Age-dependent increase of extrathymic T cells in the liver and their appearance in the periphery of older mice.

The liver is a major site of generation of extrathymic T cells with unique properties (e.g., expressing intermediate TCR and containing self-reactive clones). We investigated herein whether the levels of extrathymic alpha beta T cells varied in various organs as a function of age. A systematic examination of the number of mononuclear cells in various organs of BALB/c mice revealed that the number of hepatic MNC increased with age whereas the number of thymocytes decreased. These changes were more striking in mice fed under conventional conditions than under specific pathogen-free condition. The age-dependent changes in the number of mononuclear cells in the spleen and lymph nodes were minimal. Although the total proportion of alpha beta T cells in each organ remained constant, the staining patterns of TCR-alpha beta as shown by immunofluorescence profiles varied. The most prominent change was that intermediate TCR-alpha beta cells, which constituted a small population in the liver of young mice, expanded in the liver of older mice. Intermediate TCR cells appeared even in the periphery of older mice. These findings were confirmed by the appearance of extrathymic T cells with other unique properties, e.g., double-negative CD4-8- phenotype and CD44 expression. In athymic nude mice, only intermediate TCR cells were present in the liver and periphery. An age-dependent increase of intermediate TCR cells was also seen in these mice. Taken together with the result of bromodeoxyuridine-injection experiment, which showed an intensive in vivo proliferation of cells in the hepatic sinusoids, extrathymic T cells may differentiate predominantly in the liver and appeared even to the periphery in older mice.     

Radioresistance of Intermediate TCR Cells and Their Localization in the Body of Mice Revealed by Irradiation

Extrathymic generation of T cells in the liver and in the intestine was recently demonstrated. We investigated herein whether such T cells, especially those in the liver, are present in other organs of mice. This investigation is possible employing our recently introduced method with which even a minor proportion of extrathymic, intermediate TCR cells in organs other than the liver can be identified. Intermediate TCR cells expressed higher levels of IL-2Rβ and LFA-1 than bright TCR cells (i.e., T cells of thymic origin) as revealed by two-color staining. Although intermediate TCR cells were present at a small proportion in the spleen and thymus, they predominated in these organs after irradiation (9 Gy) and bone marrow reconstitution, or after low dose irradiation (6 Gy). This was due to that intermediate TCR cells were relatively radioresistant, whereas bright TCR cells were radiosensitive. Microscopic observation and immunochemical staining showed that intermediate TCR cells in the spleen localized in the red pulp and those in the thymus localized in the medulla. These intermediate TCR cells displayed a large light scatter, similar to such cells in the liver. The present results suggest that intermediate TCR cells may proliferate at multiple sites in the body.     

Unusual alpha beta-T cells expanded in autoimmune lpr mice are probably a counterpart of normal T cells in the liver.

Autoimmune MRL-lpr/lpr (lpr) mice develop severe lymphadenopathy, characterized by the accumulation of alpha beta-T cells with CD4-8- double negative (DN) phenotype, at the onset of disease. We previously demonstrated that the liver is a major site for the proliferation of such DN alpha beta-T cells. Herein, we further demonstrate that a large proportion of alpha beta-T cells in the liver and other organs, except the thymus, of lpr mice have unique properties, such as DN phenotype, relatively dull TCR intensity, a preponderance of V beta 8+ cells, and Pgp-1 expression. Interestingly, alpha beta-T cells in the liver of normal mice were found to consist of T cells with intermediate intensity of TCR (i.e., brighter than thymic dull TCR and lower than thymic bright TCR) as well as with bright intensity of TCR in the immunofluorescence test. These hepatic alpha beta-T cells with intermediate TCR in normal mice were found to have properties similar to those of alpha beta-T cells in lpr mice. These results suggest that abnormal alpha beta-T cells in lpr mice are a counterpart of normal T cells in the liver. An abnormal expansion of such T cells in the liver might be fundamental to the pathogenesis involved in these autoimmune mice.     

