The antigen dose determines T helper subset development by regulation of CD40 ligand

Although the amount of antigen and the strength of T cell stimulation have been suggested to regulate Th1 vs. Th2 polarization, it remains unclear how the antigen dose and the strength of signal is detected by the T cell and translated into differential cytokine production. Using co-cultures of dendritic cells (DC) and ovalbumin (OVA)-specific CD4+ T cells obtained from RAG-2)(-/-) DO11.10 mice, we show here that high-dose antigen induced Th1 development by up-regulation of CD40 ligand (CD40L), whereas low-dose antigen stimulation failed to induce CD40L and promoted Th2 development. CD40-CD40L interaction was essential for IL-12 production by DC. In the absence, de novo IL-4 production by T cells and autocrine Th2 development was induced. Furthermore, our results demonstrate that LFA-1/ ICAM interaction promotes Th1 differentiation by lowering the antigen dose required for CD40L up-regulation. Thus, we propose that (1) peptide-MHC density and (2) accessory molecules such as LFA-1 determine T helper polarization by regulation of CD40L.

Hapten-induced colitis associated with maintained Th1 and inflammatory responses in IFN-gamma receptor-deficient mice

IFN-gamma is a potent pro-inflammatory cytokine thought to be involved in the pathogenesis of Crohn's disease. To further define the role of IFN-gamma in intestinal inflammation, we studied the effects of intra-colonic 2,4,6-trinitrobenzene sulfonic acid (TNBS) instillation in mice with a functionally inactivated IFN-gamma receptor 1 (IFN-gammaR1(- / -)). Our results indicate that IFN-gamma is not necessary for the induction of hapten-induced colitis: after TNBS administration both wild-type and IFN-gammaR1(- / -) mice lost body weight, and the histological features of TNBS-induced colitis were comparable. Colons of IFN-gammaR1(- / -) mice contained a greater number of cells, represented by macrophages and CD4(+) T cells; caudal lymph node cells produced more IFN-gamma and TNF-alpha upon stimulation in vitro. Moreover, IL-18 and IL-12 p40 RNA levels were comparably up-regulated after TNBS treatment in IFN-gammaR1(- / -) wild-type mice. These findings demonstrate that IFN-gamma is dispensable for the development of TNBS-induced colitis. Importantly, the production of Th1 cytokines (e. g. IFN-gamma and TNF-alpha) by caudal lymph node T lymphocytes was enhanced rather than decreased in IFNgammaR1(- / -) mice with no evidence for default Th2 development.

Hapten-induced colitis associated with maintained Th1 and inflammatory responses in IFN-gamma receptor-deficient mice

IFN-gamma is a potent pro-inflammatory cytokine thought to be involved in the pathogenesis of Crohn's disease. To further define the role of IFN-gamma in intestinal inflammation, we studied the effects of intra-colonic 2,4,6-trinitrobenzene sulfonic acid (TNBS) instillation in mice with a functionally inactivated IFN-gamma receptor 1 (IFN-gammaR1(- / -)). Our results indicate that IFN-gamma is not necessary for the induction of hapten-induced colitis: after TNBS administration both wild-type and IFN-gammaR1(- / -) mice lost body weight, and the histological features of TNBS-induced colitis were comparable. Colons of IFN-gammaR1(- / -) mice contained a greater number of cells, represented by macrophages and CD4(+) T cells; caudal lymph node cells produced more IFN-gamma and TNF-alpha upon stimulation in vitro. Moreover, IL-18 and IL-12 p40 RNA levels were comparably up-regulated after TNBS treatment in IFN-gammaR1(- / -) wild-type mice. These findings demonstrate that IFN-gamma is dispensable for the development of TNBS-induced colitis. Importantly, the production of Th1 cytokines (e. g. IFN-gamma and TNF-alpha) by caudal lymph node T lymphocytes was enhanced rather than decreased in IFNgammaR1(- / -) mice with no evidence for default Th2 development.

