Staphylococcal enterotoxin B induces anergy to conventional peptide in memory T cells

Microbial superantigens can alter host immunity through aberrant activation and subsequent anergy of responding naive T cells. We show here that the superantigen, staphylococcal enterotoxin B (SEB), directly induces tolerance in memory CD4 T cells. Murine naive and memory CD4(+) T cells were labeled with the fluorescent dye CFSE and the cells were exposed to SEB before they were cultured with specific peptide antigen. Memory, but not naive, T cells became anergic and did not respond to their cognate peptide antigen. The extent and duration of T cell receptor (TCR) clustering was similar to promote naive T cell activation and memory T cell anergy, suggesting similar TCR-SEB interactions led to distinct intracellular signaling processes in the two cell types. Like SEB, soluble anti-CD3 mAb does not stimulate memory cell proliferation. However, unlike SEB, soluble anti-CD3 mAbs did not induce anergy to cognate peptide. Anergy was directly visualized in vivo. CD4(+) memory T cells were identified in mice that had been administered SEB. The cells failed to proliferate in response to subsequent immunization with their cognate recall antigen. Hence, one mode of pathogen survival is the modulation of host immunity through selective elimination of memory T cell responses.     

CTLA-4 is not required for induction of CD8(+) T cell anergy in vivo.

Recent studies of T cell anergy induction have produced conflicting conclusions as to the role of the negative regulatory receptor, CTLA-4. Several in vivo models of tolerance have implicated the interaction of CTLA-4 and its ligands, B7.1 and B7.2, as an essential step in induction of anergy, while results from a number of other systems have indicated that signals from the TCR/CD3 complex alone are sufficient to induce T cell unresponsiveness. One explanation for this disparity is that the requirements for anergy induction depend closely on the details of the system: in vivo vs in vitro, route of stimulus administration, naive vs memory cells, CD4(+) vs CD8(+) cells, etc. To test this possibility, we established an in vivo anergy model using mice transgenic for the 2C TCR on a recombination-activating gene-2-deficient background, that either express or lack the CTLA-4 molecule. This system provides us with a very homogeneous pool of naive Ag-specific CD8(+) T cells, allowing us to control some of the conditions mentioned above. We found that T cells from CTLA-4-deficient mice were anergized by injections of soluble antigenic peptide as efficiently as were CTLA-4-expressing cells. These results indicate that CTLA-4 is not universally required for in vivo T cell anergy induction and may point to distinctions between regulation of peripheral tolerance in CD4(+) and CD8(+) T cells.     

未经刺激的静止CD4+T细胞与克隆CD4+T细胞在抗原特异的及主要组织相容性抗原限制的无能诱导中的差异及其意义

在体外克隆T细胞中,T细胞无能可在多种条件下诱导产生,但T细胞在体内条件下的无能诱导仍有很多疑问和争议。由于正常动物体内对单一抗原特异应答的T细胞频率太低,从体内新提取未经刺激的T细胞进行无能诱导研究一直存在技术上的困难。本文利用HNT—TCR转基因小鼠高度单一的针对HA多肽抗原的CD4^ T细胞群体,以T细胞增殖反应作为检测方法,比较研究了克隆CD4^ T细胞和新提取未经刺激的CD4^ T细胞对无能诱导的反应。结果表明,经化学交联剂l—ethyl-3-3(3-dimethylaminopropyl)carbodiimide(ECDI)处理的抗原提呈细胞(APC)与流感病毒血细胞凝集素(HA)多肽诱导在克隆CD4^ T细胞中产生了无能,这种无能是依赖于特异抗原和主要组织相容性抗原(MHC)的;而在同样条件下,新提取未经刺激的CD4^ T细胞则不能被诱导产生无能。结果提示,体内T细胞与克隆T细胞存在功能上的不同,体内T细胞的无能诱导可能需要不同的条件。这对体内T细胞免疫耐受产生的机制研究和临床应用都有重要意义。     