Selective activation of extrathymic T cells in the liver by glycyrrhizin

Extrathymic pathways for T cell differentiation were recently demonstrated in the liver, intestine and omentum. In this study, glycyrrhizin (GL), a plant extract was investigated as to its effect on extrathymic T cells in the liver of mice. A new method using anti-LFA-1 mAb in conjunction with anti-TCR or -CD3 mAbs to sensitively identify such extrathymic T cells is included. Single injection and repeated injections of GL increased not only the number of total hepatic MNC but also the proportion of intermediate TCR cells, which are extrathymic T cells uniquely seen in the liver. In contrast to other tested reagents (e.g., lymphotoxin and estrogen) that activated the extrathymic T cells and simultaneously induced profound thymic atrophy, GL did not affect regular T cells in the thymus. The present results suggest that the selective activation of extrathymic T cells in the liver might be intimately related to the clinical effects of GL.     

A Similar Expression Pattern of Adhesion Molecules between Intermediate TCR Cells in the Liver and Intraepithelial Lymphocytes in the Intestine

Two major populations of extrathymically differentiated T cells exist in the liver and intestine. Such T cells in the liver have TCR of intermediate intensity (i.e., intermediate TCR cells) and constitutively express IL-2 receptor β-chain (IL-2Rβ), whereas those in the intestine, especially intraepithelial lymphocytes, have TCR of bright intensity, consisting of a mixture of IL-2Rβ⁺ and IL-2Rβ^–. All mature thymocytes and thymus-derived T cells seen in the peripheral immune organs are TCR-bright⁺IL-2Rβ^– under resting conditions. When the expression pattern of adhesion molecules, including CD44, L-selectin, LFA-1 and ICAM-1, was compared among these T-cell populations, they displayed quite unique patterns of expression. All extrathymic T cells in the liver, intestine, and even other organs were CD44⁺L-selectin^– LFA-1⁺⁺ICAM-1⁺, whereas thymocytes and thymus-derived T cells were CD44^– L-selectin⁺LFA-1⁺ICAM-1^–. This inverted expression of adhesion molecules between extrathymic T cells and thymus-derived T cells might be associated with their unique tissue-localization.     

Gamma delta TCR cells in hepatic sinusoids and intestinal intraepithelia

We provided here the conception that the liver is an important immune organ after birth. On the other hard, it is well established that the liver in the fetal stage works as a hematopoietic organ. Although a significant number of gamma delta TCR cells are distributed in epithelia of the skin, intestine and reproductive organs, the liver is also one of the most predominant organs of gamma delta TCR cells. The percentages of gamma delta TCR cells in MNC of hepatic sinusoids increased up to 16.0% in young mice aged 4 wk, and approximately 40% of such gamma delta TCR cells expressed the CD8 antigens. V gene segment usage analysis by the PCR method demonstrated that a unique set of V gamma 2/V delta 6 was preferentially used by hepatic gamma delta TCR cells. The predominant appearance of unique gamma delta TCR cells in hepatic sinusoids of mice, including nude mice, proposed us the possibility that these gamma delta TCR cells may differentiate non-thymus dependently in the liver. The lymphocytes in the hepatic sinusoids may be intimately related to the antigens come from the intestine and to the lymphocytes sensitized there. Therefore, we introduced recent evidences about gamma delta T cells in the intestine and discussed their connection with the hepatic gamma delta T cells.     

T cell receptor/CD3-signaling induces death by apoptosis in human T cell receptor gamma delta + T cells.

mAb directed against the TCR/CD3 complex activate resting T cells. However, TCR/CD3 signaling induces death by apoptosis in immature (CD4+CD8+) murine thymocytes and certain transformed leukemic T cell lines. Here we show that anti-TCR and anti-CD3 mAb induce growth arrest of cloned TCR-gamma delta + T cells in the presence of IL-2. In the absence of exogenous IL-2, however, the very same anti-TCR/CD3 mAb stimulated gamma delta (+)-clones to proliferation and IL-2 production. In the presence of exogenous IL-2, anti-TCR/CD3 mAb induced the degradation of DNA into oligosomal bands of approximately 200 bp length in cloned gamma delta + T cells. This pattern of DNA fragmentation is characteristic for the programmed cell death termed apoptosis. These results demonstrate that TCR/CD3 signaling can induce cell death in cloned gamma delta + T cells. In addition, this report is the first to show that apoptosis triggered by TCR/CD3 signaling is not restricted to CD4+CD8+ immature thymocytes and transformed leukemic T cell lines but can be also observed with IL-2-dependent normal (i.e., TCR-gamma delta +) T cells.     

