Radioresistance of intermediate TCR cells and their localization in the body of mice revealed by irradiation

Depletion of NK Cells Resistant to Ionizing Radiation Increases Mutations in Mice After Whole-body Irradiation

BACKGROUND

Ionizing radiation is a very powerful genetic mutagenic agent. Although immune cells are very sensitive to radiation, their sensitivity varies between different types of immune cell. We hypothesized that radiation-resistant immune cells survive after irradiation and then play a role in removing mutant cells.

MATERIALS AND METHODS

Splenic lymphocytes and mice were irradiated with γ-rays. Cell populations were analyzed using flow cytometry after dyeing with antibodies and expression of B-cell lymphoma 2 (BCL2) was measured by western blot analysis. To deplete natural killer (NK) cells, anti-asialo GM1 antiserum was used. Micronuclei in polychromatic erythrocytes were measured by May-Grunwald/Giemsa staining. H-2Kb loss variant in T-cells induced by irradiation of B6C3F1 mice were detected by flow cytometry.

RESULTS

When splenic lymphocytes were irradiated in vitro, B cells notably died, while NK cells did not. In vivo, on the third day after whole-body irradiation, the total number of lymphocytes in the spleen decreased rapidly, but the proportion of NK cells was approximately three times higher than that of the normal control group. In addition, it was confirmed that high expression of BCL2 in NK cells was maintained after irradiation, whereas that of B-cells was not. Removal of NK cells by injection with anti-asialo GM1 antiserum immediately after irradiation increased the micronuclei of polychromatic erythrocytes in the bone marrow and the variant fraction with H-2kb loss in the spleen.

CONCLUSION

These results provide important evidence that radioresistant NK cells apparently survive by escaping apoptosis in the early stages after irradiation, and work to eliminate mutant cells resulting from γ-ray irradiation. Future studies are needed to reveal why NK cells are resistant to radiation and the in-depth mechanisms involved in the elimination of radiation-induced mutant cells.

The NK1.1+T cells alive in irradiated mice play an important role in a Th1/Th2 balance

PURPOSE

Ionizing radiation is known to reduce the helper T (Th) 1 like function, resulting in a Th1/Th2 imbalance. We studied whether NK1.1+T cells which were the most resistant against gamma-irradiation impact on the imbalanced immune response after irradiation.

MATERIALS AND METHODS

C57BL/6 mice received a whole-body gamma-irradiation (WBI) of 4 Gy. The primary T cells were separated by magnetic cell sorter (MACS) using the anti-CD90.2 antibody. The apoptotic cells were detected by propidium iodide (PI) staining. To determine the Th1 and Th2 cell functions, the production of interferon (IFN)-gamma and interleukin (IL)-4 were analysed by a reverse transcriptase-polymerase chain reaction (RT-PCR) and an enzyme linked immunosorbent assay (ELISA). NK1.1+T cells were detected by flow cytometry. For depletion of the NK1.1+T cells in the WBI mice, anti-asialo GM1 antiserum was injected.

RESULTS

The CD90.2 positive cells of the WBI mice produced significantly more Th2 type cytokines and also produced Th1 type cytokines at a not lower level than normal mice, and contained a higher absolute number of NK1.1+T cells. Also, the proportion of the NK1.1+T cells increased in the WBI mice. We found that the NK1.1+T cells were resistant to radiation-induced apoptosis in comparison with the conventional T cells. The depletion of NK1.1+T cells in WBI mice resulted in higher production of IgE and IL-4 and lower secretion of IL-12p70.

CONCLUSION

Our findings revealed that NK1.1+T cells that survive at an early stage after irradiation play an important role in the balance of the immune responses at a late stage after irradiation.