IL-4 and IL-10 antagonize IL-12-mediated protection against acute vaccinia virus infection with a limited role of IFN-gamma and nitric oxide synthetase 2

Resistance or susceptibility to most infectious diseases is strongly determined by the balance of type 1 vs type 2 cytokines produced during infection. However, for viruses, this scheme may be applicable only to infections with some cytopathic viruses, where IFN-gamma is considered as mandatory for host defense with little if any participation of type 2 responses. We studied the role of signature Th1 (IL-12, IFN-gamma) and Th2 (IL-4, IL-10) cytokines for immune responses against vaccinia virus (VV). IL-12-/- mice were far more susceptible than IFN-gamma-/- mice, and primary CTL responses against VV were absent in IL-12-/- mice but remained intact in IFN-gamma-/- mice. Both CD4+ and CD8+ T cells from IL-12-/- mice were unimpaired in IFN-gamma production, although CD4+ T cells showed elevated Th2 cytokine responses. Virus replication was impaired in IL-4-/- mice and, even more strikingly, in IL-10-/- mice, which both produced elevated levels of the proinflammatory cytokines IL-1alpha and IL-6. Thus, IL-4 produced by Th2 cells and IL-10 produced by Th2 cells and probably also by macrophages counteract efficient anti-viral host defense. Surprisingly, NO production, which is considered as a major type 1 effector pathway inhibited by type 2 cytokines, appears to play a limited role against VV, because NO sythetase 2-deficient mice did not show increased viral replication. Thus, our results identify a new role for IL-12 in defense beyond the induction of IFN-gamma and show that IL-4 and IL-10 modulate host protective responses to VV.

Antifungal type 1 responses are upregulated in IL-10-deficient mice

C57BL/6 mice are highly resistant to infections caused by Candida albicans and Aspergillus fumigatus. To elucidate the role of IL-10 produced by C57BL/6 mice during these infections, parameters of infection and immunity to it were evaluated in IL-10-deficient and wild-type mice with disseminated or gastrointestinal candidiasis or invasive pulmonary aspergillosis. Unlike parasitic protozoan infection, C. albicans or A. fumigatus infection did not induce significant acute toxicity in IL-10-deficient mice, who, instead, showed reduced fungal burden and fungal-associated inflammatory responses. The increased resistance to infections as compared to wild-type mice was associated with upregulation of innate and acquired antifungal Th1 responses, such as a dramatically higher production of IL-12, nitric oxide (NO) and TNF-alpha as well as IFN-gamma by CD4+ T cells. Pharmacological inhibition of NO production greatly reduced resistance to gastrointestinal candidiasis, thus pointing to the importance of IL-10-dependent NO regulation at mucosal sites in fungal infections. These results are reminiscent of those obtained in genetically susceptible mice, in which IL-10 administration increased, and IL-10 neutralization decreased, susceptibility to C. albicans and A. fumigatus infections. Collectively, these observations indicate that the absence of IL-10 augments innate and acquired antifungal immunity by upregulating type 1 cytokine responses. The resulting protective Th1 responses lead to a prompt reduction of fungal growth, thus preventing tissue destruction and lethal levels of proinflammatory cytokines.

OX40-deficient mice are defective in Th cell proliferation but are competent in generating B cell and CTL Responses after virus infection

OX40, a member of the TNF receptor superfamily, is expressed on activated T cells and implicated in stimulation of T cells and T-dependent humoral responses. We generated OX40-/- mice and found that the formation of extrafollicular plasma cells, germinal centers, and antibody responses was independent of OX40. After infection with LCMV and influenza virus, OX40-/- mice retain primary and memory cytotoxic T cell responses with normal expansion and decline of specific CTL. In contrast, CD4+ T cell proliferation and the number of IFN-gamma-producing CD4+ T cells were reduced in OX40-/- mice. Moreover, the number of CD4+ T cells infiltrating the lungs of influenza virus-infected OX40-/- mice was reduced. These results define a unique role of OX40 in the generation of optimal CD4+ T cell responses in vivo.