gammadelta T cells may dichotomously modulate infection with avirulent Salmonella choleraesuis via IFN-gamma and IL-13 in mice

To investigate the roles of gammadelta T cells in Salmonella infection, we examined the resolution of an intraperitoneal infection with avirulent Salmonella choleraesuis 31N-1 in mice lacking T-cell-receptor (TCR) alphabeta T cells by disruption of the TCRbeta chain gene (TCRbeta(-/-)). The bacteria in TCRbeta(-/-) mice decreased with kinetics similar to that seen in control mice (TCRbeta(+/+)) after infection. The number of natural killer (NK) cells in the peritoneal cavity increased on day 6 after infection and thereafter decreased in both TCRbeta(-/-) and TCRbeta(+/+) mice, whereas the number of gammadelta T cells, in place of alphabeta T cells, increased remarkably in the peritoneal cavity of TCRbeta(-/-) mice on day 6 after infection. The NK cells from Salmonella-infected TCRbeta(-/-) mice produced interferon-gamma (IFN-gamma) but neither interleukin-4 (IL-4) nor IL-13 in response to immobilized anti-NK1.1 monoclonal antibody (mAb). The gammadelta T cells produced IFN-gamma but neither IL-4 nor IL-13 in response to heat-killed Salmonella, whereas both IFN-gamma and IL-13 but no IL-4 was produced by the gammadelta T cells stimulated with immobilized anti-TCRgammadelta mAb. In vivo administration of anti-NK1.1 mAb inhibited the reduction of Salmonella, whereas anti-TCRgammadelta mAb treatment did not affect the bacterial growth in TCRbeta(-/-) mice after Salmonella infection. However, neutralization of endogenous IL-13 with anti-IL-13 mAb enhanced the bacterial clearance in TCRbeta(-/-) mice after infection. These results suggest that NK1.1(+) cells serve mainly to protect against avirulent Salmonella infection in the absence of alphabeta T cells, whereas gammadelta T cells may play dichotomous roles in Salmonella infection through IFN-gamma and IL-13 in TCRbeta(-/-) mice.     

CD28 delivers a costimulatory signal involved in antigen-specific IL-2 production by human T cells.

CD4+ T cells require two signals to produce maximal amounts of IL-2, i.e., TCR occupancy and an unidentified APC-derived costimulus. Here we show that this costimulatory signal can be delivered by the T cell molecule CD28. An agonistic anti-CD28 mAb, but not IL-1 and/or IL-6, stimulated T cell proliferation by tetanus toxoid-specific T cells cultured with Ag-pulsed, costimulation-deficient APC. Furthermore, the ability of B cell tumor lines to provide costimulatory signals to purified T cells correlated well with expression of the CD28 ligand B7/BB-1. Finally, like anti-CD28 mAb, autologous human APC appeared to stimulate a cyclosporine A-resistant pathway of T cell activation. Together, these results suggest that the two signals required for IL-2 production by CD4+ T cells can be transduced by the TCR and CD28.     

IL-4-producing gamma delta T cells that express a very restricted TCR repertoire are preferentially localized in liver and spleen.

IL-4-producing gamma delta thymocytes in normal mice belong to a distinct subset of gamma delta T cells characterized by low expression of Thy-1. This gamma delta thymocyte subset shares a number of phenotypic and functional properties with the NK T cell population. Thy-1dull gamma delta thymocytes in DBA/2 mice express a restricted repertoire of TCRs that are composed of the V gamma 1 gene product mainly associated with the V delta 6.4 chain and exhibit limited junctional sequence diversity. Using mice transgenic for a rearranged V gamma 1J gamma 4C gamma 4 chain and a novel mAb (9D3) specific for the V delta 6.3 and V delta 6.4 murine TCR delta chains, we have analyzed the peripheral localization and functional properties of gamma delta T cells displaying a similarly restricted TCR repertoire. In transgenic mice, IL-4 production by peripheral gamma delta T cells was confined to the gamma delta+9D3+ subset, which contains cells with a TCR repertoire similar to that found in Thy-1dull gamma delta thymocytes. In normal DBA/2 mice such cells represent close to half of the gamma delta T cells present in the liver and around 20% of the splenic gamma delta T cells.     

