Accumulation of eosinophils in intestine-draining mesenteric lymph nodes occurs after Trichuris muris infection

Eosinophils have recently been demonstrated capable of localizing to lymph nodes that drain mucosal surfaces, in particular during T helper 2 (Th2) responses. Resistance of mice to infection with the gastrointestinal nematode Trichuris muris depends critically on mounting of a Th2 response and represents a useful model system to investigate Th2 responses. Following infection of resistant BALB/c mice with T. muris, we observed accumulation of eosinophils in intestine-draining mesenteric lymph nodes (MLNs). The accumulation of MLN eosinophils was initiated during the second week of infection and peaked during worm expulsion. In contrast, we detected a comparably late and modest increase in eosinophil numbers in the MLNs of infected susceptible AKR mice. MLN eosinophils localized preferentially to the medullary region of the lymph node, displayed an activated phenotype and contributed to the interleukin-4 (IL-4) response in the MLN. Despite this, mice genetically deficient in eosinophils efficiently generated IL-4-expressing CD4(+) T cells, produced Th2 cytokines and mediated worm expulsion during primary T. muris infection. Thus, IL-4-expressing eosinophils accumulate in MLNs of T. muris-infected BALB/c mice but are dispensable for worm expulsion and generation of Th2 responses, suggesting a distinct or subtle role of MLN eosinophils in the immune response to T. muris infection.     

CTLA-4 regulates the murine immune response to Trypanosoma cruzi infection

Infection with Trypanosoma cruzi causes a profound suppression of T cell responsiveness to polyclonal or antigenic stimuli. In this study, we quantified expression of the negative T cell regulatory molecule CTLA-4 in T. cruzi infected mice and analysed its influence on the immune suppression. Levels of splenic CTLA-4 expression were highest around day 10 after infection, reaching 5% in resistant B6D2F1 mice, but exceeding 10% of CD4(+) T cells in C57BL/6 mice that were susceptible to mortal disease. The proliferative response of explanted splenocytes to CD3-mediated stimulation was strongly suppressed in both the susceptible and the resistant strains. Blockade of CTLA-4 in vitro with a monoclonal antibody affected neither proliferative response nor cytokine production (IFN-gamma, IL-4 and IL-2) by splenic T cells from infected C57BL/6 mice. Treatment of mice with anti-CTLA-4 antibody on the day of infection decreased IFN-gamma production and reduced mortality by about 50%. We conclude that high CTLA-4 expression is a hallmark of severe disease in murine T. cruzi infection, and that CTLA-4 has a regulative influence at the early stages during priming of the immune reaction to the parasite, augmenting a strong Th1-biased response.     

Mechanisms of leucocyte recruitment to the inflamed large intestine: redundancy in integrin and addressin usage

The caecal-dwelling nematode Trichuris muris provides a natural model of human whipworm infection. Resistance to T. muris is dependent on a host Th2 response, and CD4+Th2 cells migrate to the gut-associated lymphoid tissue (GALT) to elicit parasite expulsion. Thus, CD4+T cells infiltrate the caecal lamina propria during infection, along with other leucocyte subsets that are not critical for parasite expulsion, such as eosinophils. Trafficking of leucocytes to the GALT has been shown to be dependent on the alpha4beta7/MAdCAM-1 integrin-addressin interaction. However, where inflammation is present, such as during T. muris infection, redundant mechanisms of leucocyte recruitment may also occur in addition to traditional gut-homing interactions. We utilized an anti-integrin/addressin antibody treatment regime to investigate this redundancy in resistant, T. muris-infected C57BL/6 mice. Where only the alpha4beta7/MAdCAM-1 interaction was blocked, mice remained resistant to T. muris infection, making a Th2 response and both CD4+T cells and eosinophils infiltrated the site of infection. However, in the absence of available alpha4beta7 and alpha4beta1, mice became chronically infected with T. muris and mounted a more Th1-biased immune response. Interestingly, CD4+T cells, but not eosinophils, were able to infiltrate the caecum, showing different levels of redundancy between leucocyte subsets during infection.     