Down-regulation of the invariant Valpha14 antigen receptor in NKT cells upon activation

NKT cells expressing the invariant Valpha14 antigen receptor constitute a novel lymphocyte subpopulation with immunoregulatory functions. Stimulation via their invariant Valpha14 receptor with anti-CD3 or a ligand, alpha-galactosylceramide (alpha-GalCer), triggers activation of Valpha14 NKT cells, resulting in a rapid cytokine production such as IFN-gamma and IL-4. Soon after their receptor activation, Valpha14 NKT cells disappeared as judged by staining with CD1d tetramer loaded with alpha-GalCer (alpha-GalCer/CD1d tetramer), which has been believed to be due to apoptotic cell death. Here we show that such a disappearance was largely attributed to down-regulation of the Valpha14 receptor. In fact, Valpha14 NKT cells were relatively resistant to apoptosis compared to the conventional T cells as evidenced by less staining with Annexin-V, a limited DNA fragmentation, and their preferential expression of anti-apoptotic genes such as NAIP and MyD118. Furthermore, they did not become tolerant, and maintained their proliferative capacity and cytokine production even after their receptor down-regulation. These as yet unrecognized facets of Valpha14 NKT cells are discussed in relation to their regulatory functions.

Requirements for developing mixed-chimerism in nonmyeloablative total-lymphoid irradiated mice: role of IL-4 and immunoredirection

BACKGROUND

Adult mice treated with total-lymphoid irradiation (TLI) followed by hematopoietic cell transfer develop stable mixed-chimerism. The purpose of the study is to examine the requirements for the development of mixed-chimerism and characterize the immune responses associated with mixed-chimerism.

METHODS

T-cell number and function were examined in spleens of TLI-treated mice at various times after the completion of TLI by fluorescence-activated cell sorter (FACS) analysis and enzyme-linked immunosorbent assay (ELISA). TLI-treated BALB/c mice were injected with CAF(1) spleen cells between 2 and 28 days after completing TLI, with or without concurrent anti-IL-4. The extent of mixed-chimerism was determined using multiparameter FACS analysis. Enzyme-linked immunosorbent spot (ELISPOT) assays were used to measure anti-donor CD4+ and CD8+ immune responses.

RESULTS

TLI treatment results in transient lymphopenia, sparing CD4 cells relative to CD8 cells, followed by gradual, partial recovery over 28 days. Day 2 post-TLI T cells produce more interleukin (IL)-4, but less IL-2, interferon (IFN)-gamma and IL-10, while day 28 post-TLI T cells produce more IFN-gamma relative to IL-4. More than 70% of mice develop mixed-chimerism when injected with CAF(1) cells at 2 days post-TLI, while none become chimeric if injected at 28 days post-TLI. Mixed-chimeric mice contain more anti-donor Th2 CD4 cells and less anti-donor TC1 CD8 cells compared with nonchimeric mice and nonirradiated controls. Treatment with anti-IL-4 inhibits the development of mixed-chimerism ( <0.05), and these nonchimeric mice contain donor-reactive TC1 CD8 cells.

CONCLUSIONS

IL-4 plays a role in the development of mixed-chimerism, perhaps by inhibition of anti-donor TC1 CD8 cells or enhancement of anti-donor Th2 CD4 cells.

Size of the population of CD4+ natural killer T cells in the liver is maintained without supply by the thymus during adult life

Given that there are few natural killer T (NKT) cells in the liver of athymic nude mice and in neonatally thymectomized mice, it is still controversial whether all NKT cells existing in the liver are supplied by the thymus or if some such cells develop in the liver. To determine whether or not NKT cells are consistently supplied from the thymus during adult life, thymectomy was conducted in mice at the age of 8 weeks. Interestingly, the proportion and number of CD4+ NKT cells increased or remained unchanged in the liver after adult thymectomy and this phenomenon continued for up to 6 months after thymectomy. The administration of alpha-galactosylceramide induced severe cytopenia (due to apoptosis) of CD4+ NKT cells in the liver on day 1, but subsequent expansion of these NKT cells occurred in thymectomized mice similar to the case in normal mice. However, in thymectomized mice given lethal irradiation (9.5 Gy) and subsequent bone marrow transfer, the population of CD4+ NKT cells no longer expanded in the liver, although that of CD8+ NKT cells did. These results suggest that thymic CD4+ NKT cells, or their progenitors, may migrate to the liver at a neonatal stage but are not supplied from the thymus in the adult stage under usual conditions. CD8+ NKT cells can be generated in the liver.

