Th2-type immune response observed in healthy individuals to sonicate antigen prepared from the most prevalent Mycobacterium tuberculosis strain with single copy of IS6110

Different Mycobacterium tuberculosis strains operate different immune evasion strategies for their survival in the host. This mainly depends on the virulence of the strain and the host immune responses. The most virulent strains are actively involved in the transmission, widely spread in the community and induce differential immune responses. We evaluated the immune response of a sonicate antigen prepared from one predominant strain (S7) from M. tuberculosis harbouring a single copy of IS6110. Significant lymphoproliferative response against purified protein derivative from tubercle bacillus (PPD) and H37Rv antigens was observed in PPD positive normal individuals and tuberculosis patients. Interferon-gamma (IFN-gamma) levels against these antigens were significantly increased in normal individuals but not in tuberculosis patients. The antigen S7 showed marginal T-cell proliferation but did not induce IFN-gamma secretion in both groups. Conversely, it induced significantly high levels of cytokine interleukin 4 (IL-4) in normal individuals. The macrophage cytokines, IL-12 and tumour necrosis factor alpha (TNF-alpha), did not show S7 antigen specific stimulation. The intracellular cytokine further confirmed an increase in IL-4(+)/CD4+ T-cells and a decrease in IFN-gamma(+)/CD4+ T-cells upon stimulation. The antibody response showed an increase in IgG and IgA levels against this antigen in normal individuals. These observations suggest that antigen S7 modulates the immune response towards T helper cell type 2 by suppressing T helper cell type 1 protective immune response in PPD positive normal individuals. We speculate that some components of this sonicate antigen are associated with immunosuppressive response.     

Gliadin-specific type 1 regulatory T cells from the intestinal mucosa of treated celiac patients inhibit pathogenic T cells

Celiac disease (CD) results from a permanent intolerance to dietary gluten and is due to a massive T cell-mediated immune response to gliadin, the main component of gluten. In this disease, the regulation of immune responses to dietary gliadin is altered. Herein, we investigated whether IL-10 could modulate anti-gliadin immune responses and whether gliadin-specific type 1 regulatory T (Tr1) cells could be isolated from the intestinal mucosa of CD patients in remission. Short-term T cell lines were generated from jejunal biopsies, either freshly processed or cultured ex vivo with gliadin in the presence or absence of IL-10. Ex vivo stimulation of CD biopsies with gliadin in the presence of IL-10 resulted in suppression of Ag-specific proliferation and cytokine production, indicating that pathogenic T cells are susceptible to IL-10-mediated immune regulation. T cell clones generated from intestinal T cell lines were tested for gliadin specificity by cytokine production and proliferative responses. The majority of gliadin-specific T cell clones had a Th0 cytokine production profile with secretion of IL-2, IL-4, IFN-gamma, and IL-10 and proliferated in response to gliadin. Tr1 cell clones were also isolated. These Tr1 cells were anergic, restricted by DQ2 (a CD-associated HLA), and produced IL-10 and IFN-gamma, but little or no IL-2 or IL-4 upon activation with gliadin or polyclonal stimuli. Importantly, gliadin-specific Tr1 cell clones suppressed proliferation of pathogenic Th0 cells. In conclusion, dietary Ag-specific Tr1 cells are present in the human intestinal mucosa, and strategies to boost their numbers and/or function may offer new therapeutic opportunities to restore gut homeostasis.     

Partial IL-10 inhibition of the cell-mediated immune response in chronic beryllium disease.

