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The binding of IgE to high-affinity IgE receptors (Fc epsilon RI) on the surface of mast cells and basophils primes these cells to secrete a panel of proinflammatory mediators upon subsequent exposure to specific Ag. We now find that the level of Fc epsilon RI expression on bone marrow basophils in mice infected with the nematode Strongyloides venezuelensis exhibits a strong positive correlation with the serum concentration of IgE, as was previously reported for human blood basophils. Moreover, the administration of IgE in vivo can significantly upregulate Fc epsilon RI expression on mouse basophils, and genetically IgE-deficient (IgE -/-) mice exhibit a dramatic (approximately 81%) reduction of basophil Fc epsilon RI expression compared with the corresponding normal (IgE +/+) mice. The finding that IgE can be a major regulator of mouse basophil Fc epsilon RI expression in vivo identifies a potentially important mechanism for enhancing the expression of effector cell function in IgE-dependent allergic reactions or immunologic responses to parasites.

The binding of immunoglobulin E (IgE) to high affinity IgE receptors (Fc(epsilon)RI) expressed on the surface of mast cells primes these cells to secrete, upon subsequent exposure to specific antigen, a panel of proinflammatory mediators, which includes cytokines that can also have immunoregulatory activities. This IgE- and antigen-specific mast cell activation and mediator production is thought to be critical to the pathogenesis of allergic disorders, such as anaphylaxis and asthma, and also contributes to host defense against parasites. We now report that exposure to IgE results in a striking (up to 32-fold) upregulation of surface expression of Fc(epsilon)RI on mouse mast cells in vitro or in vivo. Moreover, baseline levels of Fc(epsilon)RI expression on peritoneal mast cells from genetically IgE-deficient (IgE -/-) mice are dramatically reduced (by approximately 83%) compared with those on cells from the corresponding normal mice. In vitro studies indicate that the IgE-dependent upregulation of mouse mast cell Fc(epsilon)RI expression has two components: an early cycloheximide-insensitive phase, followed by a later and more sustained component that is highly sensitive to inhibition by cycloheximide. In turn, IgE-dependent upregulation of Fc(epsilon)RI expression significantly enhances the ability of mouse mast cells to release serotonin, interleukin-6 (IL-6), and IL-4 in response to challenge with IgE and specific antigen. The demonstration that IgE-dependent enhancement of mast cell Fc(epsilon)RI expression permits mast cells to respond to antigen challenge with increased production of proinflammatory and immunoregulatory mediators provides new insights into both the pathogenesis of allergic diseases and the regulation of protective host responses to parasites.

In vitro studies have established that Ig isotype switching typically involves deletion of CH genes that are located between VDJ and the CH gene that will be expressed, and is preceded by transcription of a germline (g) form of that CH gene. Increases in g epsilon transcript levels are induced by the cytokine IL-4, and always precede switching to IgE. To evaluate whether a similar relationship occurs in vivo, we examined IL-4 mRNA, g epsilon RNA, productive (p) epsilon mRNA, and serum IgE levels in two in vivo systems: one in which the injection of anti-IgD antibody induces mIgD+ B cells to switch to the expression of IgE and to secrete this isotype, and a second in which the injection of anti-IgE antibody stimulates IgE secretion by B cells that had been induced to express membrane IgE by earlier treatment with anti-IgD antibody. Increases in IL-4 transcript levels in anti-IgD-injected mice were followed within 24 h by increases in g epsilon RNA, and, one to two days later, by increased p epsilon mRNA and serum IgE levels. IL-4 antagonists blocked the g epsilon and p epsilon RNA and serum IgE responses in these mice, whereas the injection of otherwise untreated mice with IL-4 stimulated, within 24 h, a large increase in g epsilon RNA levels, followed 1-2 days later by a small increase in p epsilon mRNA. Injection of anti-IgD-primed mice with anti-IgE antibody also stimulated increases in IL-4, g epsilon and p epsilon RNA levels; however, the increases in IL-4 and g epsilon RNA were considerably smaller, and the increases in p epsilon mRNA and serum IgE considerably larger, than those observed in anti-IgD antibody-injected mice. IL-4 antagonists blocked the anti-IgE antibody-induced g epsilon RNA response, but not the p epsilon mRNA or serum IgE responses. Thus, IL-4 is required for the induction of g epsilon RNA in at least two in vivo systems, increased g epsilon RNA levels precede increases in p epsilon RNA levels in vivo as in vitro, and neither IL-4 nor g epsilon RNA is required to induce B cells that have already switched to IgE expression to differentiate into IgE-secreting cells.

