Existence of a small population of IL-2R beta hi TCRint cells in SCG and MRL-lpr/lpr mice which produce normal Fas mRNA and Fas molecules from the lpr gene

Immunologic states of autoimmune diseases

The etiology and immunologic states of autoimmune diseases have mainly been discussed without consideration of extrathymic T cells, which exist in the liver, intestine, and excretion glands. Because extrathymic T cells are autoreactive and are often simultaneously activated along with autoantibody-producing B-1 cells, these extrathymic T cells and B-1 cells should be introduced when considering the immunologic states of autoimmune diseases. The immunologic states of autoimmune diseases resemble those of aging, chronic GVH disease, and malarial infection. Namely, under all these conditions, conventional T and B cells are rather suppressed concomitant with thymic atrophy or involution. In contrast, extrathymic T cells and B-1 cells are inversely activated at this time. These facts suggest that the immunologic states of autoimmune diseases should be reevaluated by introducing the concept of extrathymic T cells and autoantibody-producing B-1 cells, which might be primordial lymphocytes in phylogeny.

Multipotential acceptance of Peyer's patches in the intestine for both thymus-derived T cells and extrathymic T cells in mice

Peyer's patches (PP) are important inductive sites for the mucosal immune response. It is well known that lymphocytes that migrate into PP are mainly of T-cell lineage from thymus-derived cells (i.e. alphabetaTCR(high) cells). In this study, we further characterized the properties of PP lymphocytes in mice using a mouse model of colitis induced by dextran sulphate sodium (DSS). Although the major site of the inflammation induced by DSS is known to be the large intestine, the small intestine was also damaged. When mice developed DSS-induced colitis, CD3+CD8+B220+ gammadelta T cells increased in PP in the small intestine. These gammadelta T cells, which are not seen in the PP of normal mice, resembled intraepithelial lymphocytes (IEL) in the small intestine in terms of their expression of CD5, CD103 and Thy1.2. In addition, the Vgamma/delta repertoire of these gammadelta T cells was similar to that of gammadelta IEL. When DSS-treated mice were injected with IEL isolated from normal mice, IEL including gammadelta T cells preferentially migrated to PP, raising the possibility that B220+ T cells seen in PP of diseased mice may derive from IEL in the small intestine. Our present study suggests that PP might be able to accept T-cell lineages from intestinal IEL as well as from thymus-derived T cells.

Reasons why DBA/2 mice are resistant to malarial infection: expansion of CD3int B220+ gammadelta T cells with double-negative CD4- CD8- phenotype in the liver

DBA/2 (H-2(d)) mice are known to be more resistant than C57BL/6 (B6, H-2(b)) mice to the non-lethal 17XNL strain of Plasmodium yoelii. This is a very strange phenomenon because the functions of conventional T cells, especially CD8(+) T cells, are known to be somewhat lower in DBA/2 mice than in other strains of mice. We examined herein how immune responses differed between DBA/2 mice and B6 mice during malarial infection. DBA/2 mice and (DBA/2 x B6)F(1) (BDF(1), H-2(b/d)) mice were found to have milder parasitaemia and to recover more quickly from malarial infection than B6 mice. These DBA/2 and BDF(1) mice were also found to experience a marked expansion of interleukin (IL)-2Rbeta(+) CD3(int) cells and gammadelta T cells in the liver, especially in the recovery phase. The expansion of unconventional T cells (i.e. B220(+) T cells) was also marked in DBA/2 and BDF(1) mice. The majority of B220(+) T cells were gammadelta T cells and these T cells were double-negative CD4(-) CD8(-). More importantly, the production of immunoglobulin M (IgM)-type anti-DNA autoantibody was also higher in DBA/2 and BDF(1) mice than in B6 mice. In conjunction with data on cytokine production, these results indicate that primitive T and B cells, namely autoreactive extrathymic T cells and autoantibody-producing B cells, may be much more activated in DBA/2 mice and therefore resistant to the non-lethal 17XNL strain of P. yoelii.

