Host protective immunity to Trichinella spiralis in mice: activation of Th cell subsets and lymphokine secretion in mice expressing different response phenotypes.

Host protective immunity to the intestinal dwelling nematode Trichinella spiralis is mediated by CD4+ mesenteric lymph node (MLN) cells during the course of intestinal infection. The present study has examined the cytokine production by T cells within the MLN of two H-2-compatible strains of mice infected with T. spiralis which differ in the speed at which they expel the parasite from the gut. For both strains of mice, in vitro stimulation of MLN cells with a protective worm antigen preparation resulted in secretion of elevated levels of interleukin-3 (IL-3), IL-4, IL-5 and IL-9 compared to controls. Negligible levels of interferon-gamma (IFN-gamma) were secreted. Furthermore, a similar pattern of cytokine secretion was observed from MLN cells taken from infected mice after in vitro stimulation by T-cell mitogens. No evidence was found for a relationship between quantity of cytokine secreted and the differences in speed of parasite expulsion in the two strains of mice studied. The results support the hypothesis that protective immunity to T. spiralis infection is associated with the activation of Th2-type cells within the MLN in the relative absence of Th1-type cells.     

Profiles of Th1 and Th2 Cytokines after Primary and Secondary Infection by Schistosoma mansoni in the Semipermissive Rat Host

In contrast to most mouse strains, rats eliminate the primary schistosome burden around 4 weeks postinfection and subsequently develop protective immunity to reinfection. In rat schistosomiasis, we have shown predominant expression of a Th2-type cytokine response at the mRNA level after primary infection. In the present study, we showed a significant increase in interleukin-4 (IL-4) mRNA expression in inguinal lymph nodes early after a secondary infection. IL-5 mRNA expression showed a significant increase at days 2 and 4 postreinfection in the spleen and lymph nodes, respectively. We did not detect any gamma interferon (IFN-gamma) mRNA after a challenge infection. Analysis of cytokine secretion by stimulated spleen cells after a primary infection showed predominant expression of IL-4 with maximum production on day 21, accompanied by production of IL-5 from day 11 to day 67. A significant increase in IFN-gamma secretion was detected at day 21. Analysis of immunoglobulin G2b (IgG2b) and IgG2c (Th1-related isotypes) showed undetectable levels of IgG2b, but detectable levels of specific IgG2c antibodies were observed from day 42. The analysis of Th2-related isotypes showed high specific IgG1 and IgG2a antibody titers from day 29. After a secondary infection, only IL-4 and IL-5 secretion was sustained. This is supported by the increased production of Th2-related isotypes. These findings showed that S. mansoni infection can drive Th2 responses in rats in the absence of egg production which is required to induce a Th2 response in mice and are in favor of the role of Th2-type cytokines in protective immunity against reinfection.     

Induction of T helper 1- and T helper 2-type immune responses during Haemonchus contortus infection in sheep

The production of cytokines by lymphoid cells, isolated from non-infected and Haemonchus contortus-infected lambs, was investigated. Particular attention was paid to differences in T helper 1- (Th1) and Th2-type immune profiles between genetically resistant and random-bred animal groups. Non-infected resistant and random-bred lambs produced equivalent levels of interferon-gamma (IFN-gamma) and interleukin-5 (IL-5), from isolated abomasal lymph node cells (ALN), mesenteric lymph node cells (MLN) and spleen cells (SC), in response to in vitro stimulation with T-cell mitogen (concanavalin A) or larval parasite antigen. ALN and MLN cells derived from infected resistant and random-bred lambs produced relatively lower levels of IFN-gamma, following in vitro stimulation with parasite antigen, when compared with their uninfected counterparts. In contrast, infected lambs of both groups showed enhanced mitogen- and antigen-stimulated production of IL-5, in comparison with uninfected controls, at days 5 and 28 postinfection (p.i.). Mitogen- and antigen-stimulated IL-5 responses were higher among resistant lambs compared with random-bred lambs, with the highest overall production of IL-5 by parasite antigen-stimulated ALN and MLN cells. Among day 28 p.i. lambs, levels of cell culture-derived parasite-specific immunoglobulin G1 (IgG1) and IgE antibodies were higher in resistant lambs than in random-bred lambs, following in vitro stimulation of SC or ALN cells with parasite antigen. Finally, after 28 days p.i., histological examination of abomasal tissue revealed higher densities of mast cells and eosinophils in the mucosa of resistant lambs than in random-bred lambs. Taken together, these data support the notion of a strong Th2-type immune response to Haemonchus infection in genetically resistant sheep, and support the claim for a Th1/Th2 dichotomy in ruminants.     