Oral inoculation of BALB/c mice with infective larvae of Heligmosomoides polygyrus resulted in chronic infection characterized by the release of parasite eggs in the feces for several months. The actual number of eggs per gram of feces was dependent on the dose of the inoculum. Serum IgE in infected mice peaked at a level of greater than 70 micrograms/ml during Weeks 3 through 6 following inoculation, and high levels of IgE (greater than 40 micrograms/ml) persisted for over 14 weeks. Protective immune responses resulted in reduced egg production and the development of markedly fewer adult worms in the small intestines following a challenge inoculation. The role of CD4+ and CD8+ T cells in these responses was examined by depletion in vivo of either T cell subpopulation with rat mAb specific for the appropriate determinants. Mice treated with anti-CD4 during a primary infection had increased EPG which was due primarily to an increase in worm fecundity (eggs produced per adult female). A challenge inoculation of mice that had been cleared of the primary infection with an anthelmintic drug induced a protective response that reduced development of new adult worms by 70-80% and their fecundity by greater than 90%. This protective response was abrogated by injection of mice with anti-CD4. Serum IgE diminished when adult worms were removed after anthelmintic treatment. A more precipitous drop in serum IgE followed successive treatments of mice with an anthelmintic and anti-CD4. In addition, the anamnestic serum IgE response to a challenge inoculation was reduced by over 80% in anti-CD4-treated mice. Anti-CD8 treatment had no appreciable effect on the immunological or parasitological parameters measured following a challenge inoculation with H. polygyrus. Thus, CD4+ T cells regulate host protective immunity, worm fecundity, and IgE levels in an H. polygyrus infection. This experimental system may be particularly suitable for analysis of chronic nematode infections of humans and livestock because of the responsiveness of the parasite in vivo to changes in host immune function.

IL-4 has been shown to induce B lymphocytes to switch from the expression of membrane IgM to the expression of membrane IgE and to be required for the generation of primary polyclonal and secondary Ag-specific IgE responses in mice. To further define the role of IL-4 in the generation of memory IgE responses, we investigated the ability of a combination of anti-IL-4 and anti-IL-4R mAb to block the generation of secondary IgE responses induced by: 1) a second infection with the nematode parasites Nippostrongylus brasiliensis or Heligmosomoides polygyrus; or 2) injection of anti-IgD antibody-primed mice with anti-IgE antibody. The latter stimulus was designed to induce intrinsic membrane IgE-expressing B cells to differentiate into IgE-secreting cells. Although the IgE responses induced by a second nematode infection were completely inhibited by the combination of anti-IL-4 and anti-IL-4R mAb, anti-IgE antibody-induced IgE responses in anti-IgD primed mice were not inhibited by these antibodies to a large degree. Additional experiments demonstrated that the anti-IgE antibody-induced memory IgE response was dependent on CD4+ T cells but did not involve the low affinity B cell Fc epsilon RII. Taken together, these observations provide evidence that IL-4 is required for virgin B lymphocytes to develop into IgE-expressing cells, but is not required for B cells that express intrinsic membrane IgE to differentiate into IgE-secreting cells in a T-dependent response. Furthermore, these data suggest that secondary IgE responses in the parasite models that we have studied develop from B cells that had not previously switched to the expression of IgE.

Although the cytokine interleukin 4 (IL-4) stimulates LPS-activated mouse B lymphocytes to secrete both IgG1 and IgE, an anti-IL-4 antibody completely inhibits IgE responses but has little or no effect on several in vivo IgG responses. IL-4 might, therefore, have a restricted role in the generation of in vivo humoral immune responses. Alternatively, IgG1 responses might be stimulated by IL-4 secreted by T cells that are interacting directly with B cells, so that anti-IL-4 antibody cannot neutralize IL-4 before it binds to a B cell IL-4 receptor. In contrast, an antibody that blocks the IL-4 receptor (IL-4R) should equally inhibit responses to IL-4 produced proximal to or distant from a B cell. This reasoning led us to determine the ability of an anti-IL-4R mAb to affect antibody production in mice injected with a goat antibody to mouse IgD (GaM delta) or inoculated with the nematode parasite Heligmosomoides polygyrus. Anti-IL-4R mAb, like anti-IL-4 mAb, blocked IgE responses by greater than 95% and enhanced IgG2a responses to a variable extent. Anti-IL-4R mAb, however, had only a modest and variable inhibitory effect on the induction of IgG1 responses, although it caused these responses to terminate more rapidly. A combination of anti-IL-4 and anti-IL-4R mAbs totally blocked goat anti-mouse IgD antibody (GaM delta)-induced IgE production but had no additive inhibitory effect on IgG1 production. These observations are most consistent with the view that IL-4 is required for a primary IgE response, but has relatively little role in the induction of IgG1 responses in the in vivo systems studied.