Interleukin-4 causes susceptibility to invasive pulmonary aspergillosis through suppression of protective type I responses

Aspergillus fumigatus, an opportunistic fungal pathogen, causes multiple allergic and nonallergic airway diseases. Invasive pulmonary aspergillosis (IPA) is a nonallergic, life-threatening disease of immunocompromised patients. In a murine model of IPA, interleukin (IL)-4-deficient (IL-4-/-) BALB/c mice were used to examine the role of IL-4 in lung pathology and immune responses. IL-4-/- mice were more resistant than wild-type mice to infection caused by multiple intranasal injections of viable A. fumigatus conidia. Resistance was associated with decreased lung inflammatory pathology, impaired T helper (Th)-2 responses (including lung eosinophilia), and an IL-12-dependent Th1 response. In contrast, development of host-detrimental antifungal Th2 cells occurred in IL-12-/- and interferon-gamma-/- mice and in IL-4-/- mice when subjected to IL-12 neutralization. These results demonstrate that IL-4 renders mice susceptible to infection with A. fumigatus by inhibition of protective Th1 responses. IL-4 appears to have a distinct role in the pathogenesis of allergic and nonallergic lung diseases caused by the fungus.

CD2 sets quantitative thresholds in T cell activation

It has been proposed that CD2, which is highly expressed on T cells, serves to enhance T cell-antigen presenting cell (APC) adhesion and costimulate T cell activation. Here we analyzed the role of CD2 using CD2-deficient mice crossed with transgenic mice expressing a T cell receptor specific for lymphocytic choriomeningitis virus (LCMV)-derived peptide p33. We found that absence of CD2 on T cells shifted the p33-specific dose-response curve in vitro by a factor of 3-10. In comparison, stimulation of T cells in the absence of lymphocyte function-associated antigen (LFA)-1-intercellular adhesion molecule (ICAM)-1 interaction shifted the dose-response curve by a factor of 10, whereas absence of both CD2-CD48 and LFA-1-ICAM-1 interactions shifted the response by a factor of approximately 100. This indicates that CD2 and LFA-1 facilitate T cell activation additively. T cell activation at low antigen density was blocked at its very first steps, as T cell APC conjugate formation, TCR triggering, and Ca(2+) fluxes were affected by the absence of CD2. In vivo, LCMV-specific, CD2-deficient T cells proliferated normally upon infection with live virus but responded in a reduced fashion upon cross-priming. Thus, CD2 sets quantitative thresholds and fine-tunes T cell activation both in vitro and in vivo.

Outcome of Staphylococcus aureus-triggered sepsis and arthritis in IL-4-deficient mice depends on the genetic background of the host

Disruption of the IL-4 gene in two inbred mouse strains revealed a dual role of IL-4 in Staphylococcus aureus sepsis and arthritis depending on the host's genetic background. IL-4 was protective in 129SV mice, since 5 days after S. aureus inoculation IL-4(-/-) mice displayed 70% mortality as compared to survival of all 129SV wild-type counterparts. On the other hand, IL-4 was detrimental in C57BL/6 mice, since survival of IL-4(-/-) C57BL/6 mice was increased, as compared to wild-type controls, due to decreased staphylococcal growth. Altogether, our results show the dual role of IL-4 in S. aureus sepsis and arthritis, depending on the genetic background of the host.

Cutting edge: lymphoproliferative disease in the absence of CTLA-4 is not T cell autonomous

Mice deficient for the expression of CTLA-4 develop a lethal lymphoproliferative syndrome and multiorgan inflammation leading to death at about 4 wk of age. Here we show that RAG2-deficient mice reconstituted with CTLA-4-deficient bone marrow do not develop a lymphoproliferative syndrome despite lymphocyte infiltration mainly into pericardium and liver. Moreover, RAG2-deficient mice reconstituted with a mixture of normal and CTLA-4-deficient bone marrow remain healthy and do not develop any disease. Thus, the lethal disease observed in CTLA-4-deficient mice is not T cell autonomous and can be prevented by factors produced by normal T cells.

CD8(+) T cells mediate CD40-independent maturation of dendritic cells in vivo

Induction of cytotoxic T lymphocyte (CTL) responses against minor histocompatibility antigens is dependent upon the presence of T cell help and requires the interaction of CD40 on dendritic cells (DCs) with CD40 ligand on activated T helper cells (Th). This study demonstrates that CD40 is neither involved in Th-dependent nor Th-independent antiviral CTL responses. Moreover, the data show that DC maturation occurs in vivo after viral infection in the absence of CD40 and Th. This maturation did not require viral infection of DCs but was mediated by peptide-specific CD8(+) T cells. Surprisingly, naive CD8(+) T cells were able to trigger DC maturation within 24 h after activation in vivo and in vitro. Moreover, peptide-activated CD8(+) T cells were able to induce maturation in trans, as DCs that failed to present the relevant antigen in vivo also underwent maturation. Upon isolation, the in vivo-stimulated DCs were able to convert a classically Th-dependent CTL response (anti-HY) into a Th-independent response in vitro. Thus, antiviral CD8(+) T cells are sufficient for the maturation of DCs in the absence of CD40.