IgG isotype distribution of local and systemic immune responses induced by influenza virus infection

The IgG isotype profile of the influenza virus-specific immune response was studied by quantitation of serum antibody (Ab) levels in correlation with the enumeration of antibody-secreting cells (ASC) detected in the lung, spleen, mediastinal lymph nodes (MLN), Peyer's patches and bone marrow (BM). Distincst isotypic patterns for serum Ab and Ab produced by cells present at or close to the site of infection were found after primary or repeated infections. An elevated number of IgM ASC was found after primary challenge in the spleen, lung and MLN. In contrast, the site of IgA and IgG production is restricted to the lung and lymph nodes draining the site of infection. In these organs IgA, IgG2a and IgG1 ASC are found as a result of primary virus infection while viral challenge induces mostly activation of IgA-producing cells and secretion of IgA to the lung lavage. In contrast, the majority (80-90%) of Ab detected in the serum belong to the IgG2a subclass and their serum level is maintained at a high level during the whole period of the response. The relative level of virus-specific serum IgG2a in correlation with the production of IgG2a Ab found predominantly in MLN and lung is highly dependent on the viral dose used for priming or challenge. As IgG2a ASC can be detected at relatively low numbers in the spleen and BM these results suggest that the production of the dominant IgG2a isotype of serum Ab occurs close to the viral challenge site. These data, however, point to distinct isotypic regulation in systemic versus local virus-specific Ab responses.     

The induction and migration of antigen-specific helper cells for IgA responses in the intestine.

The distribution of keyhole limpet haemocyanin (KLH)-specific helper cells for antibody responses of IgA, IgM and IgG isotypes in Peyer's patch (PP), mesenteric lymph node (MLN) and peripheral lymph node (PLN) was examined following oral, intraduodenal (ID), intraperitoneal (IP), intra-Peyer's patch (IPP) or subcutaneous (SC) immunization with KLH. Oral or ID immunization gave little or no response in any tissue studied. IP immunization with or without a subsequent ID challenge gave rise to a modest IgA and IgM helper response in MLN but a small IgA and IgM helper response in PP and PLN. IP immunization alone did not stimulate IgG-specific help in any tissues studied, but a small IgG helper response occurred in MLN and PLN after subsequent ID challenge. IPP was the most effective route of immunization, giving rise to a large helper response for IgA, IgM and IgG isotypes in PP, a smaller response in MLN and no response in PLN. The helper response following IPP immunization was not augmented by subsequent ID challenge. SC immunization gave a small but significant helper response for all isotypes in PLN but no response in PP or MLN. The kinetics of the helper response were examined in PP, MLN, PLN and thoracic duct lymph (TDL) following IPP immunization. The helper response for all isotypes in PP was maximal at 2 weeks and then declined. Similar kinetics but of lower magnitude were observed in MLN and TDL. The presence of IgA-specific helper cells in TDL demonstrates that these cells migrate, presumably from GALT, and may constitute an important component of mucosal responses at extraintestinal sites.     