The role of L3T4+ and Lyt-2+ T cells in protective immunity to Nippostrongylus brasiliensis (Nb) was studied in BALB/c mice that were depleted of either the L3T4+ or Lyt-2+ T cell population by injection with rat mAb specific for the appropriate determinant. Host responses to Nb infection including spontaneous elimination of adult worms, development of intestinal mucosal mast cell hyperplasia and the generation of a polyclonal IgE response were all completely blocked by 0.5 mg anti-L3T4 antibody administered simultaneously with Nb inoculation. However, administration of 0.5 mg of anti-Lyt-2 antibody at the same time and 7 days after inoculation with Nb had no effect on any of these responses. Injection of anti-L3T4 antibody as late as 9 days after Nb inoculation interfered with spontaneous cure of Nb infection and anti-L3T4 antibody injection 11 days after Nb inoculation inhibited serum IgE levels measured on day 13 by 50%. In addition, administration of anti-L3T4 antibody at the time of the peak serum IgE response, 13 days after Nb inoculation, accelerated the decline in serum IgE levels. Injection of previously Nb-infected mice with anti-L3T4 antibody at the time of a second Nb inoculation prevented the development of a secondary IgE response but did not affect immunity to Nb infection based on finding no adult worms in the intestines of these mice. These data indicate that 1) L3T4+ T cells are required for spontaneous cure of Nb infection, development of intestinal mucosal mast cell hyperplasia, and the generation and persistence of an IgE response during primary infection with Nb and 2) L3T4+ T cells are required for a considerable time after inoculation for optimal development of these responses. However, L3T4+ T cells are not required for all protective responses in immune mice. In contrast, our data indicate that considerable depletion of the Lyt-2+ T cell population has no significant effect on either worm expulsion or the generation of serum IgE responses.

The possibility that injection of mice with an affinity-purified goat antibody to mouse IgD (GaM delta) that stimulates polyclonal IgG1 secretion might also stimulate differentiation of B cells into IgE-secreting cells was suggested by the observation that such treatment induces T cells from those mice to secrete a lymphokine, B cell stimulatory factor 1 (BSF-1), that can stimulate both IgG1 and IgE secretion in vitro. Studies described in this paper show that injection of BALB/c mice with 200 to 3200 micrograms of GaM delta greatly increased the quantity of splenic epsilon chain-encoding mRNA, the number of spleen cells with cytoplasmic IgE, and the concentration of serum IgE 7 days after injection. Serum IgE levels obtained in these mice were approximately 100 times baseline levels and were comparable with those found in mice infected with the nematode parasite Nippostrongylus brasiliensis, but were approximately 2000-fold less than the peak serum IgG1 levels induced by GaM delta injection. Both IgE and IgG1 secretion in GaM delta injected mice were T dependent (blocked by anti-L3T4 antibody). These observations are consistent with the hypothesis that BSF-1 may play a role in the in vivo stimulation of IgE secretion and provide an easy to apply model for the investigation of in vivo regulation of IgE responses.

The IgE response at the cellular level to helminthic infection was studied in BALB/c mice inoculated with the infective larvae of the nematodes Nippostrongylus brasiliensis (Nb) or Trichinella spiralis (Ts) or with the cercariae of the trematode Schistosoma mansoni (Sm). Changes in mesenteric lymph node (MLN) cell number, cell surface(s) IgD, IgM, IgE and Thy-1.2 and intracytoplasmic (c) IgE were recorded. In addition, a comparable study was conducted in rats infected with Nb. At 11 days after infection (DAI) of mice with Nb or Ts, or rats with Nb, there was a 3-fold increase in cell number in the MNL. There was a marked increase in cell number in the MLN of mice infected with Sm at 7 weeks after infection (WAI) and in the spleens of Sm-infected mice at 4 WAI. The percentage of cIgE+ cells increased from undetectable levels in uninfected mice and rats to as high as 0.5-1.3% in the MLN of helminth-infected mice and rats. Analysis of cell surface molecules with a fluorescence activated cell sorter (FACS) showed that Nb and Ts infection induced slight increases in the percentages of B cells and slight decreases in the percentage of T cells. More remarkably, the percentage of sIgE+ cells in the MLN of both Nb- and Ts-infected mice rose from undetectable levels in uninfected mice to 33 and 27%, respectively, at 15 DAI. This rise was stimulated in Ts-infected mice predominantly by adult Ts. In the MLN of Nb-infected rats, the percentage of cells that were sIgE+ was greater than 50% at 15 DAI. However, there was no detectable increase in sIgE+ cells in the spleen and MLN of Sm-infected mice until 5 WAI; peak levels of approximately 20% sIgE+ cells were reached at 8 WAI. Treatment of MLN cells from mice infected with Nb, Ts or Sm and rats infected with Nb, with pH 4.0 acetate buffer for 1 min (acid treatment) removed all detectable sIgE from greater than 90% of the sIgE+ cells, but did not remove sIgD or sIgM from cells with these surface isotypes. The effect of acid treatment on sIgE was similar even after a secondary infection of mice or rats with nematode larvae. These data show that helminthic infection, in general, is a potent stimulator of the IgE system at the cellular level and that almost all of the sIgE+ cells that arise have acquired cytophilic sIgE.

