Abhay R. Satoskar

Development of chronic colitis is dependent on the cytokine MIF

The cytokine macrophage-migration inhibitory factor (MIF) is secreted by a number of cell types upon induction by lipopolysaccharide (LPS). Because colitis is dependent on interplay between the mucosal immune system and intestinal bacteria, we investigated the role of MIF in experimental colitis. MIF-deficient mice failed to develop disease, but reconstitution of MIF-deficient mice with wild-type innate immune cells restored colitis. In addition, established colitis could be treated with anti-MIF immunoglobulins. Thus, murine colitis is dependent on continuous MIF production by the innate immune system. Because we found increased plasma MIF concentrations in patients with Crohns disease, these data suggested that MIF is a new target for intervention in Crohns disease.

SAP controls T cell responses to virus and terminal differentiation of TH2 cells.

SH2D1A, which encodes signaling lymphocyte activation molecule (SLAM)–associated protein (SAP), is altered in patients with X-linked lymphoproliferative disease (XLP), a primary immunodeficiency. SAP-deficient mice infected with lymphocytic choriomeningitis virus had greatly increased numbers of CD8+ and CD4+ interferon-γ–producing spleen and liver cells compared to wild-type mice. The immune responses of SAP-deficient mice to infection with Leishmania major together with in vitro studies showed that activated SAP-deficient T cells had an impaired ability to differentiate into T helper 2 cells. The aberrant immune responses in SAP-deficient mice show that SAP controls several distinct key T cell signal transduction pathways, which explains in part the complexity of the XLP phenotypes.

Lacto-N-fucopentaose III found on Schistosoma mansoni egg antigens functions as adjuvant for proteins by inducing Th2-type response.

We have recently demonstrated that induction of Th2 responses by Schistosoma mansoni egg Ag is largely due to carbohydrates on the Ag functioning as adjuvants. Lacto-N-fucopentaose III (LNFPIII), a polylactosamine sugar, is the predominant carbohydrate found in S. mansoni egg Ag. Therefore, using neoglycoprotein, we investigated whether LNFPIII induces in vivo Th2 response and functions as an adjuvant. Following intranasal immunization with LNFPIII linked to human serum albumin (HSA) (HSA-LNFPIII), BALB/c mice mounted a strong Th2 response and produced significantly higher levels of total IgE as well as HSA-specific IgG, IgG1, and IgE. HSA-LNFPIII was over 1000-fold more potent in inducing Ab production as compared with HSA alone. Although LNFPIII itself did not function as an epitope for either IgG or IgE, its conjugation with protein was essential for the adjuvant activity. Moreover, fucose residue on LNFPIII was crucial for induction of Ab production. Nasal lymphocytes from mice immunized with HSA-LNFPIII produced IL-4, IL-5, and IL-10, but not IFN-γ following in vitro stimulation with HSA or HSA-LNFPIII. In addition, these activated nasal lymphocytes also showed a significant increase of B7-2 expression on B220-positive cells. Furthermore, not only intranasal but also both i.p. and s.c. immunization with HSA-LNFPIII induced significant production of HSA-specific Abs compared with the immunization with HSA alone, suggesting that the activity of LNFPIII was not restricted on particular route of immunization. These results demonstrate that Lewis type carbohydrate LNFPIII can function as an adjuvant by their ability to induce a Th2 response.

Cutting Edge: Selective IL-18 Requirements for Induction of Compartmental IFN-γ Responses During Viral Infection

Optimal protective effects for defense against infection require orchestration of immune responses spanning multiple host compartments and divergent local regulation at particular sites. During murine cytomegalovirus infections known to target spleen and liver, IL-12-induced IFN-γ from NK cells is crucial for resistance. However, the roles for IL-18 and/or IL-12 in regulating hepatic IFN-γ responses, as compared with systemic or splenic responses, have not been defined. In this report, mice genetically deficient in either IL-18 or IL-12p35 exhibited up to 95% reductions in systemic and splenic IFN-γ responses. Surprisingly, IFN-γ responses were preserved in the livers of IL-18-deficient, but not IL-12p35-deficient, mice. Cytokine requirements for host survival also differed. Under conditions where mice lacking IL-12p35 exhibited 100% mortality, those lacking IL-18 survived. Taken together, our results delineate contrasting compartmental requirements for IL-18 and suggest that preservation of local, hepatic IFN-γ production is critical for host defense during murine cytomegalovirus challenge.