Polyphenolic antioxidants enhance IgE production

Epidemiological data showed that total IgE and IL-4 levels in cigarette smokers were elevated, comparable to those in the asthmatics. The etiological agent(s) elevating IgE production are not clear. We evaluate whether tobacco polyphenols potentiate IgE production in a rodent model. Mice were fed with rutin or CGA in drinking water during antigen sensitization, followed by antigenic challenge i.p. in alum. CGA and rutin were also delivered in a bolus intraperitoneally or intranasally along with antigens during immunization. Antigen-specific IgE and IgG responses were measured. Enhancement of total IgE responses via i.p. and drinking routes can be achieved at concentrations as low as 0.1% CGA. Furthermore, IgG1 responses but not IgG2a and IgG2b were augmented, indicating a Th2 type of response by CGA. Moreover, both antigen-specific and serum IgE production can be achieved when CGA and antigenic challenges were delivered intranasally in the absence of alum. In contrast, nicotine does not enhance antigen-specific IgE production, and only marginally affects serum IgE levels. The more polarized Th2 development in CGA-treated mice may account for enhancement of both antigen-specific and total IgE responses. High levels of IL-4 but not IFN-gamma or IL-12, were observed in antigen-challenged mesenteric lymph nodes (MLN) cultures from CGA-treated mice. In contrast, significant levels of IL-4, IL-12, and IFN-gamma were observed in antigen-challenged cultures from nicotine-treated mice. This study shows that tobacco polyphenols, CGA and rutin potentiated IgE production in vivo. Polyphenolic antioxidants enhance Th2 development. We propose that IgE production and T cell dichotomy may be critically influenced by the redox microenvironment. Enhanced Th2 development and IgE production henceforth may counteract more severe Th1-mediated tissue damage triggered by environmental oxidative stress.     

Terminally differentiated human intestinal B cells. J chain expression of IgA and IgG subclass-producing immunocytes in the distal ileum compared with mesenteric and peripheral lymph nodes

Two-colour immunofluorescence staining for intracellular J chain and IgA (or J chain and IgG) was performed on tissue sections of normal human ileal mucosa (eight adult kidney donors), mesenteric lymph nodes (MLN), peripheral lymph nodes, and palatine tonsils. The most prominent J chain positivity was seen for IgA (97.3%) and IgG (81.7%) immunocytes in the ileal lamina propria (LP). Moreover, the proportion of J chain-expressing extrafollicular immunocytes was significantly higher (P less than 0.05) in MLN than in peripheral lymph nodes for the IgA class (58.5% versus 25.6%); the same proportion for the IgG class was 45.9% versus 30.4%. In clinically normal palatine tonsils of adults, extrafollicular J chain expression was much lower than in peripheral lymph nodes; 14.2% for IgA cells and 5.5% for IgG cells. When related to subclass production, J chain expression was found to be higher for IgA2 than for IgA1 cells in all tissues examined (palatine tonsils excluded because of a small number of IgA2 cells), the difference being significant in MLN and ileal LP (P less than 0.05). The J chain positivity tended to be higher for all IgG subclasses in MLN than in peripheral lymph nodes; this difference was significant (P less than 0.05) for IgG2-producing immunocytes. Taking J chain expression as a marker of clonal immaturity, our results may reflect to some extent distribution of newly generated memory B cell clones from gut-associated lymphoid tissue to MLN, peripheral lymph nodes, and palatine tonsils in a strikingly decreasing order.     

Enhanced immunological tolerance against allograft rejection by oral administration of allogeneic antigen linked to cholera toxin B subunit