The lymphokine B-cell stimulatory factor 1 (BSF-1) has been shown to greatly enhance the differentiation of lipopolysaccharide-activated B cells into IgG1- and IgE-secreting cells in vitro. To determine whether in vivo IgG1 and IgE antibody responses are BSF-1 dependent, the ability of a monoclonal rat IgG1 anti-BSF-1 antibody, 11B11, to affect polyclonal IgG1 and IgE production in mice infected with the nematode parasite Nippostrongylus brasiliensis or injected with a purified goat antibody to mouse IgD was studied. 11B11-containing ascites fluid or purified 11B11 strongly inhibited IgE production in both systems but did not affect IgG1 production, while control ascites or normal rat IgG1 had no IgE-inhibitory activity. These results indicate an important physiologic role for BSF-1 in the generation of IgE antibody responses and suggest means for limiting the production of antibodies responsible for allergic reactions without inhibiting protective antibody responses.

The lymphokine IFN-gamma has been shown in vitro to stimulate IgG2a secretion and inhibit IgG1 and IgE secretion by LPS-activated B lymphocytes. To determine whether IFN-gamma has a similar isotype regulatory role in vivo, we studied the abilities of rIFN-gamma and a mAb to IFN-gamma to modify the isotypes of Ig secreted in mice injected with a goat antibody to mouse IgD, which by itself induces large increases in levels of serum IgG1 and IgE and a relatively small increase in serum IgG2a. Multiple injections of IFN-gamma substantially inhibited production of IgG1 and IgE, and stimulated production of IgG2a in affinity purified goat antibody specific for mouse IgD-treated mice; anti-IFN-gamma antibody blocked the effects of IFN-gamma and in fact enhanced IgG1 and IgE secretion and inhibited the IgG2a response in these mice. The role of IFN-gamma in the selection of isotypes of Ig produced in response to injection of mice with the bacterium Brucella abortus (BA) was also studied, because killed, fixed BA are known to stimulate IFN secretion and a predominantly IgG2a antibody response. Anti-IFN-gamma antibody strongly suppressed IgG2a secretion and stimulated IgG1, but not IgE, secretion in BA-immunized mice. BA suppressed IgG1 and IgE secretion and enhanced IgG2a secretion in affinity purified goat antibody specific for mouse IgD-injected mice; treatment of these mice with anti-IFN-gamma antibody reversed the effects of BA on IgG1 and IgG2a secretion, but not the suppressive effect of BA on IgE secretion. These observations demonstrate that IFN-gamma has an important and perhaps unique physiologic role in the stimulation of IgG2a secretion and in the suppression of secretion of IgG1, whereas bacterial antigens can suppress IgE secretion by other mechanisms in addition to IFN-gamma secretion.

To further define requirements for T cell help in the stimulation of an in vivo IgE response, we studied a system in which the injection of mice with a goat antibody to mouse IgD (GaMD) stimulates large polyclonal IgG1 and IgE responses. In this system, both responses are blocked by anti-CD4 antibody, but only the IgE response is blocked by (anti-IL-4) antibody. Anti-CD4 antibody, if injected 5 days after GaMD, was found to inhibit the GaMD-induced IgE response to a much greater extent than the IgG1 response, even though both responses occur simultaneously and are inhibited to an equal extent by optimal or suboptimal doses of anti-CD4 antibody administered 2 days after GaMD. Even a suboptimal, 50-micrograms dose of anti-CD4 antibody, when injected 5 days after GaMD, inhibited the IgE response to a much greater extent than did an optimal 10-mg dose of anti-IL-4 antibody injected at the same time, even though 10 mg of anti-IL-4 antibody more completely inhibited GaMD-induced IgE production than did 50 micrograms of anti-CD4 antibody when injected 2 days after GaMD. These observations provide evidence that a late acting form of T cell help other than IL-4 is important for the generation of an IgE response but not an IgG1 response in GaMD-immunized mice.

