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.

An allogeneic microenvironment influences the phenotype of intermediate T-cell receptor cells expanding in MRL-lpr/lpr mice

MRL-lpr/lpr (lpr) mice fall victim to autoimmune disease owing to a lymphoproliferative disorder mainly of double-negative (DN) CD4- CD8- alpha beta T cells expressing a low density of interleukin-2 receptor beta-chain (IL-2R beta). It was previously revealed that the lpr gene is a defective Fas gene, into which an early transposon (ETn) of retrovirus is transfected. As a result of the failure of apoptosis, intermediate T-cell receptor (TCR) cells (i.e. TCRint cells) with DN phenotype abnormally accumulate in the periphery of lpr mice. We investigated herein how these TCRint cells are selected in terms of CD4, CD8 and TCR in lpr mice. When a whole fraction of mononuclear cells (MNC) in various immune organs of lpr mice was injected into scid mice (allogeneic circumstance), CD8+ TCRint cells mainly expanded. They had a high density of IL-2R beta. This was true when bone marrow cells of lpr mice were injected into scid mice. On the other hand, when MNC of the spleen and bone marrow in lpr mice were injected into irradiated (9 Gy) lpr mice (syngeneic circumstance), the major expanding cells were DN TCRint cells expressing a low density of IL-2R beta. A cell-sorting experiment for purified fractions demonstrated that only CD8- cells reconstituted TCRint cells in scid mice. Namely, DN CD4- CD8- cells as well as CD4+ cells which once acquired the mature phenotype, no longer switched their phenotype. These results suggest that the phenotype of TCRint cells is influenced by the surrounding microenvironment.

Intermediate TCR cells can induce graft-versus-host disease after allogeneic bone marrow transplantation

Mice fall victim to GVHD when subjected to immunosuppressive treatment and injected with allogeneic bone marrow cells. A major population of cells associated with GVHD is known to be T cells. However, whether such T cells are of thymic or extrathymic origin is obscure. We applied two immunosuppressive conditions, 9 and 6.5 Gy irradiation, to C3H/He mice (H-2k). Bone marrow cells for injection were obtained from C57BL/6 (B6) mice (H-2b). The 9-Gy mice were reconstituted by lymphocytes of donor origin and showed GVHD, whereas 6.5-Gy mice were reconstituted by lymphocytes of recipient origin and showed mild GVHD. The liver was the organ where the reconstitution of lymphocytes occurred efficiently, and a major lymphocyte subset was intermediate (int) CD3 cells (i.e., CD3int cells) in both mice. CD3int cells had the properties of extrathymic T cells, showing the phenotype of NK1.1 + CD3int using invariant V alpha 14 chain. In 6.5-Gy mice, allogeneic cells were rejected by extrathymic T cells of recipient origin. The stored CD3int cells from the liver of 9-Gy mice evoked similar GVHD when transferred into 6.5-Gy irradiated C3H/He mice. These results suggest that CD3int cells of extrathymic origin are a major population for the induction of GVHD under immunosuppressive conditions.

Circadian rhythm of leucocytes and lymphocytes subsets and its possible correlation with the function of the autonomic nervous system

There are physiological variations in the levels of leucocytes. Among these, the circadian rhythm is very important in terms of the magnitude. Since newly identified lymphocyte subsets (i.e. extrathymic T cells) have recently been detected, a comprehensive study of the circadian rhythm was conducted. All leucocytes were found to vary in number or proportion with a circadian rhythm and were classified into two groups. One group--granulocytes, macrophages, natural killer (NK) cells, extrathymic T cells, gammadelta T cells, and CD8+ subset--showed an increase in the daytime (i.e. daytime rhythm). The other group--T cells, B cells, alphabeta T cells, and CD4+ subset--showed an increase at night. Humans are active and show sympathetic nerve dominance in the daytime. Interestingly, granulocytes and lymphocyte subsets with the daytime rhythm were found to carry a high density of adrenergic receptors. On the other hand, lymphocyte subsets with the night rhythm carried a high proportion of cholinergic receptors. Reflecting this situation, exercise prominently increased the number of cells with the daytime rhythm. These results suggest that the levels of leucocytes may be under the regulation of the autonomic nervous system.