A single oral intragastric administration of cholera toxin B subunit (CTB) conjugated to allogeneic thymocytes (ATC, 4 x 10(7) cells) under conditions allowing the CTB to bind the complex to GM1 ganglioside receptors was shown to be efficacious in inducing peripheral T cell tolerance associated with significant suppression of both primary and secondary accelerated rejection of heart allografts when tested in mice. Allogeneic in vivo delayed-type hypersensitivity (DTH), in vitro cytotoxicity responses, and mixed lymphocyte reactions (MLR) by T cells from mesenteric lymph nodes (MLN), popliteal lymph nodes (PLN), and spleen were significantly reduced in mice treated with the CTB-ATC conjugate, as were also the numbers of cells in these organs producing IL-2, IFN-gamma, or IL-4. In contrast, a marked increase in the production of IL-4 in Peyer's patches (PP) and of TGF-beta(1) in PLN was observed. The suppressive potential of T cells from PP and/or MLN after oral treatment with CTB-ATC was further evident by intraperitoneal transfer of such cells from CTB-ATC-treated animals to primed recipients, which led to marked suppression of both allogen-specific DTH and MLR responses. A critical role for PP in inducing peripheral tolerance after oral CTB-ATC treatment was indicated by the absence of tolerance induction in animals whose PP had been destroyed before treatment with CTB-ATC. The results indicate that the protection against allograft rejection by oral treatment with CTB-ATC is mediated by T cells and associated with a strong induction of IL-4 production at mucosal sites and TGF-beta(1) at the effector sites.     

Resistance to Paracoccidioides brasiliensis infection is linked to a preferential Th1 immune response, whereas susceptibility is associated with absence of IFN-gamma production.

The secretion of interferon-gamma (IFN-gamma), interleukin-2 (IL-2), IL-4, IL-5, and IL-10 by antigen-stimulated lymph node cells, eosinophil maturation, and the antibody isotypes produced were examined during intraperitoneal infection of susceptible (B10.A) and resistant (A/Sn) mice with Paracoccidioides brasiliensis. Lymph node cells from resistant mice produced early and sustained levels of IFN-gamma and IL-2, whereas susceptible animals secreted low to undetectable amounts of these type 1 cytokines. Both mouse strains presented late and transient production of IL-4, whereas IL-10 was produced constantly throughout the course of disease. Resistant animals produced increasing levels of IL-5 in the chronic phase of the infection (from the eighth week on), whereas susceptible mice showed two peaks of IL-5 production, at the first and twelfth weeks after infection. Only the susceptible strain presented medullary and splenic eosinophilia concomitant with the raised IL-5 production. In resistant mice, the levels of IgG2a antibodies were significantly higher than those observed in susceptible mice, which preferentially secreted IgG2b and IgA isotypes. Taken together, these results demonstrate that a sustained production of IFN-gamma and IL-2 and a predominant secretion of IgG2a antibodies are associated with resistance to P. brasiliensis. In contrast, the production of low levels of IFN-gamma, early secretion of high levels of IL-5 and IL-10, eosinophilia, and a preferential secretion of IgG2b and IgA isotypes characterize the progressive disease in susceptible animals.     

Lactic dehydrogenase virus infection enhances parasite egg production and inhibits eosinophil and mast cell responses in mice infected with the nematode Nippostrongylus brasiliensis.

The effects of lactic dehydrogenase virus (LDV) infection on the protective immune responses to the nematode Nippostrongylus brasiliensis were studied. Mice with chronic LDV infection showed significantly higher levels of parasite egg production than non-LDV-infected (control) mice after N. brasiliensis infection. Concurrent LDV infection also suppressed peripheral blood eosinophilia and the lung mastocytosis induced by this nematode. LDV infection showed higher expression levels of the interferon-gamma (IFN-gamma) mRNA in lymph nodes compared with control mice before N. brasiliensis infection. In addition, the IgG2a production in LDV-infected mice was higher than that in control mice before and after N. brasiliensis infection. These results suggest that LDV infection modulates protective immune responses against N. brasiliensis infection by the activation of T-helper type 1 cells.     