Vγ4 γδ T cell-derived IL-17A negatively regulates NKT cell function in Con A-induced fulminant hepatitis

Con A-induced fulminant hepatitis is a well-known animal model for acute liver failure. However, the role of γδ T cells in this model is undefined. In this report, using TCR δ(-/-) mice, we demonstrated a protective role of γδ T cells in Con A-induced hepatitis model. TCR δ(-/-) mice showed significantly decreased levels of IL-17A and IL-17F in the Con A-treated liver tissue, and reconstitution of TCR δ(-/-) mice with wild-type (Wt), but not IL-17A(-/-), γδ T cells significantly reduced hepatitis, strongly suggesting a critical role of IL-17A in mediating the protective effect of γδ T cells. Interestingly, only Vγ4, but not Vγ1, γδ T cells exerted such a protective effect. Furthermore, depletion of NKT cells in TCR δ(-/-) mice completely abolished hepatitis, and NKT cells from Con A-challenged liver tissues of TCR δ(-/-) mice expressed significantly higher amounts of proinflammatory cytokine IFN-γ than those from Wt mice, indicating that γδ T cells protected hepatitis through targeting NKT cells. Finally, abnormal capacity of IFN-γ production by NKT cells of TCR δ(-/-) mice could only be downregulated by transferring Wt, but not IL-17(-/-), Vγ4 γδ T cells, confirming an essential role of Vγ4-derived IL-17A in regulating the function of NKT cells. In summary, our report thus demonstrated a novel function of Vγ4 γδ T cells in mediating a protective effect against Con A-induced fulminant hepatitis through negatively regulating function of NKT cells in an IL-17A-dependent manner, and transferring Vγ4 γδ T cells may provide a novel therapeutic approach for this devastating liver disease.     

IL-7 promotes thymocyte proliferation and maintains immunocompetent thymocytes bearing alpha beta or gamma delta T-cell receptors in vitro: synergism with IL-2

IL-7 induced the proliferation of normal thymocytes and the effect was synergistically potentiated by a small dose of IL-2, which by itself hardly affected thymocyte proliferation. No synergism was observed between IL-7 and any one of the other lymphokines including IL-1, IL-3, and IL-4. The thymocyte culture stimulated with IL-7 and IL-2 consisted of single positive (CD4+CD8- and CD4-CD8+) and double negative (CD4-CD8-) populations, and double positive (CD4+CD8+) cells were completely deleted. Both single positive and double negative thymocytes expressed CD3, but only the former exhibited V beta 8 and V beta 6 in an expected proportion (approximately 30% in BALB/c mice) and the latter none at all. Immunoprecipitation of the cultured thymocytes by anti-TCR gamma antibody, on the other hand, revealed the presence of a TCR gamma chain. Taken together, these results indicated that the thymocyte cultured with IL-7 and IL-2 consisted of mature T cells bearing alpha beta or gamma delta TCR. Experiments using preselected thymocyte subpopulations indicated that double negative cells responded to both IL-7 and IL-2 with positive synergism when combined, while thymocytes enriched for single positive cells preferentially responded to IL-7 with little response to IL-2 and no detectable synergism. Double positive thymocytes showed no proliferation in response to IL-7 and IL-2. In contrast to single positive thymocytes, splenic T cells hardly responded to IL-7, although significant proliferation was induced in the presence of a low dose of IL-2. Thymocytes cultured with IL-7 and IL-2 showed little nonspecific cytotoxic activity, but responded to Con A or alloantigen, whereas those stimulated with a high dose of IL-2 alone exhibited potent cytotoxic activity. These results indicated that IL-7 was involved in the generation of immunocompetent T cells in the thymus in concert with IL-2.     

Differential T cell hyporesponsiveness induced by in vivo administration of intact or F(ab')2 fragments of anti-CD3 monoclonal antibody. F(ab')2 fragments induce a selective T helper dysfunction.