Host dendritic cells alone are sufficient to initiate acute graft-versus-host disease

Alloantigen expression on host APCs is essential to initiate graft-vs-host disease (GVHD); however, critical APC subset remains to be elucidated. We compared the ability of dendritic cells (DCs) and B cells to initiate acute GVHD by an add-back study of MHC class II-expressing APCs (II(+/+)) into MHC class II-deficient (II(-/-)) mice that were resistant to CD4-dependent GVHD. Injection of host-derived, but not donor-derived, II(+/+) DCs or host-derived II(+/+) B cells, was sufficient to break GVHD resistance of II(-/-) mice and induced lethal acute GVHD. By contrast, host-derived II(+/+) B cells, both naive and LPS stimulated, failed to induce activation or tolerance of donor CD4(+) T cells. Similarly, in a model of CD8-dependent GVHD across MHC class I mismatch injection of allogeneic DCs, but not B cells, induced robust proliferation of donor CD8(+) T cells and broke GVHD resistance of chimeric recipients in which APCs were syngeneic to donors. These results demonstrate that host-derived DCs are critical in priming donor CD4(+) and CD8(+) T cells to cause GVHD, and selective targeting of host DCs may be a promising strategy to prevent GVHD.     

Dendritic cells are sufficient to cross-present self-antigens to CD8 T cells in vivo

The mechanism of cross-presentation enables professional APCs to induce CD8 T cell-mediated immune responses against exogenous Ags. Through this mechanism, APCs can induce either immunity against infectious pathogens or tolerance against self-Ag residing in extralymphatic locations. An unanswered question in this field concerns the identity of the cross-presenting APC. All major classes of professional APCs, particularly dendritic cells, macrophages, and B cells, have previously been shown to be able to cross-present Ags in vitro. In the present study, we have created transgenic mice where MHC class I expression is driven selectively in dendritic cells and provide direct in vivo evidence that dendritic cells are sufficient to cross-present exogenous self-Ags and induce Ag-specific cell division of CD8-positive T cells.     

Human peripheral blood monocyte-derived interleukin-10-induced semi-mature dendritic cells induce anergic CD4(+) and CD8(+) T cells via presentation of the internalized soluble antigen and cross-presentation of the phagocytosed necrotic cellular fragments

We examined the ability of human monocyte-derived interleukin (IL)-10-induced semi-mature dendritic cells (semi-mDCs) that had been pulsed with soluble protein and necrotic cellular fragments to induce an antigen (Ag)-specific anergy in CD4(+) and CD8(+) T cells. IL-10 converted normal immature DCs (iDCs) into semi-mDCs during the maturation. In contrast to normal iDCs and mature DCs, IL-10-induced semi-mDCs as well as IL-10-treated iDCs not only had reduced their allogeneic T cell-stimulatory capacity, but also induced an allogeneic Ag-specific anergy in T cells. Normal mDCs that had been pulsed with tetanus toxin (TT) or allogeneic necrotic cellular fragments caused further activation of TT-specific CD4(+) T cells or allogeneic fibroblast-specific CD8(+) T cells, Ag-pulsed IL-10-induced semi-mDCs induced an anergic state in both cell types. Thus, our results suggest that IL-10-induced semi-mDCs induce an Ag-specific anergy in CD4(+) and CD8(+) T cells via presentation of the internalized protein and cross-presentation of the phagocytosed cellular fragments.     