Chronic beryllium disease (CBD) provides a human disorder in which to study the delayed type IV hypersensitivity response to persistent Ag that leads to noncaseating pulmonary granuloma formation. We hypothesized that, in CBD, failure of IL-10 to modulate the beryllium-specific, cell-mediated immune response would result in persistent, maximal cytokine production and T lymphocyte proliferation, thus contributing to the development of granulomatous lung disease. To test this hypothesis, we used bronchoalveolar lavage cells from control and CBD subjects to evaluate the beryllium salt-specific production of endogenous IL-10 and the effects of exogenous human rIL-10 (rhIL-10) on HLA expression, on the production of IL-2, IFN-gamma, and TNF-alpha, and on T lymphocyte proliferation. Our data demonstrate that beryllium-stimulated bronchoalveolar lavage cells produce IL-10, and the neutralization of endogenous IL-10 does not increase significantly cytokine production, HLA expression, or T lymphocyte proliferation. Second, the addition of excess exogenous rhIL-10 partially inhibited the beryllium-stimulated production of IL-2, IFN-gamma, and TNF-alpha; however, we measured no change in T lymphocyte proliferation or in the percentage of alveolar macrophages expressing HLA-DP. Interestingly, beryllium salts interfered with an IL-10-stimulated decrease in the percentage of alveolar macrophages expressing HLA-DR. We conclude that, in the CBD-derived, beryllium-stimulated cell-mediated immune response, low levels of endogenous IL-10 have no appreciable effect; exogenous rhIL-10 has a limited effect on cytokine production and no effect on T lymphocyte proliferation or HLA expression.     

Urokinase-type plasminogen activator is required for the generation of a type 1 immune response to pulmonary Cryptococcus neoformans infection.

Urokinase-type plasminogen activator (uPA)(-/-) mice cannot mount protective host defenses during infection with the opportunistic yeast Cryptococcus neoformans (52D). Because effective host defense against C. neoformans requires specific immune responses and the generation of type 1 (T1) cytokines, we determined how the absence of uPA impacts these processes. Wild-type (WT) and uPA(-/-) mice were inoculated with C. neoformans. Macrophage antifungal activity was assessed histologically, T lymphocyte responses in vivo and proliferation in vitro were quantified, and cytokine concentrations were determined by ELISA. uPA(-/-) macrophages have impaired antimicrobial activity. Regional lymph nodes of infected uPA(-/-) mice contained fewer cells than WT, suggesting impaired T cell proliferation in response to the pathogen in vivo. In vitro, uPA(-/-) T lymphocytes had impaired proliferative responses to C. neoformans rechallenge compared with WT. Infected WT mice generated T1 cytokines in the lung, characterized by high levels of IFN-gamma and IL-12. uPA(-/-) mice had decreased levels of IFN-gamma and IL-12, and increased IL-5, a type 2 cytokine. In the absence of uPA, the cytokine profile of regional lymph nodes shifted from a T1 pattern characterized by IFN-gamma and IL-2 to a weak, nonpolarized response. We conclude that in the absence of uPA, lymphocyte proliferative responses are diminished, and mice fail to generate protective T1 cytokines, resulting in impaired antimicrobial activity. This study provides novel evidence that uPA is a critical modulator of immune responses and of immune cell effector functions in vivo.     

Bacillus Calmette-Guérin vaccination of human newborns induces T cells with complex cytokine and phenotypic profiles

The immune response to vaccination with bacillus Calmette-Guérin (BCG), the only tuberculosis vaccine available, has not been fully characterized. We used multiparameter flow cytometry to examine specific T cell cytokine production and phenotypic profiles in blood from 10-wk-old infants routinely vaccinated with BCG at birth. Ex vivo stimulation of whole blood with BCG for 12 h induced expression of predominantly IFN-gamma, IL-2, and TNF-alpha in CD4+ T cells in seven distinct cytokine combinations. IL-4 and IL-10 expression was detected in CD4+ T cells at low frequencies and only in cells that did not coexpress type 1 cytokines. Specific CD8+ T cells were less frequent than CD4+ T cells and produced mainly IFN-gamma and/or IL-2 and less TNF-alpha, IL-4, and IL-10. Importantly, many mycobacteria-specific CD4+ and CD8+ T cells did not produce IFN-gamma. The predominant phenotype of BCG-specific type 1 T cells was that of effector cells, i.e., CD45RA-CCR7-CD27+, which may reflect persistence of Mycobacterium bovis BCG in infants until 10 wk of age. Among five phenotypic patterns of CD4+ T cells, central memory cells were more likely to be IL-2+ and effector cells were more likely to be IFN-gamma+. We concluded that neonatal vaccination with BCG induces T cells with a complex pattern of cytokine expression and phenotypes. Measuring IFN-gamma production alone underestimates the magnitude and complexity of the host cytokine response to BCG vaccination and may not be an optimal readout in studies of BCG and novel tuberculosis vaccination.     