The use of antibody-secreting cell probes to reveal tissue-restricted immune responses during infection

Antibody secreting cell probes (ASC-probes) were generated from the hepatic lymph node (HLN), mesenteric lymph node (MLN) and spleen of rats after infection with the liver fluke, Fasciola hepatica, and used to probe Western blots of parasite antigens. In chronic primary infections, parasite-specific antibodies were only detected in ASC-probes derived from HLN. Seven days after a secondary infection, a restricted response was detected in ASC-probes from the MLN, directed predominantly against an antigen specific to the newly excysted juvenile (NEJ) stage. This NEJ-specific antigen was only recognized by HLN if the second infection was not rejected and the challenge flukes reached the liver. Measurement of the immunoglobulin levels present in the ASC-probes showed significant elevation only in lymph nodes draining sites of recent infection. In addition, when the isotype profiles were determined in ASC-probes derived from different lymph nodes, it was observed that they showed different isotype preferences, in particular IgA for the MLN, IgE for HLN and IgM for spleen. These results show that discrete and independent immune responses occur in different body compartments of a rat against different stages of a parasite.     

Reduced ratio of protective versus proinflammatory cytokine responses to commensal bacteria in HLA-B27 transgenic rats

Germ-free HLA-B27 transgenic (TG) rats do not develop colitis, but colonization with specific pathogen-free (SPF) bacteria induces colitis accompanied by immune activation. To study host-dependent immune responses to commensal caecal bacteria we investigated cytokine profiles in mesenteric lymph node (MLN) cells from HLA-B27 TG versus nontransgenic (non-TG) littermates after in vitro stimulation with caecal bacterial lysates (CBL). Supernatants from CBL-stimulated unseparated T- or B- cell-depleted MLN cells from HLA-B27 TG and non-TG littermates were analysed for IFN-gamma, IL-12, TNF, IL-10 and TGF-beta production. Our results show that unfractionated TG MLN cells stimulated with CBL produced more IFN-gamma, IL-12 and TNF than did non-TG MLN cells. In contrast, CBL-stimulated non-TG MLN cells produced more IL-10 and TGF-beta. T cell depletion abolished IFN-gamma and decreased IL-12 production, but did not affect IL-10 and TGF-beta production. Conversely, neither IL-10 nor TGF-beta was produced in cultures of B cell-depleted MLN. In addition, CD4(+) T cells enriched from MLN of HLA-B27 TG but not from non-TG rats produced IFN-gamma when cocultured with CBL-pulsed antigen presenting cells from non-TG rats. Interestingly, IL-10 and TGF-beta, but not IFN-gamma, IL-12 and TNF were produced by MLN cells from germ-free TG rats. These results indicate that the colitis that develops in SPF HLA-B27 TG rats is accompanied by activation of IFN-gamma-producing CD4(+) T cells that respond to commensal bacteria. However, B cell cytokine production in response to components of commensal intestinal microorganisms occurs in the absence of intestinal inflammation.     

The temporal relationship among anti-parasite immune elements expressed during the early phase of infection of the rat with Trichinella spiralis

Immunological parameters were measured during the first 20 days of infection with Trichinella spiralis in the rat. Expulsion of adult worms was complete by day 15 postinfection. Eosinophil and neutrophil numbers rose in the blood of infected rats above preinfection levels on days 3 and 6, respectively, and remained high to day 20 postinfection. Release of cytokines by Trichinella-antigen-stimulated mesenteric lymph node cells was measured, and a significant elevation in interferon (IFN)-γ release was detected during the early stage of infection. Although initiated later, interleukin (IL)-10 release showed a pattern similar to IFN-γ. Biphasic release of IL-5 was seen with significant elevation above the preinfection level on day 3 and after day 6 postinfection to the end of the study. IL-4 and IL-2 showed biphasic secretion as well, with the level of IL-4 high in the early and middle part of infection, while the level of IL-2 was detectable only at days 2, 3 and 6 postinfection. Serum anti-parasite IgE rose above preinfection levels after day 6 postinfection. Anti-parasite Ig-positive mesenteric lymph node (MLN) cells were evident by day 3 postinfection for IgM, and day 9 postinfection for IgA and total IgG. The number of Ig-positive MLN cells for all antibody classes returned to preinfection levels by day 20 postinfection. Evaluation of the temporal interactions of the key anti-parasite immune components with which the host engages Trichinella shows a complex interplay between Th1 and Th2 helper subsets. Received: 21 January 1999 / Accepted: 18 February 1999     

The in vitro production of cytokines by mucosal lymphocytes immunized by oral administration of keyhole limpet hemocyanin using cholera toxin as an adjuvant.

