E2A and HEB activate the pre-TCR alpha promoter during immature T cell development

The pre-TCRalpha (pTalpha) is exclusively expressed in immature thymocytes and constitutes the pre-TCR complex with TCRbeta, which regulates early T cell differentiation. Despite the recent identification of the pTalpha enhancer, the contribution of the promoter region, the direct DNA-protein interaction, and the regulation of such interaction along with T cell development have not been investigated. We analyzed the pTalpha promoter region and identified the critical elements for transcription of the pTalpha gene. The pTalpha promoter was found to contain two consecutive E-box elements that are critical for pTalpha transcription. The E-box elements in the promoter region formed the specific DNA-protein complex that was exclusively observed in immature thymocytes, not in mature thymocytes and T cells. The E proteins in this complex were identified as E2A and HeLa E-box binding protein (HEB), and overexpression of E2A and HEB resulted in activation of the pTalpha promoter. The binding complex in the consecutive E-boxes in the pTalpha promoter changed along with T cell development, as a distinct DNA-binding complex was observed in mature T cells. Comparing the E-box regions in the enhancer and the promoter, those in the promoter appear to make a greater contribution to pTalpha gene transcription.

Cutting edge: the mouse NK cell-associated antigen recognized by DX5 monoclonal antibody is CD49b (alpha 2 integrin, very late antigen-2)

DX5 mAb is a useful reagent because it stains NK cells from all mouse strains examined. We have identified the molecule recognized by DX5 mAb by using a retrovirus-mediated expression cloning system. A 5-kb cDNA encoding a protein that is reactive with the DX5 mAb was isolated from a NK cell cDNA library, and this molecule was identical with CD49b (very late Ag-2, alpha(2) integrin). The DX5 mAb reacted with transfectants expressing CD49b, and binding of DX5 to the NK cells and CD49b transfectants was blocked in the presence of other anti-CD49b mAbs. When NK1.1(+) NK cells were cultured with IL-2, they progressively lost reactivity with DX5 mAb as a consequence of cellular proliferation. Cytotoxicity mediated by the DX5(+) NK cells was dramatically higher as compared with DX5(-) NK cells. Therefore, DX5 mAb recognizes CD49b and can be used to define functionally distinct subsets of NK cells.

Cytokine-independent Jak3 Activation upon T Cell Receptor (TCR) Stimulation through Direct Association of Jak3 and the TCR Complex

Jak3 is responsible for growth signals by various cytokines such as interleukin (IL)-2, IL-4, and IL-7 through association with the common gamma chain (gammac) in lymphocytes. We found that T cells from Jak3-deficient mice exhibit impairment of not only cytokine signaling but also early activation signals and that Jak3 is phosphorylated upon T cell receptor (TCR) stimulation. TCR-mediated phosphorylation of Jak3 is independent of IL-2 receptor/gammac but is dependent on Lck and ZAP-70. Jak3 was found to be assembled with the TCR complex, particularly through direct association with CD3zeta via its JH4 region, which is a different region from that for gammac association. These results suggest that Jak3 plays a role not only in cell growth but also in T cell activation and represents cross-talk of a signaling molecule between TCR and growth signals.

Negative regulation of expression and function of Fc gamma RIII by CD3 zeta in murine NK cells

Fc gamma RIII is involved in Ab-dependent cell-mediated cytotoxicity (ADCC) and cytokine production by NK cells. Signaling and expression of Fc gamma RIII are dependent on FcR gamma. Although NK cells express not only FcR gamma but also CD3 zeta, the role of CD3 zeta in NK cell function remains unclear. Here, we found that the expression of Fc gamma RIII on NK cells from CD3 zeta-deficient mice is unexpectedly up-regulated compared with that on cells from normal mice. Furthermore, ADCC and IFN-gamma production upon Fc gamma RIII-cross-linking by NK cells from CD3 zeta-deficient mice were also up-regulated. Up-regulation of the surface expression of Fc gamma RIII on CD3 zeta-deficient NK cells is not mediated by transcriptional augmentation of either Fc gamma RIII or FcR gamma gene because there was no significant difference in the expression of mRNA for Fc gamma RIII and FcR gamma. Transfection of CD3 zeta into a cell line expressing Fc gamma RIII and FcR gamma induced a decrease in the cell surface expression of Fc gamma RIII. These findings reveal a negative regulatory role of CD3 zeta in Fc gamma RIII-mediated function of murine NK cells.