Induction of peripheral T cell anergy associated with stimulation through the TCR complex in vivo has been described in mice using chemically modified APC, staphylococcal enterotoxin B, and intact anti-CD3 mAb. In the latter two models, T cell proliferation, IL-2R expression, and lymphokine production have been demonstrated before subsequent induction of hyporesponsiveness, whereas in the former model, these events have not been observed. To further investigate the relationship between mitogenicity and induction of peripheral hyporesponsiveness, mice were treated with either mitogenic intact anti-CD3 mAb or nonmitogenic F(ab')2 fragments of anti-CD3 mAb. T cells from F(ab')2-treated mice demonstrated a selective decrease in helper functions, with minimal effect on CTL function. Specifically, a marked reduction in ability of Th cells to secrete IL-2 when challenged in vitro with mitogen or alloantigen was observed, which persisted for at least 2 mo after mAb administration and which was independent of T cell depletion. Proliferative function was decreased in CD4+ T cells and could not be fully restored with addition of exogenous IL-2. A helper defect was also evident in vivo, in that F(ab')2-treated mice were deficient in their ability to reject MHC-disparate skin grafts, and in vivo administration of IL-2 reconstituted their ability to reject skin grafts normally. In contrast, T cells from mice treated with intact mAb demonstrated a significant decrease in both CTL and helper functions. A long term reduction in TCR expression on CD4+ cells from F(ab')2-treated mice, and on both CD4+ and CD8+ cells from intact mAb-treated mice was observed. These findings demonstrate that peripheral T cell hyporesponsiveness can be induced in vivo by binding an identical epitope on the TCR complex in the presence or absence of initial proliferation, lymphokine secretion, or IL-2R expression, and that binding to the same epitope can result in varying long term effects on T cell function.     

Adjuvant effect of IL-12: conversion of peptide antigen administration from tolerizing to immunizing for CD8+ T cells in vivo.

CD8+ T cells from TCR transgenic 2C mice, specific for SIYRYYGL peptide bound to H-2Kb, were adoptively transferred into C57BL/6 recipients to allow monitoring of their location, numbers, and phenotype upon peptide challenge. Recipients were primed by s.c. injection of SIYRYYGL alone or with CFA or IL-12, and the transferred cells then tracked by flow cytometry using the 1B2 mAb specific for the 2C TCR. Peptide alone induced a transient and weak expansion of 1B2+ cells in the draining lymph nodes (DLN) by day 3, but these cells were tolerant to secondary peptide challenge. In contrast, priming with CFA/peptide resulted in a large clonal expansion of 1B2+ cells in DLN by day 3, and the cells exhibited a CD25highCD44high phenotype, blast transformation, and lytic effector function. By day 5, 1B2+ cell numbers decreased in the DLN and increased in the spleen and blood. 1B2+ cells with a memory phenotype persisted through day 60 in the DLN, spleen, and blood and responded to secondary peptide challenge. Immunization with peptide, along with IL-12, mimicked the adjuvant effects of CFA with respect to phenotype, clonal expansion, effector function, and establishment of memory. IL-12 was not unique in providing this adjuvant effect however, since CFA/peptide immunization of IL-12-deficient recipient mice also resulted in 1B2+ T cell activation and clonal expansion. Thus, CFA or IL-12 can enhance Ag-specific CD8+ T cell responses to peptide, demonstrating that an inflammatory cytokine(s) can support activation and prevent tolerance induction.     

Regulatory role of peritoneal NK1.1+ alpha beta T cells in IL-12 production during Salmonella infection.