The in vitro production of a variety of cytokines by lymphocytes isolated from spleen mesenteric lymph node (MLN), Peyer's patches (PP) and lamina propria (LP) was measured, after oral immunization with keyhole limpet hemocyanin using cholera toxin as an adjuvant. LP responses were characterized by very high levels of interleukin (IL) 4, IL 5 and IL 6 with lower levels of IL 2 and interferon-gamma (IFN-gamma). The PP had lower levels of IL 4, IL 5 and IL 6 than LP but higher levels of IL 2, IFN-gamma was only present at very low levels in this organ. The MLN had a pattern of cytokine production similar to the PP but did produce IFN-gamma. The spleen produced all cytokines measured except IL 5. Antibody production was characterized by IgA in the LP and PP but IgG was the dominant isotype in the spleen, the MLN was a poor source of antibody-producing cells. We interpret the results to show that (a) the LP response to cholera toxin/keyhole limpet hemocyanin is dominated by Th2-type cytokines compared to a lower production of Th1 type and (b) that the PP has responses typical of an organ with a high proportion of resting lymphocytes which develop mainly into Th2-types cells. The spleen is less dominated by Th2-type cytokines than the mucosal sites and this difference is paralleled by IgA antibody production at the mucosal sites and IgG antibody dominance in the spleen.     

Effect of anti-IL-4, interferon-gamma and an antifungal triazole (SCH 42427) in paracoccidioidomycosis: correlation of IgE levels with outcome.

Paracoccidioidomycosis is characterized by depressed cellular but enhanced humoral immune responses, which suggests a Th2 type of response to infection. We investigated possible therapeutic roles for anti-IL-4, interferon-gamma (IFN-gamma) and/or SCH 42427 (SCH), a new triazole antifungal agent, and their effect on serum IgE levels in a murine model of chronic Paracoccidioides brasiliensis infection. BALB/c mice infected by the pulmonary route were studied with three programmes. The subacute model and one acute model experiment investigated cytokine secretion by lymph node cells (LNC), and in a second acute experiment mice were given anti-IL-4, IFN-gamma or nothing 24 h post infection, then killed at 4 weeks. In the chronic model, mice began treatment at 4 weeks post infection, receiving either SCH, IFN-gamma alone, SCH+IFN-gamma, or no treatment for 8 weeks. At 2-week intervals lung and spleen burdens of infection and serum polyclonal IgE levels were determined. In the subacute model (non-progressive infection), initially there was dual production of IL-4 and IFN-gamma by antigen-stimulated LNC. In the acute progressive infection model IL-4, but not IFN-gamma, was secreted. Anti-IL-4 treatment of the acute phase resulted in enhanced host resistance to infection, which correlated with decreased serum IgE. The chronic model, in which the in vivo efficacy of SCH against P. brasiliensis was shown, suggests possible synergy between immunomodulation and antimicrobial chemotherapy (IFN-gamma and SCH). Decreased organ burdens of infection in the chronic model after treatment with SCH, SCH plus IFN-gamma, or anti-IL-4 correlated with decreased serum IgE. These promising novel approaches to treatment of systemic fungal infections suggest a Th2 type of response to P. brasiliensis infection, which can be reversed with successful therapy.     

Dysregulated luminal bacterial antigen-specific T-cell responses and antigen-presenting cell function in HLA-B27 transgenic rats with chronic colitis