The role of B cells in acute and chronic infections

The important role of B cells in protection against secondary viral infections has been recognized for a long time. Recent evidence suggests that B cells are also critically involved in protective immune reactions classically attributed to T cells. Specifically, antibodies have been documented to protect from many primary viral and parasitic infections and to be indispensable for the control of latent viral infections. Current vaccine strategies should take into account this pivotal role of antibodies.

Sensory impairments and delayed regeneration of sensory axons in interleukin-6-deficient mice

Interleukin-6 (IL-6) is a multifunctional cytokine mediating inflammatory or immune reactions. Here we investigated the possible role of IL-6 in the intact or lesioned peripheral nervous system using adult IL-6 gene knockout (IL-6(-/-)) mice. Various sensory functions were tested by applying electrophysiological, morphological, biochemical, and behavioral methods. There was a 60% reduction of the compound action potential of the sensory branch of IL-6(-/-) mice as compared with the motor branch in the intact sciatic nerve. Cross sections of L5 DRG of IL-6(-/-) mice showed a shift in the relative size distribution of the neurons. The temperature sensitivity of IL-6(-/-) mice was also significantly reduced. After crush lesion of the sciatic nerve, its functional recovery was delayed in IL-6(-/-) mice as analyzed from a behavioral footprint assay. Measurements of compound action potentials 20 d after crush lesion showed that there was a very low level of recovery of the sensory but not of the motor branch of IL-6(-/-) mice. Similar results of sensory impairments were obtained with mice showing slow Wallerian degeneration (Wlds) and a delayed lesion-induced recruitment of macrophages. However, in contrast to WldS mice, in IL-6(-/-) mice we observed the characteristic lesion-induced invasion of macrophages and the upregulation of low-affinity neurotrophin receptor p75 (p75LNTR) mRNA levels identical to those of IL-6(+/+) mice. Thus, the mechanisms leading to the common sensory deficiencies were different between IL-6(-/-) and WldS mice. Altogether, the results suggest that interleukin-6 is essential to modulate sensory functions in vivo.

Influenza virus: a novel method to assess viral and neutralizing antibody titers in vitro

The present report describes novel in vitro assays to determine influenza virus titers and virus neutralizing antibody levels. For determination of viral titers, serial dilutions of influenza virus were incubated with MDCK-cells and cultured for 48 h under a methylcellulose overlay in 24 well plates. Cells were fixed, permeabilized and stained with a monoclonal antibody specific for hemagglutitin (HA) and a peroxidase labelled second stage antibody. The sensitivity of the assay was 100-1000 times greater than a conventional hemagglutination test using fresh chicken blood. For determination of influenza virus neutralizing activity, viral samples were incubated with serial dilutions of antibody and residual viral activity was assessed in 96 well plates by the same procedure as described above. This assay made it possible to distinguish between IgM and IgG antibody titers and was about 5-10 fold more sensitive than a classical hemagglutination inhibition assay using fresh chicken blood.

Developmental regulation of Lck targeting to the CD8 coreceptor controls signaling in naive and memory T cells

The question of whether enhanced memory T cell responses are simply due to an increased frequency of specific cells or also to an improved response at the single cell level is widely debated. In this study, we analyzed T cell receptor (TCR) transgenic memory T cells and bona fide memory T cells isolated from virally infected normal mice using the tetramer technology. We found that memory T cells are qualitatively different from naive T cells due to a developmentally regulated rearrangement of the topology of the signaling machinery. In naive cytotoxic T cells, only a few CD8 molecules are associated with Lck and the kinase is homogeneously distributed inside the cell. However, in vivo priming of naive T cells induces the targeting of Lck to the CD8 coreceptor in the cell membrane and the consequent organization of a more efficient TCR signaling machinery in effector and memory cells.