Anti-IL-9 vaccination prevents worm expulsion and blood eosinophilia in Trichuris muris-infected mice

Production of neutralizing anti-IL-9 antibodies was induced in mice by immunization with mouse IL-9 coupled to ovalbumin. In the six mouse strains tested, a strong and long-lasting anti-IL-9 response developed with seric inhibitory titers of 10(-3) to 10(-5), as measured in an in vitro IL-9-dependent cell proliferation assay. In vivo, this immunization completely abrogated the increase in mast-cell protease-1 levels as well as the eosinophilia observed in mice after implantation of an IL-9-secreting tumor. We took advantage of this method to assess the role of IL-9 in infections with nematode Trichuris muris, where IL-9 production correlates with the resistant phenotype. C57BL/6 mice, which normally expel the parasite, became susceptible after anti-IL-9 immunization, demonstrating that IL-9 plays a critical role in this model. In addition, neutralization of IL-9 also inhibited parasite-induced blood eosinophilia. Taken together, the present data demonstrate the potency of our strategy to antagonize IL-9 in vivo and shows that this cytokine plays a major role in resistance against T. muris infection.     

Coimmunization with IL-15 plasmid enhances the longevity of CD8 T cells induced by DNA encoding hepatitis B virus core antigen

AIM: To test the feasibility of delivering a plasmid encoding IL-15 as a DNA vaccine adjuvant for improving the immune responses induced by hepatitis B virus core gene DNA vaccine. METHODS: We used RT-PCR based strategies to develop IL-15 expression constructs. We first confirmed that the gene could be expressed in Escherichia coli due to the poor expression of IL-15. Then the bioactivity of IL-15 plasmid expression product was identified by CTLL-2 proliferation assay. One hundred micrograms of DNA from each of the IL-15 eukaryotic expressed plasmid and the recombinant plasmid harboring DNA encoding the 144 amino acids of the N-terminus of HBV core gene (abbreviated pHBc144) was used to co-immunize C57 BL/6 mice. The titer of anti-HBcIgG was detected by ELISA and the antigen-specific CD8 T cells (CD8 IFN-γ T cells) were detected by intracellular cytokine staining at different time points. RESULTS: After co-immunization by pIL-15 and pHBc144 DNA vaccine the antigen-specific CD8 cells of mice increased gradually, the first peak of immune response appeared 14 d later, then the number of antigen-specific CD8 Ts cells decreased gradually and maintained at a steady level in 3 mo. After boosting, the number of antigen-specific CD8 T cells reached the second peak 10 d later with a double of the 1st peak, then the number of antigen-specific CD8 T cells decreased slowly. IL-15 as a gene adjuvant had no significant effect on humoral immune responses induced by hepatitis B virus core gene DNA vaccine, but increased the memory antigen-specific CD8 T cells induced by hepatitis B virus core gene DNA vaccine. CONCLUSION: DNA vaccine constructed by HBc Ag 1-144 amino acid induces effective cell immunity, and cytokine plasmid-delivered IL-15 enhances the longevity of CD8 T cells.     

Leishmania infantum released proteins specifically regulate cytokine expression and production patterns by CD4+ and CD8+ T cells

Specific immune responses by CD4+ and CD8+ T cells, from two infected mice strains (BALB/c and C57BL/6), induced by High, Inter and Low protein fractions released by Leishmania infantum, were assessed through the evaluation of IL-12, IFN-gamma and IL-10 mRNA by real-time PCR and respective protein production by ELISA. During infection establishment, High and Inter fractions directed both mice strains T cells subsets to increase the production of IFN-gamma, associated to IL-12 release. Later on, parasite replication augmented in BALB/c and stabilised in C57BL/6 mice. Inter fraction induced CD4+ T cells to maintain IFN-gamma production, with the simultaneous release of IL-12 by both cell subsets in BALB/c mice and by CD8+ T cells in C57BL/6 mice. These observations suggested a prophylactic potential for Inter fraction which was able to induce Th1 response with IL-12 involvement, required for the maintenance of memory cells, in mice strains with different parasitic evolution.     

Contrasting effects of Trichinella spiralis and Trichuris muris antigens on the infection by Leishmania infantum in BALB/c mice

The interaction of Trichinella spiralis and Trichuris muris derived antigens with the infection by Leishmania infantum was investigated in BALB/c mice. Infection with 10(6) promastigotes of L. infantum did not induce relevant serum antibody (IgG subclasses), nor cytokine (IFN-gamma, IL-4) responses despite that mice could partially control the infection. Immunization with T. spiralis activated a moderate IgG1 and secondarily an IgG2a anti-leishmanial response whereas immunization with T. muris elicited only a weak and late activation of IgG1 anti-leishmanial response. Immunization with T. muris caused an elevation of serum IFN-gamma levels which was drastically reinforced by the L. infantum infection, and that was accompanied by almost complete parasitological cure of infected mice. Immunization with T. spiralis induced an elevation of serum IL-4 levels but this response was greatly (about 60%) neutralized by the infection with L. infantum, and this was associated to exacerbation of the infection.     