HLA-B27/beta2 microglobulin transgenic (TG) rats spontaneously develop T-cell-mediated colitis when colonized with normal commensal bacteria, but remain disease-free under germ-free conditions. We investigated regulation of in vitro T-cell responses to enteric bacterial components. Bacterial lysates prepared from the caecal contents of specific pathogen-free (SPF) rats stimulated interferon-gamma (IFN-gamma) production by TG but not non-TG mesenteric lymph node (MLN) cells. In contrast, essentially equivalent amounts of interleukin-10 (IL-10) were produced by TG and non-TG cells. However, when cells from MLNs of non-TG rats were cocultured with TG MLN cells, no suppression of IFN-gamma production was noted. Both non-TG and TG antigen-presenting cells (APC) pulsed with caecal bacterial lysate were able to induce IFN-gamma production by TG CD4+ cells, although non-TG APC were more efficient than TG APC. Interestingly, the addition of exogenous IL-10 inhibited non-TG APC but not TG APC stimulation of IFN-gamma production by cocultured TG CD4+ lymphocytes. Conversely, in the presence of exogenous IFN-gamma, production of IL-10 was significantly lower in the supernatants of TG compared to non-TG APC cultures. We conclude that commensal luminal bacterial components induce exaggerated in vitro IFN-gamma responses in HLA-B27 TG T cells, which may in turn inhibit the production of regulatory molecules, such as IL-10. Alterations in the production of IFN-gamma, and in responses to this cytokine, as well as possible resistance of TG cells to suppressive regulation could together contribute to the development of chronic colitis in TG rats.     

Various types of Dirofilaria immitis polyproteins selectively induce a Th2-Type immune response

Dirofilaria immitis polyproteins (DiAgs) are found as 15-kDa monomeric and 30-kDa dimeric forms in excretory-secretory products of the adult worm. We evaluated the ability of various types of recombinant DiAg (rDiAg; V1 and V2 as monomers and V1V2, V2V1, V1V1, and V2V2 as dimers) to influence Th1/Th2 immune responses. V1-, V1Vx- and V2-, V2Vx-driven nonspecific immunoglobulin E (IgE) production peaked at 21 and 14 days after administration, respectively. Dimer-induced IgE response was an interesting biphasic pattern with the second peaks on days 35 (V2Vx) or 42 (V1Vx). Absolute amounts of nonspecific IgE production induced with monomers were larger than those observed with dimers at the first peak. The magnitude of cell expansion and interleukin-10 (IL-10) production in mesenteric lymph node (MLN) B-cell induced with rDiAgs was linked to the levels of the first IgE peak in vivo and IgE produced by rDiAg plus IL-4-stimulated B cells in vitro. All rDiAgs failed to augment IgG2c production. V2 and V2Vx elicited IL-4 production by MLN cells more rapidly than V1 and V1Vx. The inhibitory effect of rDiAg on gamma interferon (IFN-gamma) production was stronger in monomers than in dimers. Neutralization of IL-10 restored IFN-gamma production, whereas the expression of IL-4 and IgE was partly prevented by depletion of IL-10. These results indicate that monomer rather than dimer is an efficient form of DiAg and suggest that the difference of IgE-inducing capacity among these DiAgs is closely associated with the pattern of both B-cell activation and IL-4 production.     

The enumeration of rat IgE-secreting cells using a reverse plaque-forming cell assay.

A reverse hemolytic plaque assay utilizing protein A-coated sheep red cells and a specific rabbit anti-rat IgE preparation has been adapted for the enumeration of rat IgE-secreting cells derived from the IR-162 rat plasmacytoma and from rats infected with Nippostrongylus brasiliensis. Under optimal conditions, approximately 10-15% of the viable plasmacytoma cells were scored as plaque-forming cells. In rats infected with 5000 Nippostrongylus brasiliensis larvae, a maximum of 2 x 10(6) IgE-secreting cells were found in the mesenteric lymph nodes, and no IgE plaque-forming cells in their spleens. The kinetics of the mesenteric lymph node plaque-forming cell responses closely coincided with total serum IgE levels, with maximum responses occurring 15-16 days after infection. There was a high degree of correlation between the mesenteric lymph node IgE plaque-forming cell responses and total serum IgE levels of individuals rats. It was concluded that the IgE-secreting cells in the mesenteric lymph nodes contributed, in a large way, to the elevated levels of IgE found in the circulation of these rats.