Age-related bias in function of natural killer T cells and granulocytes after stress: reciprocal association of steroid hormones and sympathetic nerves

Stress-associated immune responses were compared between young (8 weeks of age) and old (56 weeks) mice. Since stress suppresses the conventional immune system (i.e. T and B cells) but inversely activates the primordial immune system (i.e. extrathymic T cells, NKT cells, and granulocytes), these parameters were analysed after restraint stress for 24 h. The thymus became atrophic as a function of age, and an age-related increase in the number of lymphocytes was seen in the liver. Although the number of lymphocytes in both the thymus and liver decreased as the result of stress, the magnitude was much more prominent in the thymus. To determine stress-resistant lymphocyte subsets, two-colour immunofluorescence tests were conducted in the liver and spleen. NKT cells were found to be such cells in the liver of young mice. On the other hand, an infiltration of granulocytes due to stress was more prominent in the liver of old mice than in young mice. Liver injury as a result of stress was prominent in young mice. This age-related bias in the function of NKT cells and granulocytes seemed to be associated with a difference in the responses of catecholamines (high in old mice) and corticosterone (high in young mice) after stress. Indeed, an injection of adrenaline mainly induced the infiltration of granulocytes while that of cortisol activated NKT cells. The present results suggest the existence of age-related bias in the function of NKT cells and granulocytes after stress and that such bias might be produced by different responses of sympathetic nerves and steroid hormones between young and old mice.

Mechanism of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced decrease in anti-CD3-activated CD4(+) T cells: the roles of apoptosis, Fas, and TNF

The environmental contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), suppresses T cell functions and reduces T cell numbers in multiple models of immune stimulation. However, the underlying mechanism(s) by which TCDD induces these changes has yet to be elucidated. We hypothesized that TCDD affects T cells through the induction or augmentation of apoptosis. In these studies, we used antibody to CD4, annexin V, and 7-AAD in three-color flow cytometric analyses to examine the relationship between the decrease in CD4(+) T cells and cell death in mice treated with anti-CD3 and TCDD. In addition, we examined two signaling pathways, Fas and TNF, in order to elucidate a potential mechanism by which TCDD increases cell death. Our results show that the TCDD-induced decrease in CD4(+) T cell number correlated with an increase in the percentage of dead cells, but not with cells expressing an early apoptotic phenotype. The TCDD-induced decrease in CD4(+) T cells was attenuated in Fas- and FasL-deficient mice (lpr and gld, respectively), but not by treatment with a neutralizing antibody to TNF. While these results suggest that the Fas pathway may be important in TCDD-induced T cell death, however, the effect of TCDD on the Fas pathway remains unclear. Taken together, our data suggest that TCDD-induced suppression of CD4(+) T cells involves, in part, increased cell death that may be mediated by Fas/FasL interaction.

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.

Increased TUNEL staining in brains of autoimmune Fas-deficient mice

Profound changes in brain morphology and behavior coincide with the spontaneous development of systemic autoimmune/inflammatory disease in Fas-deficient MRL-lpr mice. The dendrites atrophy, the density of hippocampal and cortical neurons decreases, and an anxious/depressive-like behavior emerges while lymphoid cells infiltrate into the choroid plexus of MRL-lpr mice. We hypothesized that the inherited lack of the Fas-dependent anti-inflammatory mechanism would lead to unsuppressed immune activity, characterized by reduced apoptosis in the MRL-lpr brain. Using the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeled (TUNEL) method as an indicator of apoptosis, a surprisingly high incidence of TUNEL-positive cells was observed in the hippocampus, choroid plexus and periventricular regions of MRL-lpr mice, 5-10-fold higher than that found in the MRL +/+ control brain. Immunostaining with anti-CD3, CD4 and CD8 monoclonal antibodies showed limited overlap between CD-positive and TUNEL-positive cells, suggesting that the dying cells are for the most part (approximately 70%) not T-lymphocytes. Although further characterization of the phenotype of the dying cells and the mechanism of cell death are required, the present results suggest the involvement of a Fas-independent apoptotic process in neurodegeneration induced by systemic autoimmune disease.