We used genetically mast cell-deficient WBB6F1-W/Wv and WCB6F1-S1/S1d mice and the congenic normal (+/+) mice to investigate the effects of intravenous infusion of goat antimouse IgE on heart rate (HR), pulmonary dynamic compliance (Cdyn), pulmonary conductance (GL), and survival. In WBB6F1-+/+ and WCB6F1-+/+ mice, anti-IgE induced extensive degranulation of tracheobronchial mast cells, as well as significant elevation of HR, significant reductions in Cdyn and GL and, in some cases, death. In contrast, W/Wv and S1/S1d mice exhibited little or no pathophysiological responses and no mortality after challenge with anti-IgE. In W/Wv mice reconstituted with mast cells by intravenous administration of bone marrow cells derived from congenic +/+ mice (+/+ BM----W/Wv mice), anti-IgE induced extensive mast cell degranulation, as well as pathophysiological responses and mortality similar to those observed in WBB6F1-+/+ mice. These findings suggest a critical role for mast cells in the development of the cardiopulmonary changes and mortality associated with anti-IgE-induced anaphylaxis.

Recently, it has been reported that in SJA/9 mice infected with Nippostrongylus brasiliensis there are increased numbers of lymphoid cells positive for surface IgM and IgE (sIgM+ and sIgE+) even though they fail to secrete IgE, that both the sIgM and sIgE on these cells are intrinsic, and that there has been no deletion of genes for the Ig heavy chain constant region in these cells. These observations support a nondeletional model for Ig isotype switching. We have now reexamined the nature of sIgE on sIgE+ spleen and mesenteric lymph node cells of N. brasiliensis-infected SJA/9 mice, and the following observations lead us to believe that this sIgE is cytophilic rather than intrinsic: (i) Only approximately 50% of the N. brasiliensis-infected SJA/9 mice have detectable percentages of sIgE+ lymphoid cells. All mice with detectable sIgE+ lymphocytes have lymphocytes positive for intracytoplasmic IgE (cIgE+) and secrete IgE in vitro, while cIgE+ cells and IgE secretion are absent from N. brasiliensis-infected SJA/9 mice that lack sIgE+ cells. (ii) SJA/9 B lymphocytes have receptors for IgE: expression of these receptors is increased in N. brasiliensis-infected mice that have sIgE+ lymphocytes, but not in infected SJA/9 mice that lack sIgE+ lymphocytes. (iii) Treatment of sIgM+ sIgD+ sIgE+ cells for 1 min with dilute acid removes most sIgE but does not affect expression of sIgM or sIgD. (iv) The removal of mouse IgE from sIgE+ B cells facilitates the binding of exogenous rat IgE. (v) The small amount of sIgE that is reexpressed during a period of in vitro culture after acid treatment is blocked by inclusion of exogenous rat IgE in the culture medium. These observations show that most sIgM+ sIgE+ B cells in N. brasiliensis-infected SJA/9 mice do not express intrinsic sIgE; thus studies using these cells to determine mechanisms of Ig isotype switching are inconclusive.

Antibodies of the IgE isotype play a predominant role in immediate hypersensitivity reactions. IL-4, a T cell-derived lymphokine that stimulates increased Ia expression by resting B cells and increased IgG1 secretion by LPS-activated B cells in vitro, has also been shown to regulate in vitro and in vivo polyclonal IgE responses. We report that large quantities of a purified anti-IL-4 mAb inhibit primary in vivo polyclonal IgE responses by 99% in mice infected with Nippostrongylus brasiliensis or injected with anti-IgD antibodies, and totally inhibit secondary Ag-specific IgE responses to TNP-keyhole limpet hemocyanin without effect on either IgG1 or IgG2a responses to these stimuli. The lack of effect of anti-IL-4 antibody on IgG1 secretion cannot be explained simply by inadequate neutralization of IL-4, inasmuch as the doses of anti-IL-4 antibody used blocked an N. brasiliensis-induced increase in B cell Ia expression by more than 85%, whereas in vitro studies indicate that enhancement of B cell Ia expression requires less IL-4 than induction of IgG1 secretion. In addition to demonstrating that IL-4 plays a necessary role in the generation of an in vivo IgE response, we show that IL-4 has an important role in sustaining established IgE responses, because anti-IL-4 antibody, when given at the peak of an N. brasiliensis- or TNP-keyhole limpet hemocyanin-induced IgE response, accelerates the declines in total serum IgE and in IgE anti-TNP antibody levels, respectively. These observations suggest that the effects of IL-4 on in vivo immune responses may be more specific than might have been predicted from in vitro observations, and that regulation of IL-4 production or action may be useful for the prevention or therapy of immediate hypersensitivity disorders.