A role for triggering receptor expressed on myeloid cells-1 in host defense during the early-induced and adaptive phases of the immune response

Triggering receptor expressed on myeloid cells (TREM)-1 is a cell surface molecule expressed on neutrophils and monocytes implicated in the propagation of the inflammatory response. To further characterize the function of this molecule in different phases of the immune response, we examined TREM-1 in the context of host defense against microbial pathogens. In primary human monocytes TREM-1 activation did not trigger innate antimicrobial pathways directed against intracellular Mycobacterium tuberculosis, and only minimally improved phagocytosis. However, activation of TREM-1 on monocytes did drive robust production of proinflammatory chemokines such as macrophage inflammatory protein-1alpha and IL-8. Engagement of TREM-1 in combination with microbial ligands that activate Toll-like receptors also synergistically increased production of the proinflammatory cytokines TNF-alpha and GM-CSF, while inhibiting production of IL-10, an anti-inflammatory cytokine. Expression of TREM-1 was up-regulated in response to TLR activation, an effect further enhanced by GM-CSF and TNF-alpha but inhibited by IL-10. Functionally, primary monocytes differentiated into immature dendritic cells following activation through TREM-1, evidenced by higher expression of CD1a, CD86, and MHC class II molecules. These cells had an improved ability to elicit T cell proliferation and production of IFN-gamma. Our data suggest that activation of TREM-1 on monocytes participates during the early-induced and adaptive immune responses involved in host defense against microbial challenges.     

Tumor-derived macrophage migration inhibitory factor (MIF) inhibits T lymphocyte activation

Macrophage migration inhibitory factor (MIF) is a multi-functional cytokine that is considered a pro-inflammatory cytokine. However, our studies show that MIF, when produced in super-physiological levels by a murine neuroblastoma cell line (Neuro-2a) exceeding those normally seen during an immune response, inhibits cytokine-, CD3-, and allo-induced T-cell activation. MIF is also able to inhibit T cells that have already received an activation signal. The T-cell inhibitory effects of culture supernatants from neuroblastoma cells were reversed when the cells were transfected with dicer-generated si-RNA to MIF. When T cells were activated in vitro by co-culture with interleukin (IL)-2 and IL-15 and analyzed for cytokine production in the presence or absence of MIF-containing culture supernatant, inhibition of T-cell proliferation and induced cell death were observed even as the treated T cells produced high levels of interferon-gamma (IFN-gamma). The inhibitory effects of MIF were partially reversed when lymphocytes from IFN-gamma knockout mice were tested. We propose that the high levels of MIF produced by neuroblastoma cause activation induced T-cell death through an IFN-gamma pathway and may eliminate activated T cells from the tumor microenvironment and thus contribute to escape from immune surveillance.     

Sustained expression of CD154 (CD40L) and proinflammatory cytokine production by alloantigen-stimulated umbilical cord blood T cells

Recent data suggests that graft-versus-host disease (GVHD) is initiated by host APCs. Blockade of CD40:CD154 interactions between APCs and T cells in vivo induces T cell tolerance to host alloantigen and dramatically reduces GVHD. Because allogeneic cord blood (CB) transplantation results in a lower incidence and severity of acute GVHD compared with bone marrow transplantation, we have investigated whether CB T cells can express CD154 in response to stimulation by allogeneic monocyte-derived dendritic cells (MDDC) and have used 5- (and 6-)carboxyfluorescein diacetate succinimidyl ester (CFSE) labeling in combination with intracellular cytokine analysis to assess the proliferation and cytokine profiles of alloantigen-responsive cells. CB T cells stimulated with allogeneic MDDC showed stronger proliferation than adult blood T cells. Surface CD154 expression was detected in the actively dividing CFSElow populations of both the CD4+ and CD4- subsets and was brightest in cells that had divided the most. Assessment of supernatants from MDDC-stimulated CB and adult blood T cells showed no significant difference in the levels of either IFN-gamma or TNF-alpha, but CB T cell supernatants did show a significant lack of detectable IL-2. Intracellular cytokine analysis revealed that dividing CB T cells had been primed to produce IFN-gamma, TNF-alpha, and IL-2 on restimulation. Further phenotype analysis showed that 75% of CB T cells producing IFN-gamma were CD8+. These data suggest that MDDC-stimulated CB T cells express functional CD154 and provide enough costimulation for dendritic cells to prime naive CD8+ CB T cells and induce type 1 cytokine production.     