Extrathymic pathways of T-cell differentiation and immunomodulation

It is well established that the thymus is an essential organ for the support of T-cell differentiation. However, some T cells, termed extrathymic T cells, have been found to differentiate without such support by the thymus. The major sites of these T cells are the intestine and liver. Subsequent studies have revealed that extrathymic T cells are also present in the uterus and exocrine glands (e.g., the salivary gland). Depending on the sites, extrathymic T cells have some distinct properties as well as some common properties. For example, all extrathymic T cells have a TCR-CD3 complex similar to thymus-derived T cells. Extrathymic T cells comprise both alpha beta T cells and gamma delta T cells. Although extrathymic T cells are very few in number at any extrathymic sites in youth, they increase in number as a function of age. This phenomenon seems to occur in parallel with thymic involution. Even in youth, extrathymic T cells are activated in number and function by stress, in autoimmune diseases, and during pregnancy. Acute thymic atrophy always accompanies this activation. Therefore, reciprocal regulation between extrathymic T cells and thymus-derived T cells might be present. We hypothesize that extrathymic T cells are intimately associated with innate immunity and that the mechanisms underlying autoimmune diseases and intracellular infection (e.g., malaria) cannot be properly understood without introducing the concept of extrathymic T cells.

CD4(+) Valpha14 natural killer T cells are essential for acceptance of rat islet xenografts in mice

Pancreatic islet transplantation represents a potential treatment for insulin-dependent diabetes mellitus. However, the precise cellular and molecular mechanisms of the immune reactions against allogeneic and xenogeneic transplanted islets remain unclear. Here, we demonstrate that CD4(+) Valpha14 natural killer T (NKT) cells, a recently identified lymphoid cell lineage, are required for the acceptance of intrahepatic rat islet xenografts. An anti-CD4 mAb, administrated after transplantation, allowed islet xenografts to be accepted by C57BL/6 mice, with no need for immunosuppressive drugs. The dose of anti-CD4 mAb was critical, and the beneficial effect appeared to be associated with the reappearance of CD4(+) NKT cells at around 14 days after transplantation. Interestingly, rat islet xenografts were rejected, despite the anti-CD4 mAb treatment, in Valpha14 NKT cell-deficient mice, which exhibit the normal complement of conventional lymphoid cells; adoptive transfer of Valpha14 NKT cells into Valpha14 NKT cell-deficient mice restored the acceptance of rat islet xenografts. In addition, rat islet xenografts were accepted by Valpha14 NKT mice having only Valpha14 NKT cells and no other lymphoid cells. These results indicate that Valpha14 NKT cells play a crucial role in the acceptance of rat islet xenografts in mice treated with anti-CD4 antibody, probably by serving as immunosuppressive regulatory cells.

Resistance of extrathymic T cells to stress and the role of endogenous glucocorticoids in stress associated immunosuppression

When mice were exposed to restraint stress for 12 or 24 h, severe lymphopenia was induced in all immune system organs, including the liver and the thymus. However, in adrenalectomized mice, this response was completely absent. Phenotypic characterization revealed that interleukin (IL)-2Rbeta+CD3int cells (i.e. extrathymic T cells) with CD4+ phenotype and the NK1.1+ subset of CD3int cells (i.e. NKT cells) in the liver as well as the mature conventional T cells in the thymus were resistant to such stress. In adrenalectomized mice, there was no significant change in the distribution of lymphocyte subsets in all tested organs before stress. Interestingly, the number of lymphocytes in the liver and spleen and the proportion of NKT cells in the liver rather increased after stress in these adrenalectomized mice. Therefore, endogenous steroid hormones were indicated to be important in the induction of immunosuppressive states after stress. Among stress associated cytokines, the secretion of tumour necrosis factor (TNF)-alpha was completely suppressed while that of IL-6 was partially suppressed in adrenalectomized mice. These results suggest that endogenous steroid hormones are important for the induction of the stress associated immunosuppression and that NKT cells are resistant to stress, namely, resistant to exposure to endogenous steroid hormones.