The majority of lymphocytes in the bone marrow, thymus and extrathymic T cells in the liver are generated in situ from their own preexisting precursors

Parabiotic pairs of B6.Ly5.1 and B6.Ly5.2 mice were used to investigate how lymphocytes in various organs and various lymphocyte subsets mixed with partner cells. The origin of partner cells was determined by using anti-Ly5.1 mAb in conjunction with immunofluorescence tests. Parabiosis was also produced after the irradiation of B6.Ly5.2 mice at various doses to prepare an immunosuppressive partner. Irrespective of irradiation, lymphocytes and other hematopoietic cells in the bone marrow and lymphocytes in the thymus showed a low mixture of partner cells in comparison with those of all other organs tested. On the other hand, lymphocytes in the blood, spleen, and lymph nodes became a half-and-half mixture of their own cells and partner cells by 14 days after parabiosis. Among lymphocyte subsets, intermediate CD3 cells (i.e., CD3int cells) and NKT cells (i.e., NK1.1+ subset of CD3int cells) in the liver also showed a low mixture of partner cells. The present results raise the possibility that lymphocytes in the bone marrow and thymus, and extrathymic T cells in the liver might be in situ generated from their own preexisting precursor cells. Another observation was that, after irradiation, partner cells showed accelerated mixture even if they showed a low mixture under non-irradiated conditions. However, only lymphocyte subsets with the same phenotype as those of preexisting cells entered the corresponding sites.

Mice with early onset of death (EOD) due to lupus glomerulonephritis

Both MRL-lpr/lpr (lpr) and BXSB mice fall victim to autoimmune disease as a function of age. To combine their properties, brother-sister mating of (female lpr x male BXSB)F1 mice was done. Mice for mating were selected according to indicators of early onset of glomerulonephritis and subsequent early death (i.e., EOD). This mating was continued for more than 16 generations. The EOD mice thus established had homozygous H-2k/k, lpr/lpr, and possible yaa/- (in the case of males). The average life span of males was 83 days while that of females was 126 days. After 12 weeks of age, the majority (> 80%) of male EOD mice were characterized by the abnormality of urine due to glomerulonephritis. We then characterized how glomerulonephritis was evoked, especially in terms of expanding lymphocyte subsets in various immune organs. Similar to the case of parental lpr mice, the major expanding cells were CD4-8-B220+ TCRint cells in the immune organs and kidney. In addition, myeloid cells were found to infiltrate the kidney. This massive infiltration of both TCRint cells and myeloid cells might be responsible for the onset of acute glomerulonephritis. Even after more than 50 generations, these EOD mice still carry both lpr and yaa genes. These results suggest that EOD mice might be a very useful tool for the study of acute lupus glomerulonephritis which is evoked by the genetic abnormalities.

Mechanisms involved in graft-versus-host disease induced by the disparity of minor histocompatibility M1s antigens

In this study we investigated which type of T cells: high T-cell receptor (TCRhigh, cells of thymic origin) or intermediate TCR (TCRint, cells of extrathymic origin), expanded in the liver and other organs, resulting in the induction of graft-versus-host disease (GVHD) with minor lymphocyte stimulating (M1s) disparity. When 6.5 Gy-irradiated BALB/c (H-2d M1s-1b2a) mice were injected with interleukin-2 receptor beta-chain(-) (IL-2Rbeta(-)) CD3high cells purified from the spleen of B10.D2 (H-2d M1s-1b2b) mice, IL-2Rbeta(+)CD3high cells expanded in the liver and other organs of recipient mice. The majority of these cells were found to be IL-2Ralpha(-)Mel-14(-)CD4(+)Vbeta3(+) in GVHD mice. The CDR3 region in their TCR-alphabeta (i.e. N-Dbeta-N) was polyclonal, although there were skewed usages of Vbeta3 and Jbeta2.4. The majority of cells were confirmed to be of donor origin by the individual discrimination method, namely, they originated from isolated IL-2Rbeta(-)CD3high cells. Interestingly, these T cells lacked cytotoxicity against both a natural killer (NK)-sensitive target and thymocytes with M1s disparity and nondisparity. Another important finding was that activated granulocytes expanded at generalized sites in GVHD mice. The present results raise the possibility that M1s disparity is mainly recognized by TCRhigh cells with unique properties but that direct effector cells that induce GVHD might not be such T cells but rather accompanied granulocytes.