Distinct kinetics of cytokine production and cytolysis in effector and memory T cells after viral infection

In the present study, naive T cells were compared with in vivo generated effector and memory T cells expressing the same TCR specific for lymphocytic choriomeningitis virus. Upon restimulation in vitro, the same minimal concentrations of the full agonist peptide p33 and also of weak and partial agonist peptides were required for proliferation of naive, effector and memory T cells, indicating no difference in threshold of activation. However, activation kinetics were distinct. While effector cytotoxic T cells exhibited immediate ex vivo lytic effector function, naive and memory T cells required 12 h and more exposure to antigen to develop lytic activity. However, both effector and memory T cells contained IFN-gamma mRNA in vivo and required less than 3 h for secretion of cytokines upon restimulation in vitro. In contrast, naive T cells did not contain IFN-gamma mRNA and required more than 12 h for cytokine secretion. Our results show that memory T cells exhibit a unique phenotype in that they produce cytokines and commit to proliferation as rapidly as effector cells, whereas they resemble naive T cells in the time requirement for development of cytolytic function.

Distinct kinetics of cytokine production and cytolysis in effector and memory T cells after viral infection

In the present study, naive T cells were compared with in vivo generated effector and memory T cells expressing the same TCR specific for lymphocytic choriomeningitis virus. Upon restimulation in vitro, the same minimal concentrations of the full agonist peptide p33 and also of weak and partial agonist peptides were required for proliferation of naive, effector and memory T cells, indicating no difference in threshold of activation. However, activation kinetics were distinct. While effector cytotoxic T cells exhibited immediate ex vivo lytic effector function, naive and memory T cells required 12 h and more exposure to antigen to develop lytic activity. However, both effector and memory T cells contained IFN-gamma mRNA in vivo and required less than 3 h for secretion of cytokines upon restimulation in vitro. In contrast, naive T cells did not contain IFN-gamma mRNA and required more than 12 h for cytokine secretion. Our results show that memory T cells exhibit a unique phenotype in that they produce cytokines and commit to proliferation as rapidly as effector cells, whereas they resemble naive T cells in the time requirement for development of cytolytic function.

Interleukin 6 influences germinal center development and antibody production via a contribution of C3 complement component

Mice rendered deficient for interleukin (IL) 6 by gene targeting were evaluated for their response to T cell-dependent antigens. Antigen-specific immunoglobulin (Ig)M levels were unaffected whereas all IgG isotypes showed varying degrees of alteration. Germinal center reactions occurred but remained physically smaller in comparison to those in the wild-type mice. This concurred with the observations that molecules involved in initial signaling events leading to germinal center formation were not altered (e.g., B7.2, CD40 and tumor necrosis factor R1). T cell priming was not impaired nor was a gross imbalance of T helper cell (Th) 1 versus Th2 cytokines observed. However, B7.1 molecules, absent from wild-type counterparts, were detected on germinal center B cells isolated from the deficient mice suggesting a modification of costimulatory signaling. A second alteration involved impaired de novo synthesis of C3 both in serum and germinal center cells from IL-6-deficient mice. Indeed, C3 provided an essential stimulatory signal for wild-type germinal center cells as both monoclonal antibodies that interrupted C3-CD21 interactions and sheep anti-mouse C3 antibodies caused a significant decrease in antigen-specific antibody production. In addition, germinal center cells isolated from C3-deficient mice produced a similar defect in isotype production. Low density cells with dendritic morphology were the local source of IL-6 and not the germinal center lymphocytes. Adding IL-6 in vitro to IL-6-deficient germinal center cells stimulated cell cycle progression and increased levels of antibody production. These findings reveal that the germinal center produces and uses molecules of the innate immune system, evolutionarily pirating them in order to optimally generate high affinity antibody responses.

Differential effects of the absence of interferon-gamma and IL-4 in acute graft-versus-host disease after allogeneic bone marrow transplantation in mice