Neonatal granulocytosis is a postpartum event which is seen in the liver as well as in the blood

In a recent series of studies, we demonstrated that stress in humans and animals, with resultant sympathetic nerve strain, induces severe granulocytosis, because granulocytes carry adrenergic receptors on the surface. Because activated granulocytes produce free radicals and superoxides, they sometimes induce tissue damage if the stress is too strong or continuous. Human neonates are also known to show high levels of granulocytes in the peripheral blood. In this study, we investigated whether such neonatal granulocytosis are a stress-associated response at birth. Both human and mouse materials, before and after birth, were used. The number of leukocytes in the blood, as well as some other factors in the serum, were measured. Although levels of granulocytes were found to be low in fetal humans and mice, they increased sharply after birth. In parallel with this postpartal granulocytosis, transaminases in sera increased transiently. In reference to results of a transient elevation in the levels of catecholamines at birth in mice, all these phenomena resemble stress-associated responses. Indeed, fatty liver and hematopoietic destruction in the liver were also observed in mice and humans. At this time, the production of inducible nitric oxide synthase (iNOS) by granulocytes in the liver was evident. These results suggest that neonatal granulocytosis is a postpartum event which results from various stresses (e.g., oxygen stress) at birth. This event may be responsible for such well-known neonatal phenomena as the termination of fetal hematopoiesis in the liver and as neonatal jaundice.

Mouse liver T cells: their change with aging and in comparison with peripheral T cells

Mouse liver contains both IL-2Rbeta- (or low positive) high T-cell receptor (TCR(hi)) cells and IL-2Rbeta+ intermediate TCR (TCR(int)) cells. TCR(int) cells consist of natural killer 1.1 (NK1)+ and NK1- subsets. NK1- TCR(int) cells increase constantly with age whereas TCR(hi) cells decrease. NK1+ TCR(int) cell proportions in the liver increase until middle age and decrease thereafter. Although NK1+ TCR(int) cells in other organs are few regardless of age, NK1- TCR(int) cells gradually appear in other lymphoid organs with aging. Skewed usage of Vbeta7 and Vbeta8 TCR was observed in NK1+ TCR(int) cells in the liver but the predominance was less obvious in NK1- TCR(int) and TCR(hi) cells in the liver and other organs. TCR V alpha14 messenger RNA (mRNA) was detected in NK1+ TCR(int) cells but not in the other two populations. In contrast, although NK1+ TCR(int) cells contain virtually no V alpha11+ T cells, NK1- TCR(int) cells contain a much higher proportion (approximately 12%) of V alpha11+ T cells, whereas approximately 4% of TCR(hi) cells are V alpha11+. NK activities of liver mononuclear cells (MNC) and splenocytes decrease with aging, although the former is always greater than the latter. NK activity of liver MNC is a function of NK cells, partly NK1+ TCR(int) cells but not NK1- TCR(int) cells or TCR(hi) cells. These results suggest that lymphocytes of liver and other organs at old age are no longer occupied solely by conventional thymus-derived T cells, and the increase of extrathymic IL-2Rbeta+ NK1- TCR(int) cells in liver and periphery could be closely related to immunological changes with aging.

Autologous killing by a population of intermediate T-cell receptor cells and its NK1.1+ and NK1.1- subsets, using Fas ligand/Fas molecules