IL-10 inhibits human T cell proliferation and IL-2 production.

Human IL-10 has been reported previously to inhibit the secretion of IFN-gamma in PBMC. In this study, we have found that human IL-10 inhibits T cell proliferation to either mitogen or anti-CD3 mAb in the presence of accessory cells. Inhibited T cell growth by IL-10 was associated with reduced production of IFN-gamma and IL-2. Studies of T cell subset inhibition by human IL-10 showed that CD4+, CD8+, CD45RA high, and CD45RA low cells are all growth inhibited to a similar degree. Dose response experiments demonstrated that IL-10 inhibits secretion of IFN-gamma more readily than T cell proliferation to mitogen. In addition, IL-2 and IL-4 added exogenously to IL-10 suppressed T cell cultures reversed completely the inhibition of T cell proliferation, but had little or no effect on inhibition of IFN-gamma production. Thus, in addition to its previously reported biologic properties, IL-10 inhibits human T cell proliferation and IL-2 production in response to mitogen. Inhibition of IFN-gamma production by IL-10 appears to be independent of the cytokine effect of IL-2 production.     

High IFN-gamma production of individual CD8 T lymphocytes is controlled by CD152 (CTLA-4)

CD8 T cell expansion and cytokine production is needed to generate an effective defense against viral invasion of the host. These features of CD8 T lymphocytes are regulated, especially during primary responses, by positive and negative costimulation. We show in this study that surface expression of CD152 is highly up-regulated on activated CD8 T lymphocytes during primary immune responses, suggesting a prominent regulatory role. Indeed, production of the proinflammatory cytokine IFN-gamma, but not TNF-alpha, by CD8 T cells was inhibited by CD152 engagement. The inhibition was regulated independent of proliferation and IL-2 production, but dependent on the quality of the TCR signaling. We show that signals induced by CD152 on activated CD8 T lymphocytes reduce the frequency of IFN-gamma(high)-expressing cells. Our data also show that in activated CD8 T cells, the CD152-mediated inhibition of cytokine production is more pronounced than inhibition of their proliferation.     

Helicobacter pylori-secreted factors inhibit dendritic cell IL-12 secretion: a mechanism of ineffective host defense

Helicobacter pylori evades host immune defenses and causes chronic gastritis. Immunity against intestinal pathogens is largely mediated by dendritic cells, yet the role of dendritic cells in acute H. pylori infection is largely unknown. We observed the recruitment of dendritic cells to the gastric mucosa of H. pylori-infected mice. Bone marrow-derived dendritic cells from mice responded to live H. pylori by upregulating the expression of proinflammatory cytokine mRNA (i.e., IL-1alpha, IL-1beta, and IL-6). The supernatant from dendritic cells stimulated with H. pylori for 18 h contained twofold higher levels of IL-12p70 than IL-10 and induced the proliferation of syngeneic splenocytes and type 1 T helper cell cytokine release (IFN-gamma and TNF-alpha). These responses were significantly lower compared with those induced by Acinetobacter lwoffi, another gastritis-causing pathogen more susceptible to host defenses. Analysis of whole H. pylori sonicate revealed the presence of a heat-stable factor secreted from H. pylori that specifically inhibited IL-12 but not IL-10 release from dendritic cells activated by A. lwoffi. Our findings suggest that dendritic cells participate in the host immune response against H. pylori and that their suppression by H. pylori may explain why infected hosts fail to prevent bacterial colonization.     

