Induction of Thymus-Derived γδ T Cells by Escherichia coli Enterotoxin B Subunit in Peritoneal Cavities of Mice

We examined the activation of intraperitoneal T cells in BALB/c mice by the Escherichia coli enterotoxin B subunit, which induced a specific Th2 type of T-cell response to intraperitoneally coadministered bovine immunoglobulin G. The numbers of both γδ and αβ T cells increased significantly after intraperitoneal administration of the B subunit in a time-dependent manner; these numbers were not affected by the B-subunit G33D mutant, which is defective in GM₁ ganglioside-binding ability. Early after administration a small number of γδ T cells produced either interleukin-4 (IL-4) or gamma interferon, while late after administration primarily IL-10-producing γδ T cells were detected. γδ T cells induced by the B subunit did not express a characteristic V gene over the time course of the study. The induction of γδ T cells did not occur in athymic nu/nu mice but could be induced upon transplantation of fetal AKR thymus-like αβ T cells. γδ T cells in athymic nu/nu mice with a fetal thymic graft predominantly expressed the donor Thy-1.1 antigen but not the host Thy-1.2 antigen. The induction of these T cells, however, could not be restored by coadministration of the B subunit with peritoneal cells from normal mice. These results suggest that the B subunit activates intraperitoneal γδ and αβ T cells in a manner dependent upon its ability to bind to GM₁ ganglioside. γδ T cells induced by the B subunit are Th2-type cells derived from the thymus. These γδ T cells may be functionally involved in specific Th2 responses to the B subunit, which possibly acts as an adjuvant through the influence of αβ T cells.     

A tuberculosis vaccine based on phosphoantigens and fusion proteins induces distinct gammadelta and alphabeta T cell responses in primates

Phosphoantigens are mycobacterial non-peptide antigens that might enhance the immunogenicity of current subunit candidate vaccines for tuberculosis. However, their testing requires monkeys, the only animal models suitable for gammadelta T cell responses to mycobacteria. Thus here, the immunogenicity of 6-kDa early secretory antigenic target-mycolyl transferase complex antigen 85B (ESAT-6-Ag85B) (H-1 hybrid) fusion protein associated or not to a synthetic phosphoantigen was compared by a prime-boost regimen of two groups of eight cynomolgus. Although phosphoantigen activated immediately a strong release of systemic Th1 cytokines (IL-2, IL-6, IFN-gamma, TNF-alpha), it further anergized blood gammadelta T lymphocytes selectively. By contrast, the hybrid H-1 induced only memory alphabeta T cell responses, regardless of phosphoantigen. These latter essentially comprised cytotoxic T lymphocytes specific for Ag85B (on average + 430 cells/million PBMC) and few IFN-gamma-secreting cells (+ 40 cells/million PBMC, equally specific for ESAT-6 and for Ag85B). Hence, in macaques, a prime-boost with the H-1/phosphoantigen subunit combination induces two waves of immune responses, successively by gammadelta T and alphabeta T lymphocytes.     

gammadelta T cells contribute to the systemic immunoglobulin E response and local B-cell reactivity in allergic eosinophilic airway inflammation

Allergic airway inflammation induced in mice is T-cell dependent and recruitment of eosinophils to airspaces requires both alphabeta and gammadelta T cells. From previous studies it is evident that alphabeta T cells are essential for the allergic T helper type 2 (Th2)-like response, while the mechanistic contribution of gammadelta T cells is still unclear. In this study, we have investigated the role of gammadelta T cells in allergic airway eosinophilia induced by ovalbumin hypersensitivity. By comparing the responsiveness to sensitizing allergen of wild-type mice with that of T-cell receptor gammadelta knockout mice (TCRgammadelta KO) we demonstrated that mice lacking gammadelta T cells are defective in the systemic ovalbumin-specific immunoglobulin E (IgE) response. Furthermore, after aerosol challenge with allergen, gammadelta T-cell deficient mice exhibited a significantly decreased migration of B cells and natural killer cells to airways and reduced levels of allergen-specific IgG and IgA in bronchoalveolar lavage fluid. The role for B cells in the airway inflammation was indicated by the impaired ability of mice lacking functional B cells to evoke an eosinophilic response. The diminished eosinophilia in TCRgammadelta KO mice could not be explained by a defective Th2 activation since these mice displayed a normal IgG response in serum and an unaffected IG2b/IgG1 ratio in airways. Analysis of immunoregulatory cytokines in isolated lung tissue, thoracic lymph nodes and spleen further supported the notion that these mice are able to evoke a sufficient activation of T helper cells and that gammadelta T cells are not required for maintaining the Th2 profile. These results indicate that gammadelta T cells contribute to allergic airway inflammation by pathways separate from classical Th2 immune activation.     