The Cell Surface Receptor SLAM Controls T Cell and Macrophage Functions

Signaling lymphocyte activation molecule (SLAM), a glycoprotein expressed on activated lymphocytes and antigen-presenting cells, has been shown to be a coregulator of antigen-driven T cell responses and is one of the two receptors for measles virus. Here we show that T cell receptor–induced interleukin (IL)-4 secretion by SLAM−/− CD4+ cells is down-regulated, whereas interferon γ production by CD4+ T cells is only slightly up-regulated. Although SLAM controls production of IL-12, tumor necrosis factor, and nitric oxide in response to lipopolysaccharide (LPS) by macrophages, SLAM does not regulate phagocytosis and responses to peptidoglycan or CpG. Thus, SLAM acts as a coreceptor that regulates signals transduced by the major LPS receptor Toll-like receptor 4 on the surface of mouse macrophages. A defective macrophage function resulted in an inability of SLAM−/− C57Bl/6 mice to remove the parasite Leishmania major. We conclude that the coreceptor SLAM plays a central role at the interface of acquired and innate immune responses.

Macrophage Migration Inhibitory Factor Deficiency Impairs Atherosclerosis in Low-Density Lipoprotein Receptor-Deficient Mice

Background— Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine expressed widely by vascular cells. However, scant in vivo evidence supports direct participation of MIF in atherogenesis. Therefore, we investigated whether deficiency of MIF modulates atherosclerotic lesion formation and composition in low-density lipoprotein receptor–deficient (LDLr−/−) mice. Methods and Results— MIF−/−LDLr−/− and LDLr−/− mice were generated and consumed an atherogenic diet for 12 or 26 weeks. MIF−/−LDLr−/− mice had significantly reduced abdominal aorta lipid deposition and intimal thickening from aortic arch throughout the abdominal aorta compared with LDLr−/− mice. Marked retardation of atherosclerosis over time in MIF-deficient mice accompanied decreased lesion cell proliferation. At 26 weeks, 20% of MIF-deficient mice developed only early, fatty streak–like lesions, whereas >80% of LDLr−/− mice developed advanced lesions containing calcification and lipid cores. Analysis of smooth muscle cells from mouse aortae demonstrated that MIF deficiency reduced smooth muscle cell proliferation, cysteine protease expression, and elastinolytic and collagenolytic activities. Conclusions— Deficiency of MIF reduces atherogenesis in LDLr−/− mice. These results provide novel insight into inflammatory pathways operating in atheromata and identify a new potential target for modulating atherogenesis.

Endogenous IL-4 is necessary for effective drug therapy against visceral leishmaniasis.

It is well established that a fully competent immune response is required for the successful drug treatment of visceral leishmaniasis. However, recent studies have cast some doubt as to which elements of the immune response synergize with chemotherapeutic treatment. The role of the Th2 response and IL‐4 in particular during visceral leishmaniasis awaits clarification. We, therefore, examined the effectiveness of sodium stibogluconate treatment on Leishmania donovani infection in BALB/c wild‐type and IL‐4–/– mice. Parasite burdens in L. donovani‐infected IL‐4+/+ and IL‐4–/–, as we have previously shown for B6/129 mice, were similar, despite an apparent type 1 antibody response in infected IL‐4–/– mice, demonstrated by increased levels of parasite‐specific IgG2a and decreased IgG1. Unexpectedly IL‐4–/– mice responded poorly to sodium stibogluconate treatment with increased parasite burdens in all tissues examined. Furthermore, drug therapy of IL‐4–/– but not IL‐4+/+ mice resulted in significant reductions in splenocyte IFN‐γ mRNA transcripts and in serum IFN‐γ levels. These results demonstrate that IL‐4 has an important role in effective anti‐leishmanial chemotherapy which seems to be related to modulation of IFN‐γ production.