Self-reactive clones, estimated by anti-V beta monoclonal antibodies (mAb) in conjunction with the Mls system, are confined to a population of intermediate (int) T-cell receptor (TCR) (or CD3) cells (i.e. TCRint cells), but are not found among TCRhigh cells. The next questions to be answered are whether autologous killing is confined to TCRint cells and how such killing is mediated. In this study, 51Cr-labelled thymocytes of syngeneic or allogeneic origin were used as target cells (4-hr assay). When liver and splenic mononuclear cells (MNC) obtained from B6 mice were used as effector cells, prominent autologous killing was seen in liver MNC, but not splenic MNC. Such killing was not seen when thymocytes from B6-lpr/lpr mice (i.e. Fas-) were used as target cells, nor when liver MNC from MRL-gld/gld mice (i.e. Fas ligand-) were used as effector cells (target thymocytes of MRL(-)+/+ mice). Cell separation experiments using a cell sorter revealed that autologous killing was mediated for the most part by CD3int cells, while allogeneic killing was mediated entirely by natural killer (NK) cells, TCRint cells and TCRhigh cells. Among CD3int cells, the NK1.1+ subset (i.e. NK1.1+ T cells) manifested a higher level of autologous killing than did the NK1.1- subset. Consistent with the results of a functional assay, it was found by reverse-transcription-polymerase chain reaction (RT-PCR) assay that CD3int cells among liver MNC showed the expression of Fas ligand mRNA, while thymocytes expressed Fas mRNA. When class I major histocompatibility complex (MHC)- thymocytes (from beta 2-microglobulin-deficient mice) were used as target cells, NK cells, but not CD3int cells, showed potent cytotoxicity. These results suggest that autologous killing is a major function of TCRint cells with self-reactivity, and that such killing is mediated by means of Fas ligand/Fas molecules.

Self-reactive forbidden clones are confined to pathways of intermediate T-cell receptor cell differentiation even under immunosuppressive conditions

It is believed that self-reactive forbidden T-cell clones are generated by 'failure' of the pathway of T-cell differentiation in the thymus, if it is disturbed. We examined how such forbidden clones are generated under immunosuppressive conditions. Mice were treated with an injection of deoxyspergualin, FK506, or cycloporin A. From day 3, the number of cells yielded by various organs decreased. Because of the resistance of intermediate (int) T-cell receptor (TCR) cells (i.e. TCRint cells), they became more prominent in proportion than TCRhigh cells. TCRhigh cells are conventional T cells generated through the mainstream in the thymus, whereas TCRint cells are primordial T cells generated by the extrathymic pathway or an alternative intrathymic pathway. Similar to untreated mice, forbidden V beta 3+ and V beta 11+ clones in C3H/He (Mls-1b2a) mice were confined to TCRint cells after treatment; there was no leakage of forbidden clones into TCRhigh cells in the thymus and periphery. In parallel with the increase in the proportion of TCRint cells, the proportion of forbidden clones also increased under immunosuppressive states, especially in the liver. Liver mononuclear cells isolated from treated mice still had the potential to mediate autologous killing. The present results suggest that the generation of self-reactive clones is highly restricted to the pathways of TCRint cell differentiation even under immunosuppressive conditions.

Absolute dependence of T cell receptor(hi) cell generation and relative dependence of T cell receptor(int) cell generation on the thymus

Recent evidence indicates that conventional T cells are generated by the mainstream of T cell differentiation in the thymus and acquire a high density of T cell receptor expression (i.e. TCRhi). In contrast, primordial T cells (or NK1.1+ T cells) are generated by the extrathymic pathways or an alternative intrathymic pathway and express an intermediate density of TCR (i.e. TCRint). To obtain further evidence, it was examined how thymus grafting influenced the distribution of T cell populations in athymic nude mice. When BALB/c nu/nu mice were engrafted with thymocyte-depleted BALB/c+/+ fetal thymi, two changes emerged after grafting: nude mice generated TCRhi cells de novo in the periphery as well as in the grafted thymi, and the absolute number of interleukin-2 receptor beta chain+ TCRint cells increased prominently in number in the periphery. Among thymic hormones tested, the administration of thymosin alpha induced a slight expansion of CD3int cells in nude mice. To examine a possible interaction of TCRint cells with TCRhi cells in the periphery, B6 nu/nu mice (Ly5.2+) were injected with TCRhi cells purified from the spleen of B6 Ly5.1 congenic mice. In this case, TCRint (Ly5.2+) cells expanded well in all tested organs of nude mice. These results suggest that the generation of TCRhi cells is absolutely dependent on the thymus and that TCRint cells expand under the influence of the thymus (humoral) and due to interaction with thymus-derived conventional T 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.