Role of interleukin-4 in down-regulation of contact sensitivity by gammadelta T cells from tolerized T-cell receptor alpha-/- mice.

Contact sensitivity (CS) is a classical example of an in vivo T-cell-mediated immune response that is under regulation. Such down-regulation can be mediated by alphabeta T cells in mice that are tolerized by prior exposure to high doses of antigen. In contrast, we demonstrated previously that such high-dose antigen tolerance in T-cell receptor (TCR) alpha-/- H-2d mice induced antigen-specific, apparently major histocompatibility complex-unrestricted, CD4- CD8- gammadelta T cells, that also could down-regulate CS responses antigen-specifically in vivo, and also inhibited in vitro production of IFN-gamma. In the present experiments we employed H-2b-deficient TCRalpha-/- and TCRbeta-/- mice, owing to different molecular constructs than were used previously, and confirmed that tolerized gammadelta T cells in these different H-2b alphabeta TCR-/- mice down-regulated CS. Thus, gammadelta T-cell suppressor function was not limited to mice bearing a special transgenic TCRalpha-/- DNA construct. Furthermore, employing monoclonal antibody and complement depletion in vitro and adoptive transfer in vivo, characterized the phenotype of these gammadelta down-regulatory T cells as: CD3+, CD28+, CD40-ligand+, Fas+, FcgammaR+ and NK1.1-. Also, in vitro antigen desensitization of these trinitrophenyl (TNP)-specific TCRgammadelta+ down-regulatory cells was achieved with soluble TNP-bovine serum albumin (BSA), but not with oxazolone-BSA, showing that these suppressive gammadelta T cells have antigen-specific receptors. Moreover, employing monoclonal antibody blocking of gammadelta suppressors in vitro, and of recipients in vivo, we showed that interleukin-4 (IL-4) was involved in this down-regulation of CS by gammadelta T cells, while IL-10 and transforming growth factor-beta2 were not. In summary, generation of antigen-specific, double-negative, gammadelta suppressor cells, by tolerance of high antigen doses in TCRalpha-/- mice, appears to be a general phenomenon, and IL-4 production is involved in their down-regulation of the T helper type 1 cells that mediate CS.     

Gammadelta T cells assist alphabeta T cells in the adoptive transfer of contact hypersensitivity to para-phenylenediamine

Para-phenylenediamine (PPD) is known to be a common sensitizer of allergic contact dermatitis and contact urticaria. To clarify the mechanism of contact hypersensitivity (CHS) to PPD, we established a mouse model of PPD-induced CHS. BALB/c mice were immunized for 3 consecutive days by painting topically a 2.5% PPD solution on their shaved abdominal skin. On days 5, 7 or 9 after the initial application, the mice were challenged by applications of a 2.5% PPD solution. Maximal ear swelling was determined at 24 h but another statistically significant and smaller ear swelling was observed 1 h after challenge with PPD in a hapten-specific manner. Adoptive cell transfer experiments demonstrated that the ear swelling of the adoptive cell transferred mice displayed an early response at 6 h and a late response from 12 h to 24 h when the recipient mice were challenged immediately after transfer. Both MoAbs and complement treatment of the transferred cells demonstrated that the phenotype of the early response cells which elicited a response at 6 h after challenge was Thy1(+), B220(+), alphabeta TCR(-), gammadelta TCR(-), CD3(-), CD4(-), CD5(+) and CD8(-). The in vitro treatment of effector cells with MoAbs against not only alphabeta TCR but also gammadelta TCR, together with complement, was found to diminish substantially the late response, elicited 12-24 h after challenge. Gammadelta T cells reconstituted the ability of alphabeta T cells to transfer 24 h CHS responsiveness. The phenotype of the gammadelta T cells that assist CHS effector alphabeta T cells was CD3(+), CD4(-) and CD8(+) and these regulatory gammadelta T cells were neither Ag-specific nor MHC-restricted. Furthermore, gammadelta T cells from normal spleen could also assist alphabeta T cells in adoptive transfer of the 24 h CHS response in a non-MHC-restricted manner. RT-PCR demonstrated that alphabeta T cells strongly expressed mRNA IFN-gamma, whereas gammadelta T cells expressed not only IFN-gamma but also IL-4 and IL-10. These data indicate that not only early response cells and alphabeta T cells but also Th2 type gammadelta T cells may play an important role in the elicitation of CHS to PPD.     