Participation of NK1.1+ T cells in the rejection of lpr alphabetaT cells when bone marrow cells of lpr mice are transplanted into B6 mice

When C57BL/6 (B6) mice were irradiated (9 Gy) and received bone marrow (BM) cells of B6-lpr/lpr mouse origin (i.e., lpr-->B6), all mice died within 6 days. In the irradiated B6 mice, radioresistant CD3 IL-2Rbeta+ NK cells and IL-2Rbeta+ CD3int cells (i.e., CD3int cells of extrathymic origin) remained, especially in the liver. There were two subsets, NK1.1+ and NK1.1-, among the IL-2Rbeta+ CD3int cells. However, the NK1.1+ subset (i.e., NK1.1- T cells) was much more radioresistant, and the majority of CD3int cells belonged to this subset in irradiated mice. The expansion of lymphocytes from injected BM cells did not occur in the irradiated B6 mice. However, such expansion did take place in irradiated B6-lpr/lpr mice injected with both BM cells of B6-lpr/lpr and B6 origin. As a result, the mice subjected to BM cells survived. Irradiated B6 mice were treated in vivo with anti-NK1.1 mAb or anti-asialoGM1 antibody to eliminate NK cells alone or both NK cells and NK1.1+ T cells. When irradiated B6 mice were pretreated with anti-NK1.1 mAb, the mice could survive. These results suggest that intact NK1.1+ T cells of extrathymic origin may recognize abnormal BM cells with the lpr gene and inhibit the expansion of lymphocytes, including abnormal double-negative CD4 8 cells, in B6-lpr/lpr mice. To inhibit the expansion of lymphocytes, mechanisms other than Fas ligand/Fas molecules on extrathymic T cells may be responsible.

IL-4-Producing NK1.1+ T Cells Are Resistant to Glucocorticoid-Induced Apoptosis: Implications for the Th1/Th2 Balance

To elucidate the mechanisms by which glucocorticoids promote Th2-type responses, we investigated the influence of dexamethasone (DEX) on both cytokine production and viability of NK1.1+ T cells. The in vivo administration of DEX enhanced the IL-4 production of spleen cells and liver mononuclear cells in wild-type mice, but not in β2m-deficient mice. DEX reduced the cellularity of conventional T cells, but not that of NK1.1+ T cells, in both spleen and liver, suggesting an increased proportion of NK1.1+ T cells. Moreover, the proportion of IL-4-producing NK1.1+ T cells increased in the DEX-injected mice. These results suggest that DEX induced IL-4 production through the preferential survival of IL-4-producing NK1.1+ T cells. In investigating the reason for the preferential survival of NK1.1+ T cells, we found that NK1.1+ T cells were resistant to DEX-induced apoptosis and expressed a higher level of intracellular Bcl-2 compared with conventional NK1.1− T cells. In addition, splenic and hepatic NK1.1+ T cells were resistant to radiation-induced apoptosis. Collectively, our findings revealed an important role for NK1.1+ T cells in the regulation of Th1/Th2 balance by glucocorticoids and their possible functions under various apoptotic stimuli.

Phenotypic and functional modulation of T cells in vivo by extrathymic T cells when T cells with MHC class II disparity were injected into athymic nude mice

TCRhigh cells are generated by the mainstream of T cell differentiation in the thymus, whereas TCRint cells (or NK1.1+ T cells) are generated extrathymically in the liver and by an alternative intrathymic pathway. It is still unknown how these T cell populations interact in vivo with each other. To investigate the interaction of TCRint cells with TCRhigh cells, we used congenitally athymic nude (B6-nu/nu) mice which carry only TCRint cells in all immune organs. When TCRhigh cells from B6-C-H-2bm12 (bm12) mice (i.e. I-Abm12) were injected into B6-nu/nu mice (i.e. 1-Ab), the expanding T cell population was a mixture of TCRhigh cells of donor origin and TCRint cells of recipient origin. However, 9 Gy-irradiated nude mice permitted a full expansion of TCRhigh cells which expressed the IL-2Ralpha+beta+ phenotype, namely, they were at the most activated state. These mice died of acute graft-versus-host disease (GVHD) within 5 days. On the other hand, non-irradiated nude mice suppressed the expansion of TCRhigh cells of donor origin and such TCRhigh cells continued to have the IL-2Ralpha(+/-)beta+ phenotype. These mice could survive but showed signs of chronic GVHD thereafter. In both situations, CD4+alphabeta T cells expanded irrespective of donor or recipient origin. These results suggest that TCRint cells in the recipient mice possess a regulatory function in relation to donor TCRhigh cells; as a result, fully activated TCRhigh cells acquired the IL-2Ralpha+beta+ phenotype and injured the host, but TCRhigh cells suppressed in vivo remained as the IL-2Ralpha(+/-)beta+ phenotype and only partially injured the host.