A flow microfluorometric technique has been developed to analyze IgE receptors on splenic and mesenteric lymph node mononuclear cells from BALB/c mice. Our data show that 1) the binding of DIBADL cross-linked IgE dimers to IgE receptors is specific in that it is inhibited by monomeric rat and mouse IgE but not by mouse or rabbit IgG or by the monoclonal anti-Fc gamma R antibody 2.4G2, and conversely, the binding of DIBADL cross-linked IgG dimers is inhibited by monomeric IgG or 2.4G2 but not by rat or mouse IgE; 2) the binding of IgE dimers is saturable on cells from uninfected and Nippostrongylus brasiliensis (Nb)-infected mice; 3) IgE dimer binding is detectable on most splenic B lymphocytes from uninfected and Nb-infected mice, but not on T lymphocytes from uninfected mice, and on few, if any, T lymphocytes from Nb-infected mice; 4) Nb infection causes a parallel increase in the percentages of B lymphocytes and cells expressing IgE receptors and Fc gamma R; 5) Nb infection leads to a marked increase in B lymphocyte IgE receptor expression, has little if any effect on IgE receptor affinity, and causes only minor changes in Fc gamma R expression; and 6) in vivo activation of B lymphocytes by a goat antibody to mouse IgD decreases IgE receptor expression considerably, but has a minimal effect on Fc gamma R expression. Thus, there are separate receptors for IgE and IgG on murine B lymphocytes, and the effect of Nb infection or anti-IgD treatment on their expression is different.

To determine whether IgE+ cells in the intestinal mucosa of nematode-infected mice were of a mast cell or a lymphocyte lineage, the intestinal mucosae of mast cell-deficient w/wv mice were examined for IgE+ cells after inoculation with Trichinella spiralis muscle-stage larvae. Immunofluorescence staining techniques were used to detect IgE associated with cells in the intestinal mucosa. Comparisons were made among four strains of mice, w/wv (mast cell-deficient), +/+ (normal congenic littermates of w/wv), BALB/c, and SJL, that were either uninfected controls or inoculated with T. spiralis. Tissue sections from the small intestine of T. spiralis-infected BALB/c, SJL, and +/+ mice were fixed in ethanol and were stained with an affinity-purified F(ab')2 rabbit anti-mouse IgE followed by FITC goat anti-rabbit IgG. Large numbers of cells in the intestinal mucosa exhibited bright fluorescence. When other sections of intestines from these mice were processed in Carnoy's fixative and were stained with alcian blue at low pH (a metachromatic stain for mast cells) or alcian blue followed by immunofluorescence staining for IgE, large numbers of mast cells were observed in the intestinal mucosa, and 70 to 90% stained positively for IgE. There was a considerable number of cells in the intestinal mucosa which were IgE+ but which did not stain with alcian blue. Few alcian blue-positive cells and no IgE+ staining cells were present in the intestinal mucosa of control, uninfected +/+, BALB/c, and SJL mice. To determine whether these IgE+ alcian blue-negative cells were of a lymphocyte or a mast cell lineage, the mast cell-deficient w/wv mouse strain was examined after infection with T. spiralis. In contrast to BALB/c, SJL, or +/+ mice, few cells in the intestinal mucosa of T. spiralis-infected w/wv mice stained with alcian blue or were positive for IgE. However, when the IgE response in the MLN of the w/wv mice was compared to the IgE response of BALB/c, SJL, and +/+ mice, numerous IgE+ cells, but no alcian blue-positive cells, were observed in the parenchyma of the MLN from all four strains of T. spiralis-infected mice. In addition, flow microfluorometric analysis of MLN cells stained for surface IgE in suspension showed a comparable proportion of IgE-bearing cells, which were mostly B lymphocytes, among all four strains of T. spiralis-infected mice.(ABSTRACT TRUNCATED AT 400 WORDS)