NK1.1+ alpha beta T cells emerge in the peritoneal cavity after an i.p. infection with Salmonella choleraesuis in mice. To elucidate the role of the NK1.1+ alpha beta T cells during murine salmonellosis, mice lacking NK1.1+ alpha beta T cells by disruption of TCR beta (TCR beta-/-), beta 2m (beta 2m-/-), or J alpha 281 (J alpha 281-/-) gene were i.p. inoculated with S. choleraesuis. The peritoneal exudate T cells in wild type (wt) mice on day 3 after infection produced IL-4 upon TCR alpha beta stimulation, whereas those in TCR beta-/-, beta 2m-/-, or J alpha 281-/- mice showed no IL-4 production upon the stimulation, indicating that NK1.1+ alpha beta T cells are the main source of IL-4 production at the early phase of Salmonella infection. Neutralization of endogenous IL-4 by administration of anti-IL-4 mAb to wt mice reduced the number of Salmonella accompanied by increased IL-12 production by macrophages after Salmonella infection. The IL-12 production by the peritoneal macrophages was significantly augmented in mice lacking NK1.1+ alpha beta T cells after Salmonella infection accompanied by increased serum IFN-gamma level. The aberrantly increased IL-12 production in infected TCR beta-/- or J alpha 281-/- mice was suppressed by adoptive transfer of T cells containing NK1.1+ alpha beta T cells but not by the transfer of T cells depleted of NK1.1+ alpha beta T cells or T cells from J alpha 281-/- mice. Taken together, it is suggested that NK1. 1+ alpha beta T cells eliciting IL-4 have a regulatory function in the IL-12 production by macrophages at the early phase of Salmonella infection.     

IL-7 up-regulates IL-4 production by splenic NK1.1+ and NK1.1- MHC class I-like/CD1-dependent CD4+ T cells.

NK T cells are an unusual subset of T lymphocytes. They express NK1. 1 Ag, are CD1 restricted, and highly skewed toward Vbeta8 for their TCR usage. They express the unique potential to produce large amounts of IL-4 and IFN-gamma immediately upon TCR cross-linking. We previously showed in the thymus that the NK T subset requires IL-7 for its functional maturation. In this study, we analyzed whether IL-7 was capable of regulating the production of IL-4 and IFN-gamma by the discrete NK T subset of CD4+ cells in the periphery. Two hours after injection of IL-7 into mice, or after a 4-h exposure to IL-7 in vitro, IL-4 production by CD4+ cells in response to anti-TCR-alphabeta is markedly increased. In contrast, IFN-gamma production remains essentially unchanged. In beta2-microglobulin- and CD1-deficient mice, which lack NK T cells, IL-7 treatment does not reestablish normal levels of IL-4 by CD4+ T cells. Moreover, we observe that in wild-type mice, the memory phenotype (CD62L-CD44+) CD4+ T cells responsible for IL-4 production are not only NK1.1+ cells, but also NK1.1- cells. This NK1.1-IL-4-producing subset shares three important characteristics with NK T cells: 1) Vbeta8 skewing; 2) CD1 restriction as demonstrated by their absence in CD1-deficient mice and relative overexpression in MHC II null mice; 3) sensitivity to IL-7 in terms of IL-4 production. In conclusion, the present study provides evidence that CD4+MHC class I-like-dependent T cell populations include not only NK1.1+ cells, but also NK1.1- cells, and that these two subsets are biased toward IL-4 production by IL-7.     

CD4-mediated signals induce T cell dysfunction in vivo.

Triggering of CD4 coreceptors on both human and murine T cells can suppress TCR/CD3-induced secretion of IL-2. We show here that pretreatment of murine CD4+ T cells with the CD4-specific mAb YTS177 inhibits the CD3-mediated activation of the IL-2 promoter factors NF-AT and AP-1. Ligation of CD4 molecules on T cells leads to a transient stimulation of extracellular signal-regulated kinase (Erk) 2, but not c-Jun N-terminal kinase (JNK) activity. Pretreatment with anti-CD4 mAb impaired anti-CD3-induced Erk2 activation. Costimulation with anti-CD28 overcame the inhibitory effect of anti-CD4 Abs, by induction of JNK activation. The in vivo relevance of these studies was demonstrated by the observation that CD4+ T cells from BALB/c mice injected with nondepleting anti-CD4 mAb were inhibited in their ability to respond to OVA Ag-induced proliferation and IL-2 secretion. Interestingly, in vivo stimulation with anti-CD28 mAb restored IL-2 secretion. Furthermore, animals pretreated with anti-CD4 elicited enhanced IL-4 secretion induced by OVA and CD28. These observations suggest that CD4-specific Abs can inhibit T cell activation by interfering with signal 1 transduced through the TCR, but potentiate those delivered through the costimulatory molecule CD28. These studies have relevance to understanding the mechanism of tolerance induced by nondepleting anti-CD4 mAb used in animal models for allograft studies, autoimmune pathologies, and for immunosuppressive therapies in humans.     