Induction of CD83+CD14+ nondendritic antigen-presenting cells by exposure of monocytes to IFN-alpha

IFN-alpha is a well-known agent for treatment of viral and malignant diseases. It has several modes of actions, including direct influence on the immune system. We investigated IFN-alpha effects on PBMC in terms of dendritic cell (DC) differentiation, as PBMC are exposed to high IFN-alpha levels during treatment of infections and cancers. We show that in vitro IFN-alpha exposure induced rapid and strong up-regulation of the DC-maturation markers CD80, CD86, and CD83 in bulk PBMC. Consistently, IFN-alpha induced up-regulation of these molecules on purified monocytes within 24 h. Up-regulation of CD80 and CD83 expression was IFN-alpha concentration-dependent. In contrast to GM-CSF + IL-4-generated DCs, most of the IFN-alpha-challenged CD83(+) cells coexpressed the monocyte marker CD14. Despite a typical mature DC immunophenotype, IFN-alpha-treated monocytes conserved phagocytic activity and never acquired a dendritic morphology. In mixed lymphocyte reactions IFN-alpha-treated monocytes were less potent than GM-CSF + IL-4-generated DCs but significantly more potent than untreated monocytes to induce T cell proliferation in bulk PBMC. However, only GM-CSF + IL-4-generated DCs were able to induce a significant proliferation of naive CD4(+) T cells. Notably, autologous memory CD4(+) T cells proliferated when exposed to tetanus toxoid-pulsed IFN-alpha-treated monocytes. At variance with untreated or GM-CSF + IL-4-exposed monocytes, those challenged with IFN-alpha showed long-lasting STAT-1 phosphorylation. Remarkably, CD83(+)CD14(+) cells were present in varicella skin lesions in close contact with IFN-alpha-producing cells. The present findings suggest that IFN-alpha alone promptly generates nondendritic APCs able to stimulate memory immune responses. This may represent an additional mode of action of IFN-alpha in vivo.     

Rapid deletional peripheral CD8 T cell tolerance induced by allogeneic bone marrow: role of donor class II MHC and B cells

Mixed chimerism and donor-specific tolerance are achieved in mice receiving 3 Gy of total body irradiation and anti-CD154 mAb followed by allogeneic bone marrow (BM) transplantation. In this model, recipient CD4 cells are critically important for CD8 tolerance. To evaluate the role of CD4 cells recognizing donor MHC class II directly, we used class II-deficient donor marrow and were not able to achieve chimerism unless recipient CD8 cells were depleted, indicating that directly alloreactive CD4 cells were necessary for CD8 tolerance. To identify the MHC class II(+) donor cells promoting this tolerance, we used donor BM lacking certain cell populations or used positively selected cell populations. Neither donor CD11c(+) dendritic cells, B cells, T cells, nor donor-derived IL-10 were critical for chimerism induction. Purified donor B cells induced early chimerism and donor-specific cell-mediated lympholysis tolerance in both strain combinations tested. In contrast, positively selected CD11b(+) monocytes/myeloid cells did not induce early chimerism in either strain combination. Donor cell preparations containing B cells were able to induce early deletion of donor-reactive TCR-transgenic 2C CD8 T cells, whereas those devoid of B cells had reduced activity. Thus, induction of stable mixed chimerism depends on the expression of MHC class II on the donor marrow, but no requisite donor cell lineage was identified. Donor BM-derived B cells induced early chimerism, donor-specific cell-mediated lympholysis tolerance, and deletion of donor-reactive CD8 T cells, whereas CD11b(+) cells did not. Thus, BM-derived B cells are potent tolerogenic APCs for alloreactive CD8 cells.     

Memory CD8+ T cells protect dendritic cells from CTL killing

CD8(+) T cells have been shown to be capable of either suppressing or promoting immune responses. To reconcile these contrasting regulatory functions, we compared the ability of human effector and memory CD8(+) T cells to regulate survival and functions of dendritic cells (DC). We report that, in sharp contrast to the effector cells (CTLs) that kill DCs in a granzyme B- and perforin-dependent mechanism, memory CD8(+) T cells enhance the ability of DCs to produce IL-12 and to induce functional Th1 and CTL responses in naive CD4(+) and CD8(+) T cell populations. Moreover, memory CD8(+) T cells that release the DC-activating factor TNF-alpha before the release of cytotoxic granules induce DC expression of an endogenous granzyme B inhibitor PI-9 and protect DCs from CTL killing with similar efficacy as CD4(+) Th cells. The currently identified DC-protective function of memory CD8(+) T cells helps to explain the phenomenon of CD8(+) T cell memory, reduced dependence of recall responses on CD4(+) T cell help, and the importance of delayed administration of booster doses of vaccines for the optimal outcome of immunization.     