Modulation of cytokine production and response phenotypes in murine trichuriasis

BALB/K mice are usually resistant to infection with the intestinal nematode parasite Trichuris muris and exhibit a Th2 dominated (IL-5, IL-9) response. Conversely in B10.BR mice, which are unable to expel T. muris, Th1 type (IFN-gamma producing) cells predominate. We have manipulated the course of infection in these two strains of mice such that the period of host-parasite contact is extended in the former and curtailed in the latter. Extension of host-parasite contact in BALB/K mice beyond normal (day 21) resulted in the modulation of cytokines produced by in vitro concanavalin A (Con-A) stimulated MLNC away from IL-5 and IL-9 (Th2-type cytokines) in favour of the Th1-type cytokine IFN-gamma. Curtailment of host parasite contact in B10.BR mice to less than 21 days resulted in elevated production of IL-5 and IL-9 by MLNC in the absence of elevated IFN-gamma levels. Thus modulation of expulsion phenotype also modulates cytokine production by T-cells in the MLN draining the site of infection, with a Th2 response being associated with resistance and a Th1 type response with the inability to expel the parasite. Mechanisms by which the modulated cytokine profiles arise are discussed.     

CD4+ and/or gammadelta+ T cells in the liver spontaneously produce IL-4 in vitro during the early phase of Leishmania major infection in susceptible BALB/c mice.

Numerous studies on the cytokine production profile in Leishmania major infected susceptible and resistant mice have been carried out to elucidate the mechanisms of healing or non-healing of this infection. However, many methods may have failed to detect the actual cytokine production in the inflammatory foci. To overcome this problems, the ELISPOT assay was used to examine the spontaneous production of IL-4 and IFN-gamma in vitro by mononuclear cells from the spleen, lymph nodes and liver in L. major-infected susceptible BALB/c and resistant C57BL/6 mice. None of these mononuclear cells spontaneously produced IFN-gamma in either mouse strains in vitro in the absence of the corresponding antigen(s). However, liver mononuclear cells from infected BALB/c mice spontaneously produced IL-4 in vitro in as early as 2 weeks after the infection, but this was not observed in C57BL/6 mice. The IL-4 producing liver lymphocytes consisted of CD4+ and/or gammadelta+ T cells and uncharacterized cells. These results suggest that liver lymphocytes play some role in the establishment of Th2 prevalence in susceptible BALB/c mice, based on the importance of IL.4 production in the early phase of L. major infection in establishing Th2 dominance in this parasite susceptible mouse.     

Increased interleukin-4, interleukin-5, and interferon-gamma in airway CD4+ and CD8+ T cells in atopic asthma

Increased Th2 cytokine production in asthma is widely accepted, but excess production by asthmatic human airway CD4(+) T cells has not been demonstrated, nor has a relationship with disease severity. The importance of airway CD8(+) T cell type 1 and type 2 cytokine production in asthma is unknown. We investigated frequencies of IFN-gamma, interleukin (IL)-4 and IL-5 producing CD4(+) and CD8(+) blood and sputum T cells from normal subjects and subjects with asthma and compared between cell subsets, subject groups, and body compartments with and without in vitro stimulation and investigated relationships between cytokine production and asthma severity. Production of IL-4, IL-5, and IFN-gamma by unstimulated sputum CD4(+) and CD8(+) T cells was increased in subjects with asthma and related to disease severity, more for CD8(+) than for CD4(+) T cells. Frequencies of sputum CD8(+) T cells producing type 1 and type 2 cytokines were similar to those of CD4(+) T cells. In vitro stimulation polarized peripheral blood cytokine production toward IFN-gamma production, significantly more in subjects with asthma than in normal subjects. These data demonstrate increased type 1 and 2 cytokine production in CD4(+) and CD8(+) T cells in sputum and relate production to disease severity. Findings in blood did not reflect those in airways.     