Graft-versus-host disease (GVHD), in which immunocompetent donor cells attack the host, remains a major cause of morbidity after allogeneic bone marrow transplantation (BMT). To understand the role of cytokines in the pathobiology of GVHD, we used cytokine knockout (KO) mice as a source of donor T cells. Two different MHC-disparate strain combinations were examined: BALB/c (H2(d)) donors into lethally irradiated C57BL/6 (H2(b)) recipients or C57BL/6 (H2(b)) donors into B10.BR (H2(k)) recipients. Donor cells were from mice in which either the interferon-gamma (IFN-gamma) or the IL-4 gene was selectively disrupted to understand the role of these cytokines in acute GVHD. In both strain combinations the same pattern was noted with regard to GVHD onset and morbidity. All mice exhibited the classic signs of acute GVHD: weight loss with skin, gut, and liver pathology resulting in morbidity and mortality. Surprisingly, donor cells obtained from mice lacking IFN-gamma gave rise to accelerated morbidity from GVHD when compared with cells from wild-type control donors. Similar results were obtained using normal donors when neutralizing antibodies to IFN-gamma were administered immediately after the BMT. These results suggest that IFN-gamma plays a role in protection from acute GVHD. In marked contrast, cells obtained from IL-4 KO mice resulted in protection from GVHD compared with control donors. Splenocytes from IFN KO mice stimulated with a mitogen proliferated to a significantly greater extent and produced more IL-2 compared with splenocytes obtained from IL-4 KO or control mice. Additionally, there was increased IL-2 production in the spleens of mice undergoing GVHD using IFN-gamma KO donors. These results therefore indicate, with regard to the TH1/ TH2 cytokine paradigm, the absence of a TH1-type cytokine can be deleterious in acute GVHD, whereas absence of a TH2 cytokine can be protective.

IFN-gamma is required for IL-12 responsiveness in mice with Candida albicans infection

To elucidate the role of IFN-gamma in antifungal CD4+ Th-dependent immunity, 129/Sv/Ev mice deficient for IFN-gamma receptor (IFN-gammaR(-/-)) were assessed for susceptibility to gastrointestinal or systemic Candida albicans infection and for parameters of innate and adaptive T helper immunity. IFN-gammaR(-/-) mice failed to mount protective Th1-mediated acquired immunity upon mucosal immunization or in response to a live vaccine strain of the yeast. The impaired Th1-mediated resistance correlated with defective IL-12 responsiveness, but not IL-12 production, and occurred in the presence of an increased innate antifungal resistance. The development of nonprotective Th2 responses was observed in IFN-gammaR(-/-) mice upon mucosal infection and subsequent reinfection. However, under experimental conditions of Th2 cell activation, the occurrence of Th2 cell responses was similar in IFN-gammaR(-/-) and in IFN-gammaR(+/+) mice. These results indicate the complex immunoregulatory role of IFN-gamma in the induction of mucosal and nonmucosal anticandidal Th cell responses; IFN-gamma is not essential for the occurrence of Th2 responses but is required for development of IL-12-dependent protective Th1-dependent immunity.

Eosinophils are not required to induce airway hyperresponsiveness after nematode infection

Eosinophilic inflammation of the airways is believed to play a central role in the pathogenesis of bronchial asthma. Inoculation of mice with the nematode Nippostrongylus brasiliensis induces pulmonary inflammation, characterized by a marked infiltration of eosinophils, subsequent to the migration of parasites through the lungs. Infection is associated with polarized Th2 responses in different strains of mice tested. Thus, this model may be useful to determine the relationship between established pulmonary eosinophilic inflammation, Th2 immune responses and airway changes in a nonallergic background. In the present study, we have used IL-5-deficient mice to evaluate the role of IL-5 in eosinophilic lung inflammation and airway hyperresponsiveness (AHR). In wild-type C57B/6 mice, infection with N. brasiliensis resulted in eosinophil accumulation, associated with extensive lung damage characterized by hemorrhage and alveolar wall destruction, and a strong AHR following methacholine treatment. In IL-5-deficient mice, eosinophil infiltration and the associated lung damage was abrogated. Nonetheless, AHR was unimpaired. Our results suggest that eosinophil accumulation plays a central role in lung damage but is not responsible for the induction of airway constriction following N. brasiliensis infection.

