ability to react with anti-C4 antibody. Kinetic studies indicated that the remaining 30% of the gamma-chains could not be removed by prolonged incubation with DTT, implying heterogeneity of cell bound C4b. The data also imply that the gamma-chain is important in the generation of SAC4b2a.