Interleukin-18 stimulates hematopoietic cytokine and growth factor formation and augments circulating granulocytes in mice

Because interleukin-18 (IL-18) is similar to IL-1 and is known to be involved in the hematopoietic progenitor cell growth, the effect of IL-18 on circulating cell populations was examined. Repeated administration of IL-18 induced significant amounts of neutrophilia in mice. In parallel, high levels of interferon-gamma (IFN-gamma), IL-6, and granulocyte-macrophage colony-stimulating factor (GM-CSF) were detected in the serum of these mice. Interestingly, the cytokine profiles as well as the cell populations in circulation altered around 2 weeks after the beginning of IL-18 administration. A weak but definite eosinophilia was observed concurrently with the appearance of serum IL-5. Consistent with these observations, IL-18 induced secretion of IFN-gamma, GM-CSF, and IL-6 from splenocytes in culture. IL-18 also induced low levels of IL-5 in the splenocyte culture, which was inhibited by IL-12. However, markedly high levels of IL-5 were secreted into the culture medium when splenocytes from IFN-gamma-deficient mice were stimulated by IL-18. CD4(+) T cells strongly responded to IL-18 to secrete IL-5 and GM-CSF. IL-18 stimulated secretion of IL-6 and expression of G-CSF mRNA in splenic adherent cells. Expression of IL-18 receptors was detected in CD4(+) T cells and splenic adherent cells (macrophages). These results show that IL-18 stimulates CD4(+) T cells and macrophages to secrete IL-5, GM-CSF, IL-6, and granulocyte-colony stimulating factor in the absence of IL-12, which in turn induces hematopoietic cell proliferation causing neutrophilia and eosinophilia in mice.     

Isolates of Trichuris muris elicit different adaptive immune responses in their murine host

The J and S isolates of Trichuris muris have different infection profiles in C57BL/6 mice; J worms are expelled, S worms survive to chronicity. Building on this, the ability of the J and S isolates to survive, and the quality of the immune response induced was explored in three different strains of mouse. The resistant BALB/c mouse mounted a strong Th2 response against both isolates, which were quickly expelled. The susceptible AKR host mounted a Th1 response and retained both isolates. Despite equivalent worm exposure, mesenteric lymph node cells from AKR mice infected with the S isolate produced significantly higher levels of IL-12 and the intestinal mastocytosis was reduced. IgG1 and IgG2a from S-infected AKR mice recognized low molecular weight antigens not recognized by J-infected mice. Differential expulsion kinetics was observed in the slower-responding C57BL/6 strain; J worms were expelled but S isolate worms were retained. Survival of the S isolate was again associated with elevated IL-12 and decreased Th2 responses. In resistant mouse strains, the outcome of infection is thus dominantly influenced by host genetics. However, in the slower-responding host, isolate-derived factors may play a role in shaping the quality of the adaptive immune response, thus influencing parasite survival.     

T cell cytokine imbalance towards production of IFN-gamma and IL-10 in NZB/W F1 lupus-prone mice is associated with autoantibody levels and nephritis

OBJECTIVE: The role of T cell-derived cytokine production in lupus is poorly understood. We analysed the cytokine production of CD4(+) T cells in the NZB/W F1 mouse strain, the mouse model probably most closely resembling human systemic lupus erythematosus (SLE), and assessed whether a possible shift in the cytokines expressed is associated with age or disease activity. METHODS: We used intracellular cytokine staining and flow cytometry to determine the cytokine expression of splenic CD4(+) T cells for interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), interleukin-4 (IL-4) and IL-10. NZB/W F1 mice at different ages spanning 5 to 36 weeks were analysed, healthy Balb/cxNZW F1 (CWF1) mice were used as controls. Serum anti-double-stranded DNA (anti-dsDNA) antibody levels were determined by enzyme-linked immunosorbent assay (ELISA), and proteinuria and plasma creatinine were estimated using commercial test kits. RESULTS: The cytokine profile of CD4(+) T cells was shifted towards T-helper 1 (Th1) cells and the frequencies of Th cells expressing IFN-gamma(+) correlated with age, anti-dsDNA-immunoglobulin G (IgG) titre and proteinuria. An increased percentage of IL-10 producers correlated positively with anti-dsDNA-IgG and proteinuria, and a small gain in IL-4 producers correlated with plasma creatinine. Neither the percentage of IL-10 producers nor IL-4 producers showed a significant correlation with age. There was no significant change observed in the frequency of TNF-alpha T cells. The IFN-gamma/IL-4 ratio demonstrated an increasing shift towards a Th1-type response during disease development that was not present in healthy mouse strains. CONCLUSION: The association between the frequencies of T cells expressing IFN-gamma and IL-10 and clinical findings suggests a key role for these cells in the pathogenesis of lupus.     