IL-18 promotes type 1 cytokine production from NK cells and T cells in human intracellular infection

We investigated the role of IL-18 in leprosy, a disease characterized by polar cytokine responses that correlate with clinical disease. In vivo, IL-18 mRNA expression was higher in lesions from resistant tuberculoid as compared with susceptible lepromatous patients, and, in vitro, monocytes produced IL-18 in response to Mycobacterium leprae. rIL-18 augmented M. leprae-induced IFN-gamma in tuberculoid patients, but not lepromatous patients, while IL-4 production was not induced by IL-18. Anti-IL-12 partially inhibited M. leprae-induced release of IFN-gamma in the presence of IL-18, suggesting a combined effect of IL-12 and IL-18 in promoting M. leprae-specific type 1 responses. IL-18 enhanced M. leprae-induced IFN-gamma production rapidly (24 h) by NK cells and in a more sustained manner (5 days) by T cells. Finally, IL-18 directly induced IFN-gamma production from mycobacteria-reactive T cell clones. These results suggest that IL-18 induces type 1 cytokine responses in the host defense against intracellular infection.     

Age-dependent cellular immune responses to Plasmodium vivax Duffy binding protein in humans

The Plasmodium vivax merozoite Duffy binding protein (DBP) contains a cysteine-rich region II (DBPII) that binds to the Duffy Ag receptor for chemokines on erythrocytes, which is essential for parasite invasion. Cellular immune responses to DBPII have not been reported in P. vivax endemic populations, although they may contribute to partial acquired immunity. To examine host cellular immunity to DBPII and identify major T cell epitopes, PBMCs from 107 individuals (2-68 years old) were examined for cytokine production by ELISPOT and/or ELISA to rDBP and overlapping peptides (displaced by 2 aa spanning a 170-aa region of DBPII corresponding to the critical binding motif to the Duffy Ag receptor for chemokines). In P. vivax-exposed subjects, 60 and 71% generated significant rDBP-induced IFN-gamma and IL-10 production, respectively, 11% stimulated IL-2, and IL-5 and IL-13 were not detected. Children <5 years of age had reduced levels and frequency of rDBP-induced IL-10 and IFN-gamma production compared with partially immune older children and adults (p < 0.01). Five major T cell epitopes were identified. Three of these T cell epitopes contained polymorphic residues present in the population. Peptides synthesized corresponding to these variants induced IFN-gamma and IL-10 production to one variant and little response to the other variant in the same individual. These results demonstrate age-dependent and variant-specific cellular immune responses to DBPII and implicate this molecule in partial acquired immunity to P. vivax in endemic populations.     

Intraperitoneal immune cell responses to Eubacterium saphenum in mice

Oral asaccharolytic Eubacterium saphenum, which are newly isolated gram-positive rods and one of the predominant microorganisms in human periodontal pockets, were injected intraperitoneally in mice to elucidate their pathogenicity in periodontal diseases. Infiltrating immune cells in the peritoneal exudate were quantitated and intracellular T cell (CD4+/CD8+/gammadelta+) production of cytokines IL-4 and IFN-gamma which are related to cellular and humoral immunity, respectively, was determined. Neutrophils appeared first in peritoneal exudates, followed by macrophages and lymphocytes, after the injection of either E. saphenum or Porphyromonas gingivalis. Intracellular IL-4+ and IFN-gamma+ gammadelta T cells were detected in the exudates after the injection of E. saphenum (4.6 +/- 0.8% and 10.1 +/- 1.4%, respectively) and P. gingivalis (5.3 +/- 1.6% and 10.1 +/- 2.1%, respectively). The intracellular production of IL-4/IFN-gamma in CD4+/CD8+ T cells was rather low indicating that the main response was from gammadelta T cells which initiated the immune reactions in mouse peritoneal cavities after injection of E. saphenum or P. gingivalis. Serum IgG and IgM levels were elevated in animals injected with E. saphenum and similarly with P. gingivalis. The present study showed that with slight differences, similar modes of cell response and cytokine and Ig production were observed after intraperitoneal injection of both E. saphenum and P. gingivalis, indicating that E. saphenum may play just as important a role in periodontal diseases as P. gingivalis.     