Persistent infection with Listeria monocytogenes in the kidney induces anti-inflammatory invariant fetal-type gammadelta T cells

After intraperitoneal inoculation with Listeria monocytogenes, gammadelta T cells appear in the peritoneal cavity preceding the appearance of alphabeta T cells. Such gammadelta T cells predominantly express T-cell receptor (TCR)Vgamma1/Vdelta6, develop through an extrathymic pathway, and contribute to host defence against the bacteria. We have observed a gradual increase in gammadelta T cells in kidneys of mice after intrarenal inoculation with L. monocytogenes, which resulted in an unusually long-lasting local infection. In this study, we examined the characteristics and the roles of the gammadelta T cells induced in this model. It was found that these gammadelta T cells predominantly expressed TCRVgamma6/Vdelta1 with canonical junctional sequences identical to those expressed on fetal thymocytes. Although depletion of such gammadelta T cells in vivo did not affect the number of bacteria, it resulted in histologically exacerbated inflammation in the kidneys. These results indicate that a persistent infection with L. monocytogenes in kidneys induces a different kind of gammadelta T cell from that induced after intraperitoneal infection. The former expresses invariant fetal-type Vgamma6/Vdelta1+TCR and plays a regulatory role in resolution of inflammation.     

gammadelta T cells: an important source of IL-17

IL-17 is a cytokine that plays an important role in orchestrating innate immune function. In addition, IL-17 has been shown to exacerbate autoimmune diseases. CD4(+) alphabeta T cells, gammadelta T cells, and NK cells all produce IL-17. Th17 cells are a newly defined alphabeta(+) T cell lineage characterized by IL-17 production. However, gammadelta T cells are often the major source of this cytokine. Their response can be very rapid during bacterial infections and has been shown to be protective, but IL-17-producing gammadelta T cells have also been found to exacerbate collagen-induced arthritis. Interestingly, some gammadelta T cells produce IL-17 in response to IL-23 alone, even in na?ve animals, suggesting they are already differentiated and may develop differently than CD4(+) alphabeta Th17 cells.     

Analysis of CD3 and antigen receptor expression on T cell subpopulations of aged athymic mice

The expression of the T cell antigen receptor on subpopulations of extrathymically generated T cells from athymic mice was investigated and compared to antigen receptor expression in normal mice. To this end, spleen and lymph node cells from 18 individual athymic BALB/c nu/nu mice between 6 and 12 months of age and from normal controls were enriched for T cells by nylon wool filtration. Expression of the following cell surface markers was analyzed by two-color flow cytometry: Thy-1, CD4, CD8, V beta 8 and CD3. The distribution of subpopulations as defined by these markers varied much more among athymic than among normal mice. Some recurrent patterns did, however, occur that may be characteristic of the extrathymic pathway of T cell differentiation in nu/nu mice. Among Thy-1.2+ cells, CD8+ cells predominated over CD4+ cells. No CD4+8+ "double positive" cells were found, but CD4-8- "double negative" cell constituted 16% on average. All nu/nu nylon wool-nonadherent cells expressing Thy-1 at a normal level also expressed CD3, whereas Thy-1low and Thy-1- cells were CD3-. The fraction of V beta 8 T cells among the CD4+ and CD8+ subsets was near to normal in the majority of these animals. Most interestingly, the density of V beta 8 and CD3 expression was lower in athymic than in euthymic animals. This level of T cell antigen receptor expression was, however, higher than on immature CD4+8+ thymocytes. A fraction of the nude T cells presently characterized responded with proliferation to both anti-T cell receptor V beta 8 monoclonal antibody and to concanavalin A. Despite their apparently normal phenotype (with the exception of reduced T cell receptor expression), this response was, however, 4 to 10 times smaller than that of normal control cells. The presently described Thy-1+ T cell receptor intermediate cells may either be a(n) aberrant lineage(s) only generated extrathymically, or represent the accumulation of an immature intermediate stage of normal (i.e. thymic) T cell differentiation.     