The quantity of TCR signal determines positive selection and lineage commitment of T cells

It is generally accepted that the avidity of TCR for self Ag/MHC determines the fate of immature thymocytes. However, the contribution of the quantity of TCR signal to T cell selection has not been well established, particularly in vivo. To address this issue, we analyzed DO-TCR transgenic CD3zeta-deficient (DO-Tg/zetaKO) mice in which T cells have a reduced TCR on the cell surface. In DO-Tg/zetaKO mice, very few CD4 single positive (SP) thymocytes developed, indicating that the decrease in TCR signaling resulted in a failure of positive selection of DO-Tg thymocytes. Administration of the peptide Ag to DO-Tg/zetaKO mice resulted in the generation of functional CD4 SP mature thymocytes in a dose-dependent manner, and, unexpectedly, DO-Tg CD8 SP cells emerged at lower doses of Ag. TCR signal-dependent, sequential commitment from CD8(+) SP to CD4(+) SP was also shown in a class I-restricted TCR-Tg system. These in vivo analyses demonstrate that the quantity of TCR signal directly determines positive and negative selection, and further suggest that weak signal directs positively selected T cells to CD8 lineage and stronger signal to CD4 lineage.

Regulation of cell surface expression of CTLA-4 by secretion of CTLA-4-containing lysosomes upon activation of CD4+ T cells

CTLA-4 is expressed on the surface of activated T cells and negatively regulates T cell activation. Because a low-level expression of CTLA-4 on the cell surface is sufficient to induce negative signals in T cells, the surface expression of CTLA-4 is strictly regulated. We previously demonstrated that the association of CTLA-4 with the clathrin-associated adaptor complex AP-2 induces internalization of CTLA-4 and keeps the surface expression low. However, the mechanism to induce high expression on the cell surface upon stimulation has not yet been clarified. To address this, we investigated the intracellular dynamics of CTLA-4 by analyzing its localization and trafficking in wild-type and mutant CTLA-4-transfected Th1 clones. CTLA-4 is accumulated in intracellular granules, which we identified as lysosomes. CTLA-4 is degraded in lysosomes in a short period, and the degradation process may serve as one of the mechanisms to regulate CTLA-4 expression. Upon TCR stimulation, CTLA-4-containing lysosomes are secreted as proven by the secretion of cathepsin D and beta-hexosaminidase in parallel with the increase of surface expression of CTLA-4 and lysosomal glycoprotein 85, a lysosomal marker. These results suggest that the cell surface expression of CTLA-4 is up-regulated upon stimulation by utilizing a mechanism of secretory lysosomes in CD4(+)T cells.

A Di-leucine signal in the ubiquitin moiety. Possible involvement in ubiquitination-mediated endocytosis

Some plasma membrane receptors in yeast are known to be internalized and degraded in lysosomes upon ligand-dependent ubiquitination. However, the role of ubiquitination in endocytosis and lysosomal degradation in higher eukaryotes has been controversial. In order to directly assess this question, we investigated the fate of chimeric molecules in which ubiquitin moiety was fused in-frame to the cytoplasmic region of membrane proteins. The chimeric proteins with the wild-type ubiquitin were endocytosed and delivered to lysosomes efficiently. Mutant ubiquitin with lysine-to-arginine substitution could still mediate endocytosis, suggesting that polyubiquitination is not required for the endocytosis. We next searched for the existence of an endocytosis signal(s) in the ubiquitin moiety, and identified a di-leucine signal, Leu(43)-Ile(44). The Leu(43)-Ile(44) sequence mediated endocytosis and lysosomal sorting in a Leu(43)-dependent manner. These results suggest that the di-leucine signal in ubiquitin can be involved in ubiquitination-mediated endocytosis and lysosomal targeting of membrane proteins.