Interleukin 6 plays a key role in the development of antigen-induced arthritis

To investigate the direct role of interleukin (IL) 6 in the development of rheumatoid arthritis, IL-6-deficient (IL-6 -/-) mice were backcrossed for eight generations into C57BL/6 mice, a strain of mice with a genetic background of susceptibility for antigen-induced arthritis (AIA). Both histological and immunological comparisons were made between IL-6-deficient (IL-6 -/-) mice and wild-type (IL-6 +/+) littermates after the induction of AIA. Although all IL-6 +/+ mice developed severe arthritis, only mild arthritis was observed in IL-6 -/- mice. Safranin O staining demonstrated that articular cartilage was well preserved in IL-6 -/- mice, whereas it was destroyed completely in IL-6 +/+ mice. In addition, comparable mRNA expression for both IL-1beta and tumor necrosis factor alpha, but not for IL-6, was detected in the inflamed joints of IL-6 -/- mice, suggesting that IL-6 may play a more crucial role in cartilage destruction than either IL-1beta or tumor necrosis factor alpha. In immunological comparisons, both antigen-specific in vitro proliferative response in lymph node cells and in vivo antibody production were elicited in IL-6 -/- mice, but they were reduced to less than half of that found in IL-6 +/+ mice. Lymph node cells of IL-6 -/- mice produced many more Th2 cytokines than did IL-6 +/+ mice with either antigen-specific or nonspecific stimulation in in vitro culture. Taken together, these results indicate that IL-6 may play a key role in the development of AIA at the inductive as well as the effector phase, and the blockade of IL-6 is possibly beneficial in the treatment of rheumatoid arthritis.

IL-6-deficient mice resist myelin oligodendrocyte glycoprotein-induced autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is induced by immunization with myelin components including myelin oligodendrocyte glycoprotein (MOG). Myelin-specific Th1 cells enter the central nervous system (CNS) via binding of very late antigen 4 (VLA-4) to the endothelial vascular cell adhesion molecule 1 (VCAM-1). In the present study, mice with a homologous disruption of the gene encoding IL-6 are found to be resistant to MOG-induced EAE as evidenced by absence of clinical symptoms, minimal infiltration of CD3+ T cells and monocytes into the CNS and lack of demyelination. The failure to induce EAE in IL-6-/- mice is not due to the absence of priming, since lymphocytes of immunized IL-6-/- mice proliferate in response to MOG and produce pro-inflammatory cytokines including IL-2 and IFN-gamma. However, in MOG-immunized IL-6-/- mice, serum anti-MOG antibody titers were found to be drastically reduced. This observation is unlikely to be responsible for resistance to EAE, because B cell-deficient (microMT) mice proved to be fully susceptible to the disease. A striking difference between MOG-immunized wild-type (wt) and IL-6-/- mice was the expression of endothelial VCAM-1 and ICAM-1, which were dramatically up-regulated in the CNS in wt but not in IL-6-/- mice. Taking into account recent studies on the role of VCAM-1 in the entry of Th1 cells into the CNS, the absence of VCAM-1 on endothelial cells in IL-6-/- mice may explain their resistance to EAE.

Differences between IL-4R alpha-deficient and IL-4-deficient mice reveal a role for IL-13 in the regulation of Th2 responses

Allergens and infections with parasitic helminths preferentially induced Th2 immune responses associated with elevated levels of serum immunoglobulin E (IgE) and expansion of eosinophils and mast cells. Interleukin-4 (IL-4) is a key cytokine in the differentiation of naive CD4+ T cells into Th2 cells, which produce a panel of cytokines including IL-4, IL-5, IL-6, IL-9, IL-10, and IL-13 [1] and have been shown to trigger recovery from gastrointestinal nematodes [2]. Nonetheless, mice deficient for IL-4 have been shown to develop residual Th2 responses [3-5] and can expel the nematode Nippostrongylus brasiliensis [6], suggesting that there is a functional equivalent of IL-4 in these processes. IL-13 is a cytokine that shares some, but not all, biological activities with IL-4 [7,8]. There is now compelling evidence that IL-4 and IL-13 share receptor components, including IL-4R alpha and IL-13R alpha 1 [9]. In order to dissect the roles of IL-4 and IL-13 in the regulation of Th2 cells and in the response to nematode infections, we looked for differences between mice deficient for either the IL-4 gene or the IL-4R alpha gene. Unlike IL-4, IL-4R alpha was required for control of N. brasiliensis, and Th2 development during infection--as characterized by cytokine production, GATA-3 and surface CD30 expression--was more severely affected in IL-4R alpha-/- mice than in IL-4-/- mice. Injection of recombinant IL-13 induced worm expulsion in otherwise incompetent RAG2-/- mice. Our results suggest that IL-13 regulates Th2 responses to nematode infection and requires IL-4R alpha.