Schistosoma mansoni worms induce anergy of T cells via selective up-regulation of programmed death ligand 1 on macrophages

Infectious pathogens can selectively stimulate activation or suppression of T cells to facilitate their survival within humans. In this study we demonstrate that the trematode parasite Schistosoma mansoni has evolved with two distinct mechanisms to suppress T cell activation. During the initial 4- to 12-wk acute stages of a worm infection both CD4(+) and CD8(+) T cells are anergized. In contrast, infection with male and female worms induced T cell anergy at 4 wk, which was replaced after egg laying by T cell suppression via a known NO-dependent mechanism, that was detected for up to 40 wk after infection. Worm-induced anergy was mediated by splenic F4/80(+) macrophages (Mphi) via an IL-4-, IL-13-, IL-10-, TGF-beta-, and NO-independent, but cell contact-dependent, mechanism. F4/80(+) Mphi isolated from worm-infected mice were shown to induce anergy of naive T cells in vitro. Furthermore, naive Mphi exposed to live worms in vitro also induced anergy in naive T cells. Flow cytometry on in vivo and in vitro worm-modulated Mphi revealed that of the family of B7 costimulatory molecules, only programmed death ligand 1 (PD-L1) was selectively up-regulated. The addition of inhibitory mAb against PD-L1, but not PD-L2, to worm-modulated Mphi completely blocked the ability of these cells to anergize T cells. These data highlight a novel mechanism through which S. mansoni worms have usurped the natural function of PD-L1 to reduce T cell activation during early acute stages of infection before the subsequent emergence of egg-induced T cell suppression in the chronic stages of infection.     

CD4+ and CD8+ T cells exhibit differential requirements for CCR7-mediated antigen transport during influenza infection

Upon encounter of viral Ags in an inflammatory environment, dendritic cells up-regulate costimulatory molecules and the chemokine receptor CCR7, with the latter being pivotal for their migration to the lymph node. By utilizing mice deficient in CCR7, we have examined the requirement of dendritic cell-mediated Ag transport from the lung to the draining lymph node for the induction of anti-influenza immune responses in vivo. We found that CCR7-mediated migration of dendritic cells was more crucial for CD8(+) T cell than CD4(+) T cell responses. While no specific CD8(+) T cell response could be detected in the airways or lymphoid tissues during the primary infection, prolonged infection in CCR7-deficient mice did result in a sustained inflammatory chemokine profile, which led to nonspecific CD8(+) T cell recruitment to the airways. The recruitment of influenza-specific CD4(+) T cells to the airways was also below levels of detection in the absence of CCR7 signaling, although a small influenza-specific CD4(+) T cell population was detectable in the draining lymph node, which was sufficient for the generation of class-switched anti-influenza Abs and a normal CD4(+) T cell memory population. Overall, our data show that CCR7-mediated active Ag transport is differentially required for CD4(+) and CD8(+) T cell expansion during influenza infection.     

HIV-infected Langerhans cells preferentially transmit virus to proliferating autologous CD4+ memory T cells located within Langerhans cell-T cell clusters