Cytokines and antibody responses during Trypanosoma congolense infections in two inbred mouse strains that differ in resistance

We studied IL-4, IL-10 and IFN-gamma secretion by splenocytes and the plasma levels of different isotypes of antibodies against various antigens of Trypanosoma congolense in highly susceptible BALB/c and relatively resistant C57BL/6 mice during the early course of infection with T. congolense. The patterns of appearance of cytokine spotforming cells in the spleens were essentially similar in the two mouse strains although higher numbers were detected in the spleens of BALB/c than C57BL/6 mice on some days post-infection. However, the amount of IL-4, IL-10 and IFN-gamma secreted into the culture fluids was dramatically different. From day 4 forward, splenocytes from BALB/c mice secreted very high levels of these cytokines. In contrast, splenocytes from infected C57BL/6 mice did not secrete detectable levels of IL-4 throughout the period tested. The secretion of IL-10 and IFN-gamma by C57BL/6 splenocytes only became appreciable on day 6 and was down-regulated by day 8, when the first wave of parasitaemia was being controlled. At days 6-8, splenocytes from infected C57BL/6 mice secreted two-fold higher amounts of IL-12 p40 than those from BALB/c mice. Infected BALB/c mice mounted an earlier IgM antibody response to variant surface glycoprotein (VSG), formalin-fixed T. congolense and whole T. congolense lysates than did infected C57BL/6 mice. However, they failed to make any detectable IgG3 and IgG2a antibody responses to these antigens whereas infected C57BL/6 mice made strong IgG3 and IgG2a responses. We speculate that enhanced resistance against T. congolense infections in mice may be mediated by IL-12 dependent synthesis of IgG2 antibodies to VSG and possibly also common trypanosomal antigens.     

Role of T cells in innate and adaptive immunity against murine Burkholderia pseudomallei infection

Antigen-specific T cells are important sources of interferon (IFN)-gamma for acquired immunity to intracellular pathogens, but they can also produce IFN- gamma directly via a "bystander" activation pathway in response to proinflammatory cytokines. We investigated the in vivo role of cytokine- versus antigen-mediated T cell activation in resistance to the pathogenic bacterium Burkholderia pseudomallei. IFN-gamma, interleukin (IL)-12, and IL-18 were essential for initial bacterial control in infected mice. B. pseudomallei infection rapidly generated a potent IFN-gamma response from natural killer (NK) cells, NK T cells, conventional T cells, and other cell types within 16 h after infection, in an IL-12- and IL-18-dependent manner. However, early T cell- and NK cell-derived IFN-gamma responses were functionally redundant in cell depletion studies, with IFN-gamma produced by other cell types, such as major histocompatibility complex class II(int) F4/80(+) macrophages being sufficient for initial resistance. In contrast, B. pseudomallei-specific CD4(+) T cells played an important role during the later stage of infection. Thus, the T cell response to primary B. pseudomallei infection is biphasic, an early cytokine-induced phase in which T cells appear to be functionally redundant for initial bacterial clearance, followed by a later antigen-induced phase in which B. pseudomallei-specific T cells, in particular CD4(+) T cells, are important for host resistance.     

Age-related alteration of cytokine production profile by T cell subsets in mice: a flow cytometric study.

Spleen cells from young and old C57BL/6 mice were stimulated with a combination of anti-CD3 and anti-CD28 antibodies, and the profile of cytokine production was examined by two different methods; the concentrations of cytokines as measured by ELISA, and identification of cytokine-positive cells by flow cytometry. The ELISA method revealed that IL-2 production by spleen cells after stimulation was significantly lower in the old mice compared to the young mice. while IFN-gamma production was the reverse. The flow cytometric analysis showed that the percentage of IL-2 positive cells in spleen cells after the stimulation was significantly lower in the older mice than in the young mice, and vice versa for the percentage of IFN-gamma-positive cells. Regarding the T cell subsets, CD4+ T cells were a major source of IL-2 in both the young and old mice. IL-2-positive cells in both CD4+ and CD8+ T cells showed a significant decrease with age. On the contrary, CDX T cells were the major source of IFN-gamma. An age-related increase of IFN-gamma positive cells was observed in both CD4+ and CD8+ T cells. CD4 T cells were the major source of IL-4, and the percentage of IL-4-positive CD4+ T cells also increased with age, although the level of IL-4 production was modest in C57BL/6 mice compared with IL-2 and IFN-gamma. Such age-related changes of cytokine production are presumed to play an important role in the alteration of immunological capacity with age.     