The impact of psychological stress on the efficacy of anti-viral adoptive immunotherapy in an immunocompromised host

Adoptive immunotherapy represents a potentially effective approach by which to control the extent of viral infections in an immunocompromised host. However, the impact of psychological stress and its associated neuroendocrine components on the efficacy of such a treatment strategy has yet to be determined. In the studies described herein, we have developed and utilized a model of primary, local herpes simplex virus (HSV) infection in radiation-induced, immunosuppressed C57BL/6 mice to investigate the role of stress in altering the protective capacity of adoptively transferred lymphocytes that contribute to the resolution of primary HSV infection. The sublethal dose of irradiation chosen for this model was shown to abrogate the local, adaptive immune response to HSV infection as measured by the degree of in vivo lymphoproliferation, development of HSV-specific cytotoxic T lymphocytes (CTL), and production of gamma interferon (IFN-gamma). Both short- and long-term acute stress, applied in the form of physical restraint, diminished the effectiveness of adoptively transferred lymphocytes as was indicated by an enhancement of viral replication in the footpad tissue and an increased rate of mortality. A reduction in the levels of IFN-gamma at the site of primary HSV infection represented at least one mechanism underlying this suppression of anti-viral immunity. Furthermore, the time-dependent restoration of immune function following irradiation was shown to be compromised in mice subjected to the restraint stress procedure. Together, these findings emphasize the potential role of psychological stress in suppressing both the capability of adoptive immunotherapeutic procedures to combat viral infection and the reestablishment of immune function in individuals who have undergone immunosuppressive therapy.

Mouse CD1-specific NK1 T cells: development, specificity, and function

NK1 T cells are a specialized population of alpha/beta T cells that coexpress receptors of the NK lineage and have the unique potential to very rapidly secrete large amounts of cytokines, providing early help for effector cells and regulating the Th1 or Th2 differentiation of some immune responses. NK1 T cells express a restricted TCR repertoire made of an invariant TCR alpha chain, V alpha 14-J alpha 281, associated with polyclonal V beta 8, V beta 7, and V beta 2 TCR beta chains. NK1 T cells recognize the products of the conserved family of MHC class I-like CD1 genes, apparently in the absence of foreign antigens. Thus, this novel regulatory pathway, which straddles the innate and the adaptive immune systems, is unique in that its activation may not require associative recognition of antigen. Here, we review the specificity and function of mouse NK1 T cells, and we discuss the relationship of this lineage to mainstream T cells and NK cells.

Restricted appearance of self-reactive clones into T cell receptor intermediate cells in neonatally thymectomized mice with autoimmune disease

Neonatally thymectomized (NTx) mice fall victim to such autoimmune diseases as gastritis and pancreatitis with aging. Self-reactive T cell clones are known to be consistently generated through TCR intermediate (i.e. TCRint) cell differentiation in normal mice (i.e. via the extrathymic pathways and an alternative intrathymic pathway). It was investigated whether the generation of such clones in NTx mice follows this rule or whether they are generated by default via mainstream T cell differentiation in the thymus. The majority of T cells generated in NTx mice were TCRint cells in all organs tested. In contrast to athymic mice, which carry only TCRint cells with aging, a leaky appearance of high TCR (i.e. TCRhi) cells emerged in the lymph nodes and other organs of NTx mice. Self-reactive clones estimated by anti-Vbeta monoclonal antibodies in conjunction with the Mls system were confined to TCRint cells in all tested organs, including a target organ, the stomach, in NTx mice. A leaky population of TCRhi cells did not contain a significant number of self-reactive clones. Moreover, such self-reactive clones among TCRint cells in NTx mice with autoimmune disease were shown to be nonanergic in the proliferation assay. The present results suggest that the generation of self-reactive clones is totally due to TCRint cell differentiation, although it is still undetermined whether the expanding TCRint cell population is generated via the extrathymic pathway or an alternative intrathymic pathway. It is shown here not to be due to a failure of the TCRhi cell-differentiation pathway in NTx mice.