Langerhans cells (LC) are likely initial targets for HIV following sexual exposure to virus and provide an efficient means for HIV to gain access to lymph node T cells. The purpose of this study was to examine the nature of the CD4(+) T cell that becomes infected by HIV-infected LC. We infected human LC within tissue explants ex vivo and then, 3 days later, cocultured HIV-infected LC with different subsets of autologous CD4(+) T cells. Using multicolor flow cytometric analyses of LC-CD4(+) T cell cocultures, we documented that HIV-infected LC preferentially infected memory (as compared with naive) CD4(+) T cells. Proliferating and HIV-infected CD4(+) memory T cells were more frequently detected in conjugates of LC and autologous CD4(+) T cells, suggesting that T cells become activated and preferentially get infected through cluster formation with infected LC, rather than getting infected with free virus produced by single HIV-infected LC or T cells. p24(+) Memory CD4(+) T cells proliferated well in the absence of superantigen; by contrast, p24(+) T cells did not divide or divided only once in the presence of staphylococcal enterotoxin B, suggesting that virus production was rapid and induced apoptosis in these cells before significant proliferation could occur. These results highlight that close interactions between dendritic cells, in this case epidermal LC, and T cells are important for optimal HIV replication within specific subsets of CD4(+) T cells. Disrupting cluster formation between LC and memory CD4(+) T cells may be a novel strategy to interfere with sexual transmission of HIV.     

Peripheral tolerance via the anterior chamber of the eye: role of B cells in MHC class I and II antigen presentation

Ags introduced into the anterior chamber (AC) of the eye induce a form of peripheral immune tolerance termed AC-associated immune deviation (ACAID). ACAID mitigates ocular autoimmune diseases and promotes corneal allograft survival. Ags injected into the AC are processed by F4/80(+) APCs, which migrate to the thymus and spleen. In the spleen, ocular APCs induce the development of Ag-specific B cells that act as ancillary APCs and are required for ACAID induction. In this study, we show that ocular-like APCs elicit the generation of Ag-specific splenic B cells that induce ACAID. However, direct cell contact between ocular-like APCs and splenic B cells is not necessary for the induction of ACAID B cells. Peripheral tolerance produced by ACAID requires the participation of ACAID B cells, which induce the generation of both CD4(+) regulatory T cells (Tregs) and CD8(+) Tregs. Using in vitro and in vivo models of ACAID, we demonstrate that ACAID B cells must express both MHC class I and II molecules for the generation of Tregs. These results suggest that peripheral tolerance induced through the eye requires Ag-presenting B cells that simultaneously present Ags on both MHC class I and II molecules.     

Induction of peripheral T cell tolerance by antigen-presenting B cells. I. Relevance of antigen presentation persistence

Various mechanisms of peripheral T cell tolerization have evolved to avoid responses mediated by autoreactive T cells that have not been eliminated in the thymus. In this study, we investigated the peripheral conditions of Ag presentation required to induce T cell tolerance when the predominant APCs are B cells. We show that transient Ag presentation, in absence of inflammation and in a self-context, induces CD4(+) T cell activation and memory formation. In contrast, chronic Ag presentation leads to CD4(+) T cell tolerance. The importance of long-lasting Ag presentation in inducing tolerance was also confirmed in the herpes stromal keratitis autoimmune disease model. Keratogenic T cells could be activated or tolerized depending on the APC short or long persistence. Thus, when APCs are B cells, the persistence of the Ag presentation itself is one of the main conditions to have peripheral T cell tolerance.     

Airway eosinophils accumulate in the mediastinal lymph nodes but lack antigen-presenting potential for naive T cells

Asthma is characterized by infiltration of the airway wall with eosinophils. Although eosinophils are considered to be effector cells, recent studies have reported their ability to activate primed Th2 cells. In this study, we investigated whether eosinophils are capable of presenting Ag to unprimed T cells in draining lymph nodes (DLN) of the lung and compared this capacity with professional dendritic cells (DC). During development of eosinophilic airway inflammation in OVA-sensitized and challenged mice, CCR3(+) eosinophils accumulated in the DLN. To study their function, eosinophils were isolated from the bronchoalveolar lavage fluid of mice by sorting on CCR3(+)B220(-)CD3(-)CD11c(dim) low autofluorescent cells, avoiding contamination with other APCs, and were intratracheally injected into mice that previously received CFSE-labeled OVA TCR-transgenic T cells. Eosinophils did not induce divisions of T cells in the DLN, whereas DC induced on average 3.7 divisions in 45.7% of T cells. To circumvent the need for Ag processing or migration in vivo, eosinophils were pulsed with OVA peptide and were still not able to induce T cell priming in vitro, whereas DC induced vigorous proliferation. This lack of Ag-presenting ability was explained by the very weak expression of MHC class II on fresh eosinophils, despite expression of the costimulatory molecules CD80 and ICAM-1. This investigation does not support any role for airway eosinophils as APCs to naive T cells, despite their migration to the DLN at times of allergen exposure. DC are clearly superior in activating T cells in the DLN of the lung.     