Recombinant interleukin-2 inhibits growth of human tumor xenografts in congenitally athymic mice

Administration of human recombinant interleukin-2 (RIL-2) into congenitally athymic (nu/nu) mice carrying subcutaneous transplants of HeLa, HU 609T and T24B human carcinoma cells partially inhibited growth of the human tumor xenografts. In vitro activation of nu/nu spleen cells with human RIL-2 resulted in generation of killer cells showing in the 51Cr cytotoxicity assay similar levels of cytolysis as RIL-2-activated spleen cells from heterozygous (nu/+) mice. The RIL-2-activated (LAK) cells were cytotoxic for a variety of mouse and human tumors, reaching the peak of their cytotoxic activity after 3 days of cultivation in the RIL-2-containing medium. The cytotoxic activity of activated nu/nu spleen cells was significantly reduced by treatment with antibody against glycolipid asialo GM1, the differentiation antigen of natural killer (NK) cells. This finding suggests that in addition to the conventional, asialo GM1- LAK cells, asialo GM1+ activated NK cells participated in the cytotoxicity displayed by the IL-2-activated nu/nu killer spleen cells.     

Collagen-induced arthritis development requires alpha beta T cells but not gamma delta T cells: studies with T cell-deficient (TCR mutant) mice.

Collagen type II (CII)-induced arthritis (CIA) in mice is a model for rheumatoid arthritis (RA) in which the role of T lymphocytes remains controversial. To clarify this, we have bred a targeted gene deletion of TCR beta or delta loci into two mouse strains susceptible to CIA, the B10.Q and DBA/1 strains. The TCRbeta-/- mice lacked alphabeta T cells, which was compensated by an expansion of B cells, gammadelta T cells and NK cells. The beta-/- mice, but not control beta+/- littermates, were completely resistant to CIA. The production of anti-CII IgG antibodies was also abolished in beta-/- mice, revealing a strict alphabeta T cell dependency. In contrast, beta-/- mice produced reduced, but significant, anti-CII IgM titers after immunization with either CII or ovalbumin, indicating a multispecificity for these alphabeta T cell-independent IgM antibodies. The TCRdelta-/- mice lacked gammadelta T cells but had no other significant changes in lymphocyte or monocyte subsets. The cytokine response (IL-2, IL-4, IL-10 and IFN-gamma) in delta-/- mice, quantified by flow cytometry staining of mitogen-stimulated lymphocytes, was indistinguishable from normal mice. Likewise, no statistically significant differences were observed in CIA between mice lacking gammadelta T cells and control littermates, considering arthritis incidence, day of disease onset, maximum arthritic score, anti-CII IgG titers and disease course. We conclude that alphabeta T cells are necessary for CIA development and for an IgG response towards CII, whereas gammadelta T cells are neither necessary nor sufficient for development of CIA.     

γδ T cells are critical for the induction of anterior chamber-associated immune deviation

Anterior chamber-associated immune deviation (ACAID) is a systemic form of tolerance that is elicited by introducing antigens into the anterior chamber of the eye. ACAID is characterized by deficiencies in delayed-type hypersensitivity and complement-fixing antibodies upon subsequent challenge with antigen. The mechanisms responsible for the generation of this form of tolerance are not yet completely clear. Here we asked whether gammadelta T cells, which are critical in the induction of oral tolerance and nasal tolerance, play a role in ACAID. The percentage of splenic gammadelta T cells was higher in mice that received antigen via the anterior chamber compared to untreated mice. In addition, CD44 was up-regulated on some splenic gammadelta and alphabeta T cells after the intraocular injection of antigen. Moreover, administration of antigen into the anterior chamber did not induce ACAID in the C57BL/6 mice pretreated with anti-mouse delta-chain monoclonal antibody or in the gammadelta T-cell-receptor-deficient (delta-/-) mice. gammadelta T cells from wild-type mice reconstituted ACAID when transferred into the delta-/- mice before injection of antigen, verifying that the deficiency in delta-/- mice results from the lack of gammadelta T cells rather than from an inadvertent change caused by deletion of the delta-chain. These findings indicate that gammadelta T cells play a very important role in ocular tolerance.     