Interleukin-12 induces cytotoxic NK1+ alpha beta T cells in the lungs of euthymic and athymic mice

We recently reported that interleukin-12 (IL-12) stimulated hepatic NK1.1 Ag+ alpha beta T cells with intermediate T-cell receptor (TCR; NK1+ TCRint cells) and enhanced their NK1 expression (NK1high TCRint), and that these cells acquire strong major histocompatibility complex (MHC) unrestricted cytotoxicity in C57BL/6 mice, both +/+ and nu/nu. In the present study, we find that although murine lung normally has few NK1+ TCRint cells, NK1high TCRint cells are induced in+/+ and nu/nu mice after systemic administration of IL-12; these cells exhibit strong MHC unrestricted cytotoxicity against NK-sensitive and -resistant targets. A small number of NK1high TCRint cells was also found in peripheral blood after increased amounts of IL-12 were administered. Cytotoxicity tests in vitro revealed that the cytotoxic activity of the lung mononuclear cells (MNC) of C57BL/6 mice induced by IL-12 was abrogated by the depletion of either NK1+ or CD3+ cells, but not of CD8+ cells, as reportedly was the case of hepatic MNC, suggesting that NK1high TCRint cells are an antimetastatic population not only in the liver but also in the lung of mice. IL-12 injection into mice markedly elevates serum interferon-gamma (IFN-gamma) levels. However, although IL-12-induced cytotoxicity of NK1high TCRint cells was significantly reduced by anti-IFN-gamma antibody injection (which decreased serum IFN-gamma to an undetectable level), the appearance of NK1high TCRint cells in the lung and liver was not so affected. These results suggest that IFN-gamma is an important mediator of the cytotoxicity of NK1high TCRint cells but is not an essential factor for induction of these cells. We also added data showing that IL-12 has a broad antimetastatic effect against various liver and lung metastatic tumours intravenously injected into several strains of mice, including NK-deficient bg/bg mice. It can be considered that, in addition to NK cells, CD8+ cytotoxic T cells and gamma delta T cells, NK1+ TCRint cells can be categorized as one of the cytotoxic effector populations. These novel type cells distinct from regular T cells may play an important role in monitoring intra- and perivascular areas.

Origin of CD57+ T cells which increase at tumour sites in patients with colorectal cancer

Human T cells carrying natural killer (NK) markers, CD57 or CD56 antigens, appear to be distinguishable from other T cell subsets in terms of their granular lymphocyte morphology and their numerical increase in patients with AIDS and in recipients of bone marrow transplantation. At the beginning of this study, we observed that CD57+ T cells as well as CD56+ T cells were abundant at tumour sites in many patients with colorectal cancer. Since all these findings for CD57+ T cells are quite similar to those of extrathymic T cells seen in mice, we investigated how CD57+ T cells are distributed to various immune organs in humans. They were found to be present mainly in the bone marrow and liver, but to be completely absent in the thymus. Similar to the case of extrathymic T cells in mice, they were observed to consist of double-negative CD4-8- subsets as well as single-positive subsets (preponderance of CD8+ cells), and to contain a considerable proportion of gamma delta T cells. These features are striking when compared with those of CD57- T cells, which are characterized by an abundance of CD4+ subsets and alpha beta T cells. Not only at tumour sites but also in the peripheral blood, some patients with colorectal cancer displayed elevated levels of CD57+ cells. These results suggest that CD57+ T cells may be of extrathymic origin, possibly originating in the bone marrow and liver, and may be associated with tumour immunity, similar to another extrathymic population of CD56+ T cells in humans.