The differentiated state of intestinal lamina propria CD4+ T cells results in altered cytokine production, activation threshold, and costimulatory requirements

Intestinal lamina propria (LP) CD4+ T cells are memory-like effector cells that proliferate at relatively low levels and require high levels of TCR signaling and costimulation for full activation in vitro. To study LP CD4+ T cell functional potential we used DO11.10 TCR transgenic (Tg) mice specific for the class II MHC-restricted OVA323-339 peptide and nontransgenic BALB/c mice. Activation of LP Tg+ T cells with Ag using mucosal explants induced high levels of IL-2, IL-4, and IFN-gamma. Culturing isolated LP cells with IL-12 enhanced IFN-gamma production and down-regulated IL-4 and IL-2, whereas addition of IL-4 maintained IL-4 production without inhibiting IFN-gamma production. Systemic administration of relatively high dose (HD; 100 nM) OVA323-339 peptide induced similar levels of bromodeoxyuridine (BrdU) incorporation by LP and splenic Tg+ T cells in vivo, whereas low dose (LD; 4.5 nM) peptide injections induced 4-fold greater levels of BrdU incorporation for LP compared with splenic Tg+ T cells. Coadministration of CTLA-4Ig reduced BrdU incorporation for splenic cells by 70% with HD and LD stimulation, but had little effect on LP responses to HD stimulation. Results of in vivo studies were confirmed in nontransgenic BALB/c mice using HD (200 microg) and LD (10 microg) anti-CD3 mAb+/- CTLA-4Ig. These results suggest that LP T cells are differentiated effector cells that respond at high levels when activated with relatively low levels of Ag- and B7-mediated costimulation in vivo. The reduced activation threshold of LP T cells may facilitate responses to low levels of Ag derived from mucosal pathogens.     

IL-17A produced by gammadelta T cells plays a critical role in innate immunity against listeria monocytogenes infection in the liver

IL-17A is originally identified as a proinflammatory cytokine that induces neutrophils. Although IL-17A production by CD4(+) Th17 T cells is well documented, it is not clear whether IL-17A is produced and participates in the innate immune response against infections. In the present report, we demonstrate that IL-17A is expressed in the liver of mice infected with Listeria monocytogenes from an early stage of infection. IL-17A is important in protective immunity at an early stage of listerial infection in the liver because IL-17A-deficient mice showed aggravation of the protective response. The major IL-17A-producing cells at the early stage were TCR gammadelta T cells expressing TCR Vgamma4 or Vgamma6. Interestingly, TCR gammadelta T cells expressing both IFN-gamma and IL-17A were hardly detected, indicating that the IL-17A-producing TCR gammadelta T cells are distinct from IFN-gamma-producing gammadelta T cells, similar to the distinction between Th17 and Th1 in CD4(+) T cells. All the results suggest that IL-17A is a newly discovered effector molecule produced by TCR gammadelta T cells, which is important in innate immunity in the liver.     

Effects of in vivo administration of anti-CD3 monoclonal antibody on T cell function in mice. II. In vivo activation of T cells

Anti-CD3 mAb are known to be both immunosuppressive and mitogenic to T cells in vitro. However, only immunosuppression has been observed after in vivo administration of these mAb. The present study demonstrates that T cell activation does occur after in vivo administration of anti-CD3 mAb to mice, evidenced by increased IL-2R expression on T cells, CSF secretion, and extra-medullary hematopoiesis in the spleen. These effects required multivalent cross-linking of the mAb, since F(ab')2 fragments failed to induce them. However, the F(ab')2 fragments did induce modulation of CD3/TCR from the surface of T cells, demonstrating that TCR modulation is not sufficient to induce activation. In addition, interaction of the TCR with either intact or F(ab')2 fragments of the mAb led to increased expression of CD8 in vivo, suggesting that the F(ab')2 fragments of anti-CD3 mAb might be capable of inducing a T cell to undergo some, but not all, of the changes involved in reaching a fully activated state. Further study of the activating effects of anti-CD3 mAb might increase the understanding of the mechanisms of in vivo T cell activation and might also be exploited clinically to stimulate T cell function in immunocompromised states and to enhance hematopoiesis in myelodysplastic disorders.