Immune complex and Fc receptor-mediated augmentation of antigen presentation for in vivo Th cell responses

It has recently been established that FcRs are involved in the triggering of type II and III inflammatory responses. Although FcR is not believed to be involved in the regulation of T cell function, the in vivo contribution of FcRs to T cell function still remains unclear. We analyzed in vivo responses of delayed-type hypersensitivity and proliferation of CD4+ T cells to Ags in FcRgamma-/- mice lacking the expression and function of FcgammaRI, FcgammaRIII, and FcepsilonRI. We found that the delayed-type hypersensitivity response in FcRgamma-/- mice is significantly decreased compared with that in wild-type mice. Moreover, the secondary responses of proliferation and cytokine production as well as the Ab formation by CD4+ T cells from FcRgamma-/- mice to Ag and normal APCs were also reduced. In contrast, in vitro primary T cell proliferative responses upon stimulation with anti-TCR Ab or MLR as well as in vivo primary response against staphylococcus enterotoxin B administration were not different between T cells from FcRgamma-/- and wild-type mice. In addition, the Ag presentation function of APCs from unimmunized FcRgamma-/- mice was normal. On the other hand, Ab-deficient mice also revealed impaired T cell responses. These results demonstrate that the defective T cell responses in FcRgamma-/- mice were due to impaired Ag presentation during in vivo priming not to a defect in T cells. Therefore, they suggest that the FcRs on APCs mediate efficient priming of Th cell responses in vivo in an immune complex-dependent manner.

Ablation of a specific cell population by the replacement of a uniquely expressed gene with a toxin gene

The transgenic expression of a toxin gene or a thymidine kinase gene under the control of cell type-specific promoter/enhancer has been shown to be useful for removing a specific cell population in mice. However, this approach requires extensive analysis of the control elements for gene expression in the preparation of the transgenic constructs, and furthermore, the toxin gene might be expressed ectopically because of random integration, resulting in aberrant depletion of unrelated cells. To avoid such difficulties with the transgenic approach, we established a method for the specific depletion of a cell population by replacing a uniquely expressed gene in the population with the diphtheria toxin gene by using homologous recombination. The NKR-P1 gene, a specific cell surface marker of natural killer (NK) cells, was selected as the target gene for depleting NK cells. In chimeric mice reconstituted with embryonic stem cells in which the NKR-P1 gene was replaced by the toxin gene, NKR-P1(+) cells were almost completely depleted, and NK cell function was abrogated in the embryonic stem cell-derived lymphoid cells. Other cell lineages developed normally. These results show that all NK cells express NKR-P1, that NKR-P1(+) cells do not influence the development of T and B cells, and further, that this technology of cell targeting is a fast and powerful method of generating mice lacking any chosen cell population.

Resistance of Fc receptor- deficient mice to fatal glomerulonephritis

Immune complex-mediated inflammation is a common mechanism of various autoimmune diseases. Glomerulonephritis (GN) is one of these diseases, and the main mechanism of the induction of GN has been unclear. We examined the contribution of Fc receptors in the induction of nephrotoxic GN by establishing and analyzing mice deficient in the Fc receptor gamma chain (FcRgamma). Whereas all wild-type mice died from severe glomerulonephritis with hypernitremia by administration of anti-glomerular basement membrane (GBM) antibodies, all FcRgamma-deficient mice survived. Histologically, wild-type mice showed glomerular hypercellularity and thrombotic changes, whereas the renal tissue in FcRgamma-deficient mice was almost intact. Deposition of anti-GBM antibody as well as complement components in the GBM were equally observed in both wild-type and knockout mice. These results demonstrate that the triggering of this type of glomerulonephritis is completely dependent on FcR+ cells.