A critical role for neutrophils in resistance to experimental infection with Burkholderia pseudomallei

Inhalation is an important route of infection with Burkholderia pseudomallei, the causative agent of melioidosis. In resistant C57BL/6 mice, activated neutrophils are rapidly recruited to the lungs after intranasal B. pseudomallei infection. Prevention of this response by use of the anti-Gr-1+ cell-depleting monoclonal antibody RB6-8C5 severely exacerbated disease, resulting in an acute lethal infection associated with a 1000-fold increase in lung bacterial loads within 4 days. C57BL/6 interferon (IFN)-gamma(-/-) mice were also acutely susceptible to pulmonary B. pseudomallei infection, dying within 3 days of challenge; this suggests that IFN-gamma is essential for control in the lungs and precedes the protective role of neutrophils in resistance. In neutrophil-depleted mice, lung concentrations of tumor necrosis factor (TNF)-alpha, IFN-gamma, and interleukin-6 were decreased by up to 98%. Natural killer cells were the principle source of IFN-gamma, and monocytes were the principle source of TNF-alpha, suggesting that neutrophils play an important indirect role in the generation of the early cytokine environment in the lungs.     

T cells in the liver: there is life beyond the graveyard

Influenza A virus infection of C57BL/6 mice is a well-characterized model for studying CD8+ T cell-mediated immunity. Analysis of primary and secondary responses showed that the liver is highly enriched for CD8+ T cells specific for the immunodominant H2D(b)NP(366-374) (D(b)NP(366)) epitope. Functional analysis established that these liver-derived virus-specific CD8+ T cells are fully competent cytotoxic effectors and IFN-gamma secretors. In addition, flow cytometric analysis of early apoptotic cells showed that these influenza-specific CD8+ T cells from liver are as viable as those in the spleen, bronchoalveolar lavage, mediastinal lymph nodes, or lung. Moreover, cytokine profiles of the influenza-specific CD8+ T cells recovered from different sites were consistent with the bronchoalveolar lavage, rather than liver population, being the most susceptible to activation-induced cell death. Importantly, adoptively transferred influenza virus-specific CD8+ T cells from the liver survived and were readily recalled after virus challenge. Together, these results show clearly that the liver is not a "graveyard" for influenza virus-specific CD8+ T cells.     

Immunity to coccidiosis: genetic influences on lymphocyte and cytokine responses to infection with Eimeria vermiformis in inbred mice

Cellular and cytokine responses to infection with Eimeria vermiformis were compared in BALB/c (resistant) and C57BL/6 (B6-susceptible) inbred mice. Cellular responses in the mesenteric lymph node (MLN) occurred sooner after primary infection in the resistant BALB/c strain. In contrast, proliferative responses occurred earlier after challenge in B6 mice. Resting levels of CD4 + ve and CD8 + ve T-lymphocytes in the MLN differed between the two strains but the relative numbers of each subset remained relatively constant throughout primary infection. MLN cells taken at intervals after infection were assayed for release of the cytokines IFN-gamma, IL-5 and IL-10 after culture in vitro with the mitogen Concanavalin A (Con-A) or with parasite antigen. With either stimulus cells from resistant BALB/c mice released IFN-gamma and IL-5 earlier after infection than did B6 cells. The strains had a comparable absolute ability to produce IFN-gamma but BALB/c cells released more IL-5 than did B6, levels declining, rather than increasing, during primary infection in the latter. Only cells from BALB/c mice released IL-10 during infection. Cells taken after a secondary infection released relatively little cytokine after pulsing in vitro. These data suggest that the difference in response phenotype between the two strains when infected with E. vermiformis reflect a kinetic, rather than a qualitative, difference in ability to mount protective T-helper (Th) cell subset responses. No evidence was found for a Th2-mediated interference with ability to release IFN-gamma, the cytokine most closely associated with protective immunity.