Regulation of T cell cytokine production by dendritic cells

Previous work has established that the dendritic cells (DC) of mouse spleen regulate the IL-2 production, and hence the extent of proliferation, of the CD8 T cells they activate. It is now reported here that interaction of primary CD8 T cells with splenic CD8alpha- DC induced much higher production of IL-3, IFN-gamma and granulocyte-macrophage colony-stimulating factor (GM-CSF), as well as IL-2, than did interaction with CD8alpha+ splenic DC. Furthermore, the CD8alpha- DC also induced higher levels of IL-2, IL-3 and IL-10 production in primary CD4 T cells, compared with that induced by CD8alpha+ DC. These quantitative differences did not involve qualitative shifts in the type of cytokine produced. Interleukin-4 production remained low in all the primary T cell cultures and restimulation experiments in secondary cultures did not reveal any bias in the cytokine production profile. When exogenous IL-2 was added to the primary cultures to ensure equal proliferation in response to CD8alpha- or CD8alpha+ DC, the higher level of production of IL-3, IFN-gamma and GM-CSF induced by CD8alpha- DC was maintained. Thus, this general control of T cell cytokine production by splenic DC involves factors additional to those that govern activation of T cells into cell cycle.     

IL-18 is correlated with type-2 immune response in children with steroid sensitive nephrotic syndrome

Children with steroid sensitive nephrotic syndrome (SSNS) is thought to have dysregulated type-1/type-2 cytokine network. Interleukin (IL)-18 is a cytokine, which may enhance both type-1 and type-2 responses, depending on the cytokines milieu. This prospective study aimed to assess type-1/type-2 cytokine synthesis and production profile in different stages of SSNS and define the potent involvement of IL-18. Twenty-three children with SSNS, aged 2.5-14 years, were studied; 23/23 both in active stage before treatment initiation and in remission still on steroids; 15/23 in remission off steroids as well. Data were compared with those obtained from 25 age-matched controls. The following parameters were assessed: Basic T cell populations, percentages of CD3+/CD69+/IFN-gamma+ and CD3+/CD69+/IL-4+ T cells as well as serum levels of IFN-gamma, IL-2, IL-4, IL-13 and IL-18. No difference in IL-2 levels was found between nephrotic children of all disease stages and controls (p>0.05). Percentage of CD3+/CD69+/IL-4+ T cells and serum levels of IL-4, IL-13 and IL-18 were significantly higher in the active stage of SSNS compared with the remission stages and controls (p<0.05). On the contrary, percentage of CD3+/CD69+/IFN-gamma+ T cells as well as serum IFN-gamma were significantly lower during active disease stage compared with remission stages and controls (p<0.05). In children with SSNS, of all disease stages, serum levels of IL-18 were significantly correlated with both IL-4 and IL-13 (r=0.628 and p<0.0001, r=0.71 and p<0.0001, respectively). It seems that a type-2 cytokine synthesis and production pattern prevails in children with active SSNS and IL-18 expression is significantly correlated with this type-2 immune response.     

Immunosuppressive effect of leukotriene B(4) receptor antagonist in vitro.

Leukotriene B(4) (LTB(4)), which is an arachidonic acid metabolite produced by the 5-lipoxygenase pathway and a well-characterized chemical mediator of inflammation, has been proposed to be an immune response modulator. Here we showed the constitutive expression of the LTB(4) receptor (LTB(4)R) in resting and activated T cells. We found that the LTB(4)R antagonist inhibited T cell proliferation induced by Con A, immobilized anti-CD3 mAb, or IL-2. This inhibitory effect was abolished by addition of LTB(4)R agonist. The LTB(4)R antagonist inhibited IL-2, IFN-gamma, and IL-4 production by anti-CD3-stimulated T cells and also inhibited IL-12-induced IFN-gamma production. Moreover, the LTB(4)R antagonist exerted an additive inhibitory effect to FK506 on T cell proliferation. These results suggest that LTB(4) is intrinsically involved in T cell activation to upregulate cytokine production and proliferation, and thus the LTB(4)R antagonist might be useful as an immunosuppressive agent.     

In vivo immunomodulation following intradermal injection with DNA encoding IL-18.