Cytotoxic activity against tumour cells mediated by intermediate TCR cells in the liver and spleen

Morphological and phenotypic characterization in previous studies has indicated that intermediate (int) T-cell receptor (TCR) cells or T natural killer (TNK) cells may stand at an intermediate position between NK cells and high TCR cells of thymic origin in phylogenetic development. In this study, a functional study on cytotoxic activity against various tumour targets was performed in each purified subset. When a negative selection method entailing in vivo injection of anti-asialo GM, antibody or anti-interleukin (IL)-2R beta monoclonal antibody (mAb) was applied, IL-2R beta 1 CD3 NK cells were found to have the highest NK activity while IL-2R beta 1 int CD3 (or TCR) cells had a lower level of the NK activity. High CD3 cells (freshly isolated) did not have any such activity. Sorting experiments further revealed that the NK function mediated by int CD3 cells was augmented when they were exposed to anti-CD3 mAb. anti-TCR alpha beta, or anti-TCR-delta mAb. This phenomenon was not observed in NK cells and high CD3 cells. More importantly, when anti-CD3 mAb (or anti-TCR mAb) was added to the assay culture, int CD3 cells became cytotoxic against even NK-resistant tumour (Fc gamma R-. Fas+) targets. Liver mononuclear cells or int CD3 cells exposed to anti-CD3 mAb for 6 hr showed an elevated level of perforin in their cytoplasms. The present results suggest that int CD3 cells are usually non-cytotoxic against various tumours but become functional after being stimulated via the TCR CD3 complex.

Supportive cellular elements for hepatic T cell differentiation: T cells expressing intermediate levels of the T cell receptor are cytotoxic against syngeneic hepatoma, and are lost after hepatocyte damage

Extrathymic T cells exist in the liver and are often seen in close contact with Kupffer cells in the hepatic sinusoids. Since selective depletion of Kupffer cells has become possible by using liposome-encapsulated clodronate, it was investigated whether elimination of Kupffer cells influences the level of extrathymic T cells in the liver. Extrathymic T cells were identified as interleukin-2 receptor beta-chain (IL-2R beta) intermediate TCR (TCRint) cells by two-color staining for CD3 or T cell receptor (TCR) and IL-2R beta. The elimination of Kupffer cells did not significantly affect levels of TCRint cells up to 7 days after treatment. We then examined monocyte colony stimulating factor (M-CSF)-deficient op/op mice (low levels of Kupffer cells). Extrathymic T cells both in the liver and spleen of these mice were detected at a level comparable to that of control mice. Since extrathymic T cells in the liver are sometimes located in the parenchymal space, the relationship between extrathymic T cells and hepatocytes was then examined. Electron microscopy revealed that some hepatic T cells adhered directly to hepatocytes. When hepatocytes were damaged by a single injection of CCl4, hepatocyte death and subsequent hepatic fibrosis were induced. Beginning 3 days after injection, CD3int cells, but not other type of cells, decreased prominently. Purified CD3int cells, as well as whole lymphocytes in the liver, were cytotoxic against syngeneic hepatoma. In parallel with the above-mentioned hepatic damage, the cytotoxic activity of lymphocytes against such targets was impaired in the liver. These results suggest that extra-thymic generation of TCRint cells and their acquisition of cytotoxic function are relatively independent of Kupffer cells, but are dependent on hepatocytes.

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.

Extrathymic T cells stand at an intermediate phylogenetic position between natural killer cells and thymus-derived T cells

A series of recent studies have revealed that extrathymic pathways of T cell differentiation exist at multiple sites in mice and humans. In terms of their properties, extrathymic T cells may stand at an intermediate position between natural killer (NK) cells and thymus-derived T cells in phylogenetic development. It is speculated that primitive lymphocytes such as NK cells and extrathymic T cells develop from primordial macrophages in intraepithelial regions of e.g., the intestine, skin and liver. In this regard, the immune system of the bone marrow and thymus is relatively recent, developing after the emergence of living beings onto the land (i.e., amphibia). A complete elimination of self-reactive T cell clones occurs in mainstream intrathymic T cell differentiation and a consistent generation of such clones occurs through the extrathymic pathways. Therefore, thymus-derived T cells are efficient for processing foreign antigens, whereas extrathymic T cells recognize abnormal self-cells. Although thymus-derived T cells play the major role in youth, extrathymic T cells may play rather a pivotal role with aging and under conditions of malignancy, intracellular infections, pregnancy, and autoimmune diseases.