Downregulation of innate and acquired antitumor immunity by bystander gammadelta and alphabeta T lymphocytes with Th2 or Tr1 cytokine profiles.

It has been thought that natural killer (NK) cells appearing early in tumor lesions play a pivotal role in the innate immunity against tumor cells. Although NK cells serve as the first tumoricidal effector cells, they subsequently promote a shift in effectors from themselves to tumor-specific cytotoxic T lymphocytes (CTLs) that mediate the acquired immunity. The mechanism of this shift has not been fully elucidated, however, NK cell-derived T helper (Th) 1 cytokines such as interferon (IFN)-gamma seem to play a key role. Another NK-lineage, termed natural killer T (NK T) cells, may also participate in the innate period when they acquire the ability to secrete Th1 cytokines. Interleukin-4 (IL-4) and IL-10, belonging to Th2, and transforming growth factor-beta (TGF-beta), belonging to T regulatory (Tr) 1 cytokines, are known to suppress the development of NK, NK T cells, as well as CTLs and to block Th0 cell differentiation to Th1 cells, suggesting that tumor cells can evade the innate and acquired immunity by virtue of cells producing these inhibitory cytokines. In early tumor lesions of murine B16 melanoma, gammadelta T and alphabeta intermediate (int) T cells that co-infiltrate with NK and NK T cells can produce Th2 cytokines and inhibit the innate immunity. In MM2 mammary tumor-bearing mice, gammadelta T cells appearing both lesionally and systemically secrete Tr1-type cytokines and depress the acquired immunity. These Th2- or Tr1-type gammadelta T and alphabeta(int) T cells downregulate the tumoricidal cells by means of both their secreted cytokines and express major histocompatibility complex (MHC) class I molecules.     

The role of γδ T cells in the airways

Based on their T cell receptor expression two distinct T cell populations have been identified and designated as alphabeta and gammadelta T cells. While the specific role of alphabeta T cells is well understood, the specific function of gammabeta T cells remains elusive. Despite the limited knowledge on what gammadelta T cells exactly recognize as their antigen or antigens, several studies have clearly demonstrated that gammadelta T cells are important regulators of immune responses. Studies on gammadelta T cells in the lung have shown that gammadelta T cells influence B and T cell responses. For instance, gammadelta T cells modulate CD4+alphabeta T cells in tuberculosis, and in allergic inflammation they support IgE production. Furthermore, a recent study on their role as part of the innate immune response has demonstrated that gammadelta T cells regulate airway function independently of alphabeta T cells. This novel finding provides an opportunity to review previous studies on gammadelta T cells in the lung of mice and humans. The examination of these data demonstrates that understanding the role of the various subsets of gammadelta T cells will be critical in elucidating their function as "immunosurveillance cells" of the lung.     

Thymic rudiments are responsible for induction of functional T cells in nu/nu mice

Congenitally athymic nude (nu/nu) mice have been thought to exhibit no T cell functions despite the presence of some Thy-1 positive (Thy-1+) cells. However, we detected a significant number of Con A-responsive cells in spleens of nu/nu mice after the age of 2 months when the spleen cells were cultured in a medium containing 5% human plasma or human serum, but not when they were cultured in fetal calf serum. Cytotoxic test using anti-Thy-1.2 antibody plus complement has revealed that these Con A-responsive cells are indeed Thy-1+. The Con A-responsive T cells increase with age. PHA-responsive and alloreactive T cells are also detected in the spleens of 11-month-old nu/nu mice. To probe the origins of the T-lymphocytes of the nu/nu mice we examined extensively and systematically the thymic remnants in the mediastinum and neck region of the nu/nu mice in search for T cell development in thymic rudiments. In these investigations we regularly found small accumulations of cells comprising almost entirely Thy-1+ lymphocytes surrounding accumulations surrounded by epithelial cells. These findings suggest that apparent sites of T cell development in thymic rudiments are indeed present in nude mice and appear to be functioning to induce expression T cell markers on precursor cells in the lymphoid lineage. Together with our prior findings the evidence presented in this report shows that a pathway exists in nude mice. In the converse these findings suggest that the thymus is the sole site for induction of the differentiation of stem cells or precursor T cells into mature T-lymphocytes. The findings suggest that indications of alternative differentiation pathways for T-lymphocytes must seek the location of these pathways within the thymus itself.     