Th cell-independent immune responses to chimeric hemagglutinin/simian human immunodeficiency virus-like particles vaccine

CD4(+) Th cells are believed to be essential for the induction of humoral and cellular immune responses. In this study we tested the effect and possible mechanisms of the major antigenic component in influenza, hemagglutinin (HA), in helping HIV Env to induce immune responses in CD4(+) T cell knockout (CD4 KO) mice. Simian HIV virus-like particles (SHIV VLPs) or phenotypically mixed chimeric influenza HA/SHIV VLPs were used as immunogens to immunize CD4 KO mice either i.p. or intranasally (i.n.). We found that chimeric HA/SHIV VLPs significantly induced a greater IgG Ab response in both i.p. and i.n. immunized mice and a greater IgA Ab response in mucosal washes in i.n. immunized mice compared with SHIV VLPs. Importantly, chimeric HA/SHIV VLPs induced approximately 3-fold higher neutralizing Ab titers against HIV 89.6 than SHIV VLPs in the absence of CD4(+) T cell help. There was also approximately 40% more specific lysis of the HIV Env-expressing target cells in chimeric HA/SHIV VLP-immunized than in SHIV VLP-immunized CD4 KO mouse splenocytes. Moreover, we have found that chimeric HA/SHIV VLPs could efficiently bind and activate dendritic cells and stimulate the activated dendritic cells to secret TNF-alpha and IFN-gamma. Therefore, chimeric HA/SHIV VLPs could efficiently prime and activate APCs, which could, in turn, induce immune responses in a CD4(+) T cell-independent manner. This study suggests a novel adjuvant role of influenza HA as well as a new strategy to develop more effective therapeutic vaccines for AIDS patients with low CD4(+) T cell counts.     

The potent adjuvant activity of archaeosomes correlates to the recruitment and activation of macrophages and dendritic cells in vivo

The unique glycerolipids of ARCHAEA: can be formulated into vesicles (archaeosomes) with potent adjuvant activity. We studied the effect of archaeosomes on APCs to elucidate the mechanism(s) of adjuvant action. Exposure of J774A.1 macrophages to archaeosomes in vitro resulted in up-regulation of B7.1, B7.2, and MHC class II molecules to an extent comparable to that achieved with LPS. Similarly, incubation of bone marrow-derived DCs with archaeosomes resulted in enhanced expression of MHC class II and B7.2 molecules. In contrast, conventional liposomes made from ester phospholipids failed to modulate the expression of these activation markers. APCs treated with archaeosomes exhibited increased TNF production and functional ability to stimulate allogenic T cell proliferation. More interestingly, archaeosomes enhanced APC recruitment and activation in vivo. Intraperitoneal injection of archaeosomes into mice led to recruitment of Mac1alpha(+), F4/80(+) and CD11c(+) cells. The expression of MHC class II on the surface of peritoneal cells was also enhanced. Furthermore, peritoneal cells from archaeosome-injected mice strongly enhanced allo-T cell proliferation and cytokine production. The ability of archaeosome-treated APCs to stimulate T cells was restricted to Mac1alpha(high), B220(-) cells in the peritoneum. These Mac1alpha(high) cells in the presence of GM-CSF gave rise to both F4/80(+) (macrophage) and CD11c(+) (dendritic) populations. Overall, the activation of APCs correlated to the ability of archaeosomes to induce strong humoral, T helper, and CTL responses to entrapped Ag. Thus, the recruitment and activation of professional APCs by archaeosomes constitutes an efficient self-adjuvanting process for induction of Ag-specific responses to encapsulated Ags.     