Extrathymic derivation of gut lymphocytes in parabiotic mice

In adult mice, c-kit+ stem cells have recently been found in their liver, intestine and appendix, where extrathymic T cells are generated. A major population of such thymus-independent subsets among intraepithelial lymphocytes is T-cell receptor (TCR)gamma delta+ CD4- CD8alpha alpha+(beta-) cells, but the origins of other lymphocyte subsets are still controversial. In this study, we examined what type of lymphocyte subsets were produced in situ by such stem cells in the small intestine, large intestine and appendix. To investigate this subject, we used parabiotic B6.Ly5.1 and B5.Ly5. 2 mice which shared the same circulation by day 3. The origin of lymphocytes was identified by anti-Ly5.1 and anti-Ly5.2 monoclonal antibodies in conjunction with immunofluorescence tests. Lymphocytes in Peyer's patches and lamina propria lymphocytes (especially B cells and CD4+ T cells) in the small intestine became a half-and-half mixture of Ly5.1+ and Ly5.2+ cells in each individual of parabiotic pairs of mice by day 14. However, the mixture was low in CD8alpha alpha+, CD8alpha beta+ and gamma delta T cells in the small and large intestines and in CD3+ CD8+ B220+ cells in the appendix. These cells might be of the in situ origin. When one individual of a pair was irradiated before parabiosis, the mixture of partner cells was accelerated. However, a low-mixture group always continued to show a lower mixture pattern than did a high-mixture group. The present results suggest that extrathymic T cells in the digestive tract may arise from their own pre-existing precursor cells and remain longer at the corresponding sites.

Mice deficient in fas ligand (gld) or fas (lpr) show few alterations in granulopoiesis

Evidence exists that the life span of mature, circulating neutrophils is influenced by apoptosis induced by interactions between Fas ligand (FasL) and Fas (CD95). However, the role of FasL/Fas-mediated apoptosis in granulopoiesis has not been explored. The present study assessed differences in granulopoiesis between normal (B6) mice and mice carrying mutations in the genes for FasL (B6/gld) or Fas (B6/lpr). Granulopoiesis was examined by quantitating mature granulocytes in the blood, committed myeloid progenitor cells (or colony-forming units; CFU) in the bone marrow (BM), and granulocyte lineage cells in the BM. The present study also characterized through flow cytometry the ability of GR-1(+) granulocyte lineage cells from B6, B6/gld, and B6/lpr mice to undergo spontaneous apoptosis in vitro. In comparison to B6 mice, B6/gld mice (but not B6/lpr mice) showed small, but significant increases in the number and percentage of blood granulocytes and in the number of myeloid CFU. However, the number and percentage of GR-1(+) granulocyte lineage cells in the BM were similar in the three strains. The rate of spontaneous apoptosis of GR-1(+) granulocyte lineage cells also did not differ between B6, B6/gld, and B6/lpr mice. In B6 and B6/gld mice, Fas expression on granulocyte lineage cells was downregulated in conjunction with a decrease in forward-angle light scatter (fsc) and externalization of phosphatidylserine (PS), two measures of apoptosis. These results suggest that FasL-Fas interactions play only a minor role in modulating numbers of committed myeloid progenitor cells and the size of the peripheral pool of mature granulocytes. Interactions between FasL and Fas do not influence the size of the BM pool of granulocyte lineage cells or the ability of those cells to undergo spontaneous apoptosis.

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.

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.

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.

Expansion of an unusual population of Gr-1+CD3int cells in the lymph nodes and other peripheral organs of mice carrying the lpr gene

Granulocytes and extrathymic T cells are often activated simultaneously, but they are absolutely separate populations in normal mice. However, some abnormal extrathymic T cells (i.e., CD3int cells) seen in mice carrying the lpr gene were found to express a granulocyte marker, Gr-1. Such mice include MRL-lpr/lpr mice and SCG mice. In parallel with an age-associated increase of IL-2Rbeta(low)CD3int cells which contained double-negative CD4-8- and B220+CD2- cells, Gr-1+CD3int cells increased in number in the lymph nodes and other peripheral organs. In addition to a major population of IL-2Rbeta(low)CD3int cells, there is a small population of IL-2Rbeta(high)CD3int cells which produce normal Fas mRNA and Fas molecule from the lpr gene. It was found that both IL-2Rbeta(low)CD3int and IL-2Rbeta(high)CD3int cell populations contained Gr-1+ cells. IL-2Rbeta(high)CD3int cells tended to contain a higher proportion of Gr-1+ cells than did IL-2Rbeta(low)CD3int cells. More interestingly, Gr-1+CD3int cells expressed a considerable level of mRNA of the mG-CSF receptor, similar to granulocytes. The present study thus yielded further information on an unusual property of abnormally expanding CD3int cells in mice carrying the lpr gene.