T-cell-independent responses to Borrelia burgdorferi are critical for protective immunity and resolution of lyme disease

The humoral immune response to Borrelia burgdorferi during persistent infection is critical to both protective and disease-resolving immunity. This study examined the role of B cells in the absence of T cells during these events, using mice with selected immune dysfunctions. At 6 weeks postinfection, an interval at which arthritis resolves in immunocompetent mice, arthritis severity was equivalent among immunocompetent mice, alphabeta(+)-T-cell-deficient mice, and mice lacking both alphabeta(+) and gammadelta(+) T cells. Arthritis severity was worse in SCID mice, which lack T and B lymphocytes. Carditis regressed in immunocompetent mice and those lacking both alphabeta(+) and gammadelta(+) T cells but remained active in mice lacking only alphabeta(+) T cells and in SCID mice. Mice lacking only alphabeta(+) T cells and those lacking both alphabeta(+) and gammadelta(+) T cells generated immunoglobulin M (IgM) and IgG3 B. burgdorferi-reactive antibodies. Sera from infected immunocompetent mice, mice lacking only alphabeta(+) T cells, and mice lacking both alphabeta(+) and gammadelta(+) T cells passively protected naive mice against challenge inoculation with B. burgdorferi. However, only sera from infected immunocompetent mice, but not sera from infected T-cell-deficient mice, were able to resolve arthritis when passively transferred to actively infected SCID mice. These data demonstrate that B-cell activation during a T-cell-independent response may be critical for resolution of arthritis and carditis and that protective antibodies are generated during this response.     

Live varicella vaccine polarizes the mucosal adjuvant action of cholera toxin or its B subunit on specific Th1-type helper T cells with a single nasal coadministration in mice

This study was undertaken to determine whether the specific Th1- or Th2-cell response to varicella-zoster virus was induced predominantly by a mucosal adjuvant, cholera toxin, in mice. A commercially available live varicella vaccine (Oka strain) and cholera toxin or its B subunit were administered simultaneously via the nasal route. Delayed-type hypersensitivity to the Oka vaccine was induced, but the systemic neutralizing antibody response was low. The delayed-type hypersensitivity evoked after a single administration was relatively higher than that on administration three times. When spleen cells from mice immunized once with the vaccine and cholera toxin or its B subunit were restimulated with the live vaccine in vitro, there was greater thymidine uptake and production of interleukin- 2 (IL-2) than controls, but only a low level of IL-4 production. The production of IL-2 induced by the B subunit of cholera toxin was less than that by cholera toxin and a mutant of Escherichia coli enterotoxin on co-immunization with the vaccine in mice. Cholera toxin and its B subunit have been reported to induce predominantly a specific Th2-type T-cell response to various antigens. However, the Oka vaccine is an antigen that polarizes the activation of specific Th1/Th2-type T cells by cholera toxin or its B subunit to the Th1-type side. Cholera toxin and its B subunit are thus useful mucosal adjuvants for inducing cellular immunity to the Oka vaccine similar to Escherichia coli enterotoxin.     

Regulation of alphabeta/gammadelta T cell lineage commitment and peripheral T cell responses by Notch/RBP-J signaling

RBP-J is a key mediator of Notch signaling that regulates a large spectrum of cell fate determinations. To elucidate the functions of Notch signaling in T cell development, we inactivated RBP-J specifically at two stages of T cell development by crossing RBP-J floxed mice with lck-cre or CD4-cre transgenic mice. The loss of RBP-J at an earlier developmental stage resulted in enhanced generation and accelerated emigration of gammadelta T cells, whereas alphabeta T cell development was arrested at the double-negative 3 stage. The loss of RBP-J at a later stage did not affect the absolute number or the production rate of CD4 or CD8-positive mature T cells but enhanced Th1 cell response and reduced CD4(+) T cell proliferation. Our data demonstrated that Notch/RBP-J signaling regulates gammadelta T cell generation and migration, alphabeta T cell maturation, terminal differentiation of CD4(+) T cells into Th1/Th2 cells, and activation of T cells.     

Gammadelta T cells do not require fully functional cytotoxic pathways or the ability to recognize recipient alloantigens to prevent graft rejection.