Alloreactive memory T cells are responsible for the persistence of graft-versus-host disease

Graft-vs-host disease (GVHD) is caused by a donor T cell anti-host reaction that evolves over several weeks to months, suggesting a requirement for persistent alloreactive T cells. Using the C3H.SW anti-C57BL/6 (B6) mouse model of human GVHD directed against minor histocompatibility Ags, we found that donor CD8(+) T cells secreting high levels of IFN-gamma in GVHD B6 mice receiving C3H.SW naive CD8(+) T cells peaked by day 14, declined by day 28 after transplantation, and persisted thereafter, corresponding to the kinetics of a memory T cell response. Donor CD8(+) T cells recovered on day 42 after allogeneic bone marrow transplantation expressed the phenotype of CD44(high)CD122(high)CD25(low), were able to homeostatically survive in response to IL-2, IL-7, and IL-15 and rapidly proliferated upon restimulation with host dendritic cells. Both allogeneic effector memory (CD44(high)CD62L(low)) and central memory (CD44(high)CD62L(high)) CD8(+) T cells were identified in B6 mice with ongoing GVHD, with effector memory CD8(+) T cells as the dominant (>80%) population. Administration of these allogeneic memory CD8(+) T cells into secondary B6 recipients caused virulent GVHD. A similar allogeneic memory CD4(+) T cell population with the ability to mediate persistent GVHD was also identified in BALB/b mice receiving minor histocompatibility Ag-mismatched B6 T cell-replete bone marrow transplantation. These results indicate that allogeneic memory T cells are generated in vivo during GVH reactions and are able to cause GVHD, resulting in persistent host tissue injury. Thus, in vivo blockade of both alloreactive effector and memory T cell-mediated host tissue injury may prove to be valuable for GVHD prevention and treatment.     

The CXC chemokine murine monokine induced by IFN-gamma (CXC chemokine ligand 9) is made by APCs,targets lymphocytes including activated B cells,and supports antibody responses to a bacterial pathogen in vivo

Monokine induced by IFN-gamma (Mig; CXC chemokine ligand 9) is an IFN-gamma-inducible CXC chemokine that signals through the receptor CXCR3 and is known to function as a chemotactic factor for human T cells, particularly following T cell activation. The mig gene can be induced in multiple cell types and organs, and Mig has been shown to contribute to T cell infiltration into immune/inflammatory reactions in peripheral tissues in mice. We have investigated the expression and activities of Mig and CXCR3 in mouse cells and the role of Mig in models of host defense in mice. Murine (Mu)Mig functioned as a chemotactic factor for resting memory and activated T cells, both CD4(+) and CD8(+), and responsiveness to MuMig correlated with surface expression of MuCXCR3. Using mig(-/-) mice, we found that MuMig was not necessary for survival after infections with a number of intracellular pathogens. Surprisingly, however, we found that mig(-/-) mice showed reductions of 50-75% in Abs produced against the intracellular bacterium Francisella tularensis live vaccine strain. Furthermore, we found that MuMig induced both calcium signals and chemotaxis in activated B cells, and that B cell activation induced expression of MuCXCR3. In addition, IFN-gamma induced the expression of mumig in APCs, including CD8 alpha(+) and CD8 alpha(-) dendritic cells. Together, our data suggest that Mig and CXCR3 may be important not only to recruit T cells to peripheral inflammatory sites, but also in some cases to maximize interactions among activated T cells, B cells, and dendritic cells within lymphoid organs to provide optimal humoral responses to pathogens.