Association with FcRgamma is essential for activation signal through NKR-P1 (CD161) in natural killer (NK) cells and NK1.1+ T cells

Natural killer (NK) cells exhibit cytotoxicity against variety of tumor cells and virus-infected cells without prior sensitization and represent unique lymphocytes involved in primary host defense. NKR-P1 is thought to be one of NK receptors mediating activation signals because cross-linking of NKR-P1 activates NK cells to exhibit cytotoxicity and IFN-gamma production. However, molecular mechanism of NK cell activation via NKR-P1 is not well elucidated. In this study, we analyzed the cell surface complex associated with NKR-P1 on NK cells and found that NKR-P1 associates with the FcRgamma chain which is an essential component of Fc receptors for IgG and IgE. The association between FcRgamma and NKR-P1 is independent of Fc receptor complexes. Furthermore, NK cells from FcRgamma-deficient mice did not show cytotoxicity or IFN-gamma production upon NKR-P1 cross-linking. Similarly, NK1.1+ T cells from FcRgamma-deficient mice did not produce IFN-gamma upon NKR-P1 crosslinking. These findings demonstrate that the FcRgamma chain plays an important role in activation of NK cells via the NKR-P1 molecule.

Th1 and Th2 subsets equally undergo Fas-dependent and -independent activation-induced cell death

Stimulation of previously activated T cells results in apoptosis, termed activation-induced cell death (AICD). Recent analysis revealed that the Fas/Fas ligand (FasL) interaction is predominantly involved in AICD of T cells. Furthermore, based on the analysis of various T cell clones and lines, it has been reported that FasL is expressed mainly in Th1 but not in Th2 cells. However, the exact expression pattern of FasL and its function in normal activated T cells has not been determined. In the present study, by utilizing completely differentiated Th1 and Th2 cell populations obtained from ovalbumin-specific T cell receptor (TCR)-transgenic mice, the FasL expression on Th1 and Th2 was determined. Furthermore, involvement of Fas-FasL interaction in AICD of Th1 and Th2 cells was analyzed by two approaches: one was the inhibition of AICD by anti-FasL monoclonal antibodies, and the other AICD of Th1/Th2 subsets from TCR-transgenic mice backcrossed to lpr mice. We demonstrated that Th2 cells express FasL on the cell surface at a level similar to that expressed by Th1 cells, and that both subsets were equally susceptible to the Fas-mediated AICD. These observations suggest not only that the expression of FasL is not always correlated with Th subsets as defined by the cytokine-producing profile, but also that the responses of both Th1 and Th2 subsets are regulated by Fas-mediated AICD. Finally, analysis of the kinetics of AICD revealed a novel Fas/FasL-independent pathway in its initial stage. These findings revealed the precise function of Fas/FasL-mediated as well as Fas/FasL-independent AICD in the regulation of helper T cell responses.

Influence of graft versus host reaction on the T cell repertoire differentiating from bone marrow precursors following allogeneic bone marrow transplantation

When lethally irradiated AKR (Mls-1a) mice were reconstituted with bone marrow (BM) cells plus a small number (0.5%) of mature T cells from allogeneic B10.AQR or B10 (Mls-1b) mice and minor GVHR was induced in the recipients, almost complete donor chimerism was accomplished in the early stages after reconstitution. By contrast, in irradiated AKR mice reconstituted with T cell-depleted BM cells alone from B10 or B10.AQR mice, radio-resistant T cells of recipient origin persisted for a relatively long period in peripheral lymphoid tissues. In this paper the influence of residual T cells in the chimeric mice on generation of the T cell repertoire derived from donor BM is discussed. It will be demonstrated that the recipient (AKR) T cells are capable of producing Mls-1a antigens (Ag) after lethal irradiation in vivo. These recipient T cells eventually induce clonal elimination of Mls-1a reactive V beta 6+, V beta 8.1+ and V beta 9+ T cells derived from developing thymocytes of donor BM origin. The Mls-1a reactive T cells are not eliminated in GVHR chimeras in which recipient T cells are absent. However, V beta 5+ T cells reactive to I-E plus Etc-1 Ag are deleted in the chimeras undergoing GVHR. These results indicate that recipient cells which produce tissue-specific antigens (tolerogens) should be taken into consideration when generation of the T cell repertoire of donor origin following allogeneic BM transplantation is investigated.