Gammadelta T cells are a unique and minor T-cell subset that differs from conventional alphabeta T cells by virtue of their tissue localization and antigen processing requirements. We have previously shown that ex vivo-activated gammadelta T cells are able to prevent graft rejection without causing clinically significant graft-versus-host disease (GVHD). In the present study, we examined how gammadelta T cells facilitate alloengraftment and to what extent mechanisms used by conventional alphabeta T cells are also used by gammadelta T cells. We observed that, unlike alphabeta T cells, for which CD8(+) T cells are primarily responsible for facilitating engraftment, purified CD8(+)gammadelta(+) T cells administered at the same fractional dose as for the unseparated activated gammadelta T-cell population were insufficient to prevent graft rejection. Furthermore, the ability to prevent graft rejection was not affected by the absence of fully functional fas ligand or perforin cytotoxic pathways, nor was it contingent on the ability of gammadelta T cells to recognize recipient major histocompatibility process alloantigens. Repetitive infusions of a suboptimal dose of gammadelta T cells however were able to rescue mice from graft rejection, suggesting that the persistence of these cells in vivo was critical in facilitating alloengraftment. These studies demonstrate that gammadelta T cells do not use mechanisms used by conventional nontolerant alphabeta T cells to prevent graft rejection. The ability of these cells to promote engraftment without causing GVHD further distinguishes these cells from alphabeta T cells and may be an attribute that can be exploited in the clinical transplantation setting.     

Thymus-derived cytokine(s) including interleukin-7 induce increase of T cell receptor α/β+ CD4−CD8− T cells which are extrathymically differentiated in athymic nude mice

Extrathymic T cell differentiation pathways have been reported, although the thymus is the main site of T cell differentiation. The thymus is also known to produce several cytokines that induce proliferation of thymocytes. In the present study, we investigated the influence of thymus-derived cytokines on extrathymic T cell differentiation by intraperitoneal implantation with a diffusion chamber which encloses fetal thymus (we named it fetal thymus-enclosed diffusion chamber, FTEDC) in athymic BALB/c nu/nu mice. Increase in number of T cells bearing T cell receptor (TcR) α/β was detected in lymph nodes and spleens of FTEDC-implanted nude mice 1 week after implantation, whereas no such increase was detected in control nude mice implanted with a diffusion chamber without thymus. The FTEDC-induced increase of T cells was suppressed by intraperitoneal injection of anti-interleukin-7 monoclonal antibody (mAb). The TcR α/β T cells in FTEDC-inplanted BALB/c nu/nu mice preferentially expressed Vβ11, although Vβ11-positive T cells are deleted in the thymus of euthymic BALB/c mice by clonal elimination of self-superantigen Dvb 11-specific T cells. TcR α/β T cells in FTEDC-implanted nude mice were of CD4^?CD8^? phenotype and showed no proliferative response against anti-TcR monoclonal antibody stimulation. These results suggest that the thymus can induce extrathymic T cell differentiation through the influence of thymus-derived cytokine(s) including interleukin-7, and that such extrathymically differentiated T cells have acquired only a little or no ability for proliferation when they recognize antigen by their TcR.     

Contribution of alphabeta and gammadelta T cells to the generation of primary immunoglobulin G-driven autoimmune response in immunoglobulin- mu-deficient/lpr mice

Class switch recombination (CSR) is a T-cell-dependent mechanism regulating isotype switching in activated mature B cells. Recently we showed that T-cell-independent CSRs occur spontaneously during B lymphopoiesis, but such cells are negatively selected by Fas signalling. In immunoglobulin mu-deficient mice, lack of Fas rescues isotype-switched B cells, resulting in generation of an autoimmune primary immunoglobulin G (IgG) repertoire in muMT/lpr mice. In the present study, we studied the role of alphabeta and gammadelta T cells in regulating this primary gammaH-driven repertoire. We found that a lack of alphabeta T cells significantly inhibited IgG production and autoimmunity in muMT/lpr mice, whereas a lack of gammadelta T cells resulted in augmented IgG production and autoimmunity. Also, a lack of T cells in muMT mice rescued isotype-switched B cells and serum IgG, probably owing to the lack of available FasL. We suggest that although CSRs in B-cell lymphopoiesis are T-cell independent, alphabeta T cells are important in the expansion of isotype-switched B-cell precursors and in promoting gammaH-driven autoimmunity, whereas gammadelta T cells regulate these cells.