Self-reactive T cell clones in a restricted population of interleukin-2 receptor beta+ cells expressing intermediate levels of the T cell receptor in the liver and other immune organs

T cells expressing high levels of the T cell receptor (TCRhigh) differentiate in the major intrathymic pathway and then distribute to the peripheral immune organs, whereas T cells expressing intermediate levels of the TCR (TCRint) differentiate in both extrathymic pathways and an alternative intrathymic pathway and localize in unique sites, including the liver and thymic medulla. Since TCRint cells constitutively express interleukin-2 receptor beta-chain (IL-2R beta), two-color staining for CD3 (or TCR) and IL-2R beta clearly distinguished IL-2R beta+ CD3int (or TCRint) cells from IL-2R beta-, CD3high cells. CD3int cells may be considered to be primordial T cells based on their phenotype, morphology and other functional properties. In this study, using anti-V beta mAb in conjunction with the endogenous superantigen Mls, the distribution of self-reactive clones among T cells generated in all of the above pathways was investigated in mice. Self-reactive T cell clones were confined to IL-2R beta+, CD3int cells, in all of the organs tested. A significant proportion of self-reactive clones was never identified among CD3high cells in the thymus and peripheral immune organs in either young (8 week old) or old (50 week old) mice. Possibly reflecting their self-reactivity, CD3int cells, but neither NK cells nor CD3high cells had a potent cytotoxic effect against a syngeneic hepatoma in the presence of anti-CD3 mAb. These results raise the possibility that CD3int cells seen in the liver and thymus might belong to a similar primordial lineage of T cells, and that self-reactive clones are not generated through the major intrathymic pathway, but only through extrathymic pathways and an alternative intrathymic pathway.

Androgen regulation of intra-and extra-thymic T cells and its effect on sex differences in the immune system

Male predominance of malignant disease and female predominance of autoimmune diseases is widely known in humans. To elucidate one of the underlying mechanisms, we examined whether sex differences exist at the level of extra-thymic T cells in various organs of mice under physiological conditions. Effects of castration and testosterone administration were also examined. Intra- and extra-thymic T cells with T cell receptors (TCR) of bright and intermediate intensities, respectively, and with nil and high levels of the interleukin-2 receptor beta-chain respectively, were identified by immunofluorescence. Of the three strains tested, it was demonstrated that intermediate TCR cells were predominant in the liver of female mice. In the liver of male mice after bilateral orchidectomy, mononuclear cells increased and intermediate TCR cells predominated as if they were female; testosterone treatment prevented this immunological consequence of orchidectomy. As extra-thymic T cells comprise a considerable proportion of self-reactive forbidden clones and possess cytotoxic activity against syngeneic tumour cells, the present results suggest a possible relationship between (a) physiologically low levels of extra-thymic T cells in males and the male predominance of malignancy, and (b) the high levels of extra-thymic T cells in females and female predominance of autoimmune diseases.

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 beta-chain (IL-2R beta), whereas those in the intestine, especially intraepithelial lymphocytes, have TCR of bright intensity, consisting of a mixture of IL-2R beta+ and IL-2R beta-. All mature thymocytes and thymus-derived T cells seen in the peripheral immune organs are TCR-bright+ IL-2R beta- 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.

Female predominance of extrathymic T cells in mice: statistical analysis

Female predominance of autoimmune diseases is widely known in humans and animals. To elucidate one of the underlying mechanisms, we examined whether sex differences exist at the level of extrathymic T cells in various organs of mice under physiological conditions. This attempt came from previous experimental results showing that estrogen administration to mice activates extrathymic T cells in the liver. Extrathymic T cells expressing TCR (and CD3) of intermediate intensity (i.e., intermediate TCR cells) and a high level of IL-2 receptor beta-chain (IL-2R beta), and thymus-derived T cells expressing TCR of bright intensity (i.e., bright TCR cells) and lacking IL-2R beta, were identified by immunofluorescent tests using mAbs. Three groups of different strains were examined. It was demonstrated that intermediate TCR cells were much more predominant in the liver and some other organs tested of female mice than of male mice, of each strain tested.