A shift from negative to positive selection of autoreactive T cells by the reduced level of TCR signal in TCR-transgenic CD3 zeta-deficient mice

T cell selection is thought to be determined through the interaction between TCR and Ag/MHC. However, the contribution of the level of TCR signal to thymic selection remains unclear. To address this issue, we analyzed T cell selection of male Ag (HY)-specific TCR transgenic (HYTg) mice crossed with CD3 zeta-deficient (zeta KO) mice (HYTg/zeta KO), which have impaired signaling through TCR. In male HYTg/zeta KO mice, the number of thymocytes was comparable to that in normal mice, and almost all the peripheral T cells were HY specific, although these positively selected cells were anergic to male Ag. From these observations, the decrease in TCR signaling by CD3 zeta deficiency resulted in both the avoidance of negative selection and the acquisition of positive selection of autoreactive T cells in male HYTg/zeta KO mice. There was a shift of T cell selection from positive to no selection of HY-specific T cells in female HYTg/zeta KO mice also. Collectively, these findings suggest that the level of TCR signal directly regulates T cell selection; furthermore, the findings have integrated the models of T cell selection into a concept based on the quantity of TCR signal.

A shift from negative to positive selection of autoreactive T cells by the reduced level of TCR signal in TCR-transgenic CD3 zeta-deficient mice

T cell selection is thought to be determined through the interaction between TCR and Ag/MHC. However, the contribution of the level of TCR signal to thymic selection remains unclear. To address this issue, we analyzed T cell selection of male Ag (HY)-specific TCR transgenic (HYTg) mice crossed with CD3 zeta-deficient (zeta KO) mice (HYTg/zeta KO), which have impaired signaling through TCR. In male HYTg/zeta KO mice, the number of thymocytes was comparable to that in normal mice, and almost all the peripheral T cells were HY specific, although these positively selected cells were anergic to male Ag. From these observations, the decrease in TCR signaling by CD3 zeta deficiency resulted in both the avoidance of negative selection and the acquisition of positive selection of autoreactive T cells in male HYTg/zeta KO mice. There was a shift of T cell selection from positive to no selection of HY-specific T cells in female HYTg/zeta KO mice also. Collectively, these findings suggest that the level of TCR signal directly regulates T cell selection; furthermore, the findings have integrated the models of T cell selection into a concept based on the quantity of TCR signal.

Crucial role of Jak3 in negative selection of self-reactive T cells

Jak3 mediates growth signals through cytokine receptors such as interleukin-2 (IL-2), IL-4, and IL-7, and its deficiency results in autosomal recessive SCID in mice and humans. In spite of the severely reduced number of lymphocytes in Jak3-deficient mice, the differentiation profile of thymocytes was normal and mature T cells accumulated in the periphery with age. However, we found that self-reactive T cells were not deleted in the thymus and the peripheral tissues in Jak3-deficient mice. All peripheral T cells were in the activation state and thus were unable to be activated further, as demonstrated by the failure of eliciting Ca2+ response upon T cell receptor (TCR) stimulation. From the analysis of TCR-transgenic Jak3-deficient mice, only self-reactive T cells appeared to be in the activated state and anergic. These findings demonstrate a crucial function of Jak3 in the negative selection of autoreactive T cells and the maintenance of functional peripheral T cells.

Preferential requirement of CD3 zeta-mediated signals for development of immature rather than mature thymocytes

Antigen recognition signals by the TCR are transduced through activation motifs present in the cytoplasmic region of CD3 chains. In vitro analysis has suggested that the CD3zeta chain mediates different signals from other CD3 chains. To analyze the in vivo function of CD3zeta-mediated signals for T cell development, mice expressing a mutant CD3zeta chain lacking all the activation motifs were generated by introducing the transgene into zeta-knockout mice. Mature CD4(+) single-positive (SP) thymocytes in these mice were greater in number than in zeta-deficient mice, and the promoted differentiation was indicated by the changes of CD69 and HSA phenotypes. We found that even in the absence of activation motifs in CD3zeta, these mature cells became functional, being able to induce Ca2+ mobilization and proliferation upon stimulation. On the other hand, CD4(-)CD8(-) double-negative (DN) thymocytes, most of which were arrested at the CD44(-)CD25(+) stage similarly to those in zeta-deficient mice, could not be promoted for differentiation into CD4(+)CD8(+) double-positive thymocytes in these mice in spite of the fact that the expression of the transgene in DN thymocytes was higher than that of zeta in wild-type mice. These results demonstrate the preferential dependence of the promotion of development and/or expansion of DN thymocytes rather than mature thymocytes upon the activation signals through the zeta chain and suggest differential requirements of TCR signaling for mature SP and immature DN thymocyte developments in vivo.

Interferon gamma production by natural killer (NK) cells and NK1.1+ T cells upon NKR-P1 cross-linking

Natural killer (NK) cells play an important role in immune response by producing interferon gamma (IFN-gamma) as well as exhibiting cytotoxic function. IFN-gamma produced by NK cells has been suggested to be involved in differentiation of T helper cells. On the other hand, the NKR-P1 molecule was recently identified as one of the important NK cell receptors, and it recognizes certain kinds of oligosaccharides on target cells and triggers NK cells for cytotoxicity. In the present study, we found that NK cells produce great amounts of IFN-gamma upon cross-linking of the NKR-P1 molecule. In contrast, stimulation of NK cells with IL-2 induced proliferation without producing IFN-gamma. Similar to NK cells, NK1.1+ T cells also produced IFN-gamma upon NKR-P1 cross-linking. NK1.1+ T cells produced IFN-gamma but not interleukin 4 (IL-4) upon NKR-P1 cross-linking, whereas they secreted both IFN-gamma and IL-4 upon T cell receptor cross-linking. These results indicate that NKR-P1 is a receptor molecule on NK and NK1.1+ T cells that induces not only cytotoxicity but also IFN-gamma production. Our findings provide a new pathway for IFN-gamma production by NK and NK1.1+ T cells through NKR-P1 molecules; it may be essential for immune regulation.

Mitogenic effect of HIV-infected human T cell lines on mouse B cells mediated by surface immunoglobulin

Following HIV-1 infection, a number of disorders are induced in both normal T and B cells by virus products derived from infected CD4+ T cells. In the present study, we found that HIV-infected, but not uninfected, human T cell lines generated vigorous blastogenesis and proliferation of freshly isolated mouse B cells in a short-term culture. Neither human B cells nor rat B cells showed significant responses to the HIV-infected T cell lines in the present condition. The mitogenic effect of HIV-infected human T cell line requires direct cell-cell interaction between mouse B cells and HIV-infected T cell lines. Since either mitomycin c treatment or paraformaldehyde fixation of HIV-infected T cell lines resulted in complete loss of the mitogenic effect, it seems that de novo synthesized viral products are responsible for this effect. Furthermore, anti-mouse immunoglobulin antibody inhibited completely the B cell stimulation by the HIV-infected human T cell lines. Thus, surface immunoglobulin (sIg) on mouse B cells appears to be an essential molecule which transduces activation signals from HIV-infected human T cells into cytoplasm of the B cells.

Developmental defects of lymphoid cells in Jak3 kinase-deficient mice

Jak3 is a tyrosine kinase mediating cytokine receptor signaling through the association with the common gamma chain of the cytokine receptors such as IL-2, IL-4, IL-7, IL-9, and IL-15. Unlike other members of the Jak family, the expression of Jak3 is highly restricted in hematopoietic cells. To elucidate in vivo function of Jak3, Jak3-deficient mice were generated by homologous recombination. Mice homozygous for Jak3 null mutation showed severe defects, specifically in lymphoid cells. B cell precursors in bone marrow, thymocytes, and both T and B cells in the spleen drastically decreased, although these defects were significantly recovered as aging occurred. Peripheral lymph nodes, NK cells, dendritic epidermal T cells, and intestinal intraepithelial gamma delta T cells were absent. Normal number of hematopoietic stem cells in bone marrow from Jak3-deficient mice and the similar capability to generate myeloid and erythroid colonies as wild-type mice indicated specific defects in lymphoid stem cells. Furthermore, the abnormal architecture of lymphoid organs suggested the involvement of Jak3 in the function of epithelial cells. T cells developed in the mutant mice did not respond to either IL-2, IL-4, or IL-7. These findings establish the crucial role of Jak3 in the development of lymphoid cells.

[Pharmacokinetics of SK & F 104864 in experimental animals. II. Tissue distribution]

After intravenous bolus injection of a camptothecin derivative, SK & F 104864 (topotecan), at 20 mg/kg into Sarcoma 180 bearing mice, the tissue concentration of total topotecan (SK & F 104864 plus SK & F 105992) in the mice decreased bi-exponentially, and the beta half-lives in most tissues were longer than those in plasma. The AUCs of total topotecan were extremely large in the kidney, that was followed by the pancreas > intestine > stomach > spleen > liver > thymus > lung > tumor > uterus > plasma. The concentration of total topotecan after 24 hours decreased to less than 2% of the peak level in most tissues except the kidney.

Developmental arrest of NK1.1+ T cell antigen receptor (TCR)-alpha/beta+ T cells and expansion of NK1.1+ TCR-gamma/delta+ T cell development in CD3 zeta-deficient mice

The relationship between the structure of the T cell antigen receptor (TCR)-CD3 complex and development of NK1.1+ T cells was investigated. The TCR complex of freshly isolated NK1.1+ TCR-alpha/beta+ thymocytes contained CD3 zeta homodimers and CD zeta-FcR gamma heterodimers, whereas that of the majority of NK1.1- T cells did not contain FcR gamma. The function of CD3 zeta and FcR gamma in the development of NK1.1+ T cells was determined by analyzing CD3 zeta- and FcR gamma-deficient mice. The NK1.1+ T cells from wild-type and CD3 zeta-deficient mice had equal levels of CD3 expression. However, the development of NK1.1+ TCR-alpha/beta+ T cells was almost completely disrupted in thymus and spleen in CD3 zeta-deficient mice, whereas no alteration was observed in FcR gamma-deficient mice. In contrast, the number of novel NK1.1+ TCR-gamma/delta+ thymocytes expressing a surface phenotype similar to NK1.1+ TCR-alpha/beta+ thymocytes increased approximately six times in CD3 zeta-deficient mice. These findings establish the distinct roles of the CD3 zeta chain in the development of the following different thymic T cell compartments: NK1.1- TCR+, NK1.1+ TCR-alpha/beta+, and NK1.1+ TCR-gamma/delta+ thymocytes, which cannot be replaced by CD3 eta or FcR gamma chains.

Production of minor lymphocyte stimulatory-1a antigens from T cell subsets

T cell subsets that produce minor lymphocyte stimulatory (Mls) antigens were analyzed using mixed lymphocyte reaction (MLR) in vitro or clonal elimination assay in vivo. When lymph node T cells from B10.BR(Mls-1b) mice were stimulated with various T cell subsets from AKR (Mls-1a) mice in the presence of B10.BR antigen presenting cells (APC), proportions of Mls-1a reactive T cell blasts (V beta 6+, V beta 8.1+) increased. The stimulatory potency of CD8+ T cells was higher than that of CD4+ T cells. Furthermore, among either CD8+ or CD4+ T cell subset, CD44+ T cells appeared to produce larger amounts of Mls-1a antigens than CD44- T cells. More marked difference was demonstrated, when stimulator AKR T cells were being activated by immobilized anti-T cell antigen receptor (TCR) antibody during MLR. Thus, AKR T cells appeared to produce large amounts of Mls-1a antigens on appropriate stimulations. These findings were confirmed by the semiquantitative analysis of mRNA levels of MTV-7 in the AKR T cell subsets. When CD8+CD44+ T cells from (AKR x B10.BR)F1 mice were injected intravenously into [B10.BR-->B10.BR] syngeneic bone marrow (BM) chimeras 1 week after BM reconstitution and proportions of V beta 6+ T cells were quantitated 7 weeks later, significant clonal elimination of V beta 6+ T cells was induced among both thymocyte population and lymph node T cell population in a dose-dependent manner of the inoculated F1 T cells