IL-18, a recently identified cytokine synthesized by different cell types, including Kupffer cells, activated macrophages, and keratinocytes, induces IFN-gamma production by T cells and NK cells. The cDNA encoding IL-18 with its natural signal peptide was cloned under control of the CMV promoter and injected into the skin of mice. A single intradermal injection of this construction led to efficient in vivo expression of IL-18 in cutaneous dermal cells and induced IFN-gamma mRNA production, indicating that it was produced in a biologically active form. In addition, a massive cellular infiltrate was observed in the skin 2 days after injection. When the mice were subsequently infected with Mycobacterium bovis bacillus Calmette-Guérin (BCG), they produced lower levels of anti-BCG Abs than control animals. However, in contrast to their lowered humoral immune response, the mice produced higher amounts of Ag-specific IFN-gamma after in vitro restimulation, as compared with the controls. Therefore, injection of DNA encoding IL-18 into the skin modulates both Ag-specific humoral and T cell responses upon mycobacterial infection. It increases the Th1 type response, which may be particularly useful for the development of new immunotherapeutic or immunoprotective approaches against infections by intracellular parasites, such as mycobacteria.     

Trichuris muris: host intestinal epithelial cell hyperproliferation during chronic infection is regulated by interferon-gamma.

Chronic infection with the intestinal nematode Trichuris muris is associated with an inappropriate type 1 cytokine response (production of predominantly IFN-gamma), whereas resistance to infection requires the induction of a protective type 2 response with the production of interleukin (IL)-4, IL-5, IL-9, and IL-13. T. muris inhabits an intracellular niche within murine intestinal epithelial cells of the caecum and in common with other intestinal helminth infections is associated with gross morphological changes in gut architecture. The purpose of this study was to characterise cytokine production during chronic infection in AKR and severe-combined-immunodeficient (SCID) mice and investigate what effect the anti-parasite response had on epithelial cell proliferation and so regulation of intestinal pathology. Pulse labeling with tritiated thymidine is employed to generate a sensitive cell position-linked proliferation index of the intestinal epithelium at various times postinfection. Infection in AKR mice is characterized by a marked elevation in antigen specific IFN-gamma production from restimulated mesenteric lymph node cells and a significant increase in proliferation of pluripotent epithelial stem cells and transit cells within the crypts. Similarly, elevated IFN-gamma production was observed in the mesenteric lymph nodes and intestinal mucosa of infected SCID mice, with epithelial cell hyperproliferation and the development of crypt hyperplasia in the caecum. Critically, in vivo depletion of IFN-gamma during infection in SCID mice resulted in no significant increase in epithelial cell proliferation and effectively precluded the development of crypt hyperplasia without altering infection outcome. Taken together, the data provides the first detailed cell position linked analysis of epithelial dysregulation during chronic T. muris infection and identifies a critical role for IFN-gamma, either directly or indirectly, in regulation of epithelial cell proliferation during the chronic intestinal inflammation associated with infection.     

CD40-CD40 ligand interaction is central to cell-mediated immunity against Toxoplasma gondii: patients with hyper IgM syndrome have a defective type 1 immune response that can be restored by soluble CD40 ligand trimer.

Cell-mediated immunity that results in IL-12/IFN-gamma production is essential to control infections by intracellular organisms. Studies in animal models revealed contrasting results in regard to the importance of CD40-CD40 ligand (CD40L) signaling for induction of a type 1 cytokine response against these pathogens. We demonstrate that CD40-CD40L interaction in humans is critical for generation of the IL-12/IFN-gamma immune response against Toxoplasma gondii. Infection of monocytes with T. gondii resulted in up-regulation of CD40. CD40-CD40L signaling was required for optimal T cell production of IFN-gamma in response to T. gondii. Moreover, patients with hyper IgM (HIGM) syndrome exhibited a defect in IFN-gamma secretion in response to the parasite and evidence compatible with impaired in vivo T cell priming after T. gondii infection. Not only was IL-12 production in response to T. gondii dependent on CD40-CD40L signaling, but also, patients with HIGM syndrome exhibited deficient in vitro secretion of this cytokine in response to the parasite. Finally, in vitro incubation with agonistic soluble CD40L trimer enhanced T. gondii-triggered production of IFN-gamma and, through induction of IL-12 secretion, corrected the defect in IFN-gamma production observed in HIGM patients. Our results are likely to explain the susceptibility of patients with HIGM syndrome to infections by opportunistic pathogens.