ENHANCED TH2-LIKE RESPONSES IN IL-1 TYPE 1 RECEPTOR-DEFICIENT MICE

IL‐1 has a number of effects on T cell growth but a specific role for IL‐1 in T cell responses in vivo has not been elucidated. In this study the role of IL‐1 in Th1/Th2 responses was examined in mice deficient for the IL‐1 type 1 receptor (IL‐1RI −/−) during cutaneous Leishmania major infection or following immunization with keyhole limpet hemocyanin (KLH). After inoculation of L. major stationary phase promastigotes into the hind footpad, both IL‐1RI−/− and wild‐type (WT) mice developed small lesions which resolved spontaneously. Lymphnode cells from infected IL‐1RI−/− mice produced significantly more IL‐4 and IL‐10 than those from WT mice following antigenic stimulation in vitro. Splenocytes from IL‐1RI−/− and WT mice showed similar levels of antigen‐induced proliferation. In contrast, splenocyte cultures from the IL‐1RI−/− mice contained significantly more IL‐4 than those from WT mice. Similar results were also obtained after immunization with KLH. While lymph node cells from both IL‐1RI−/− and WT mice displayed similar levels of KLH‐specific proliferation, those from IL‐1RI −/− mice produced significantly more IL‐4 than those from WT mice. Conversely, antigen‐stimulated lymph node cells from WT mice secreted significantly greater amounts of IFN‐γ as compared with those from IL‐1RI −/− mice. These data indicate that while IL‐1 is not required for mounting an immune response or antigen‐dependent proliferation, it appears to be required for normal regulation of Th1/Th2 responses and may function to negatively regulate IL‐4 expression.

Genetically Resistant Mice Lacking IL-18 Gene Develop Th1 Response and Control Cutaneous Leishmania major Infection

IL-18 has been shown to play a critical role in the development of a Th1 response and immunity against intracellular pathogens. To determine the role of IL-18 in the development of protective immunity against Leishmania major, we have analyzed the course of cutaneous L. major in IL-18-deficient C57BL/6 mice (IL-18−/−) compared with similarly infected wild-type mice (IL-18+/+). After L. major infection, IL-18−/− mice may develop larger lesions during early phase of infection but eventually will resolve them as efficiently as IL-18+/+ mice. By 2 wk after infection, although Ag-stimulated lymph node cells from L. major-infected IL-18+/+ and IL-18−/− mice produced similar levels of IFN-γ, those from IL-18−/− mice produced significantly more IL-12 and IL-4. By 10 wk after infection, both IL-18+/+ and IL-18−/− mice had resolved L. major infection. At this time, lymph node cells from both IL-18+/+ and IL-18−/− mice produced IL-12 and IFN-γ but no IL-4. Furthermore, administration of anti-IFN-γ Abs to IL-18−/− mice rendered them susceptible to L. major. These results indicate that despite the role IL-18 may play in early control of cutaneous L. major lesion growth, this cytokine is not critical for development of protective Th1 response and resolution of L. major infection.

Cutting Edge: Susceptibility to the Larval Stage of the Helminth Parasite Taenia crassiceps Is Mediated by Th2 Response Induced Via STAT6 Signaling

Using STAT6−/− BALB/c mice, we analyzed the role of STAT6-induced Th2 response in determining the outcome of murine cysticercosis caused by the helminth parasite Taenia crassiceps. After T. crassiceps infection, wild-type BALB/c mice developed a strong Th2-like response; produced high levels of IgG1, IgE, IL-4, as well as IL-13; and remained susceptible to T. crassiceps. In contrast, similarly infected STAT6−/− mice mounted a strong Th1-like response; produced high levels of IgG2a, IL-12, IFN-γ, as well as nitric oxide; and efficiently controlled T. crassiceps infection. These findings demonstrate that Th2-like response induced via STAT6-mediated signaling pathway mediates susceptibility to T. crassiceps and, furthermore, that unlike the case in most helminths, immunity against T. crassiceps is mediated by a Th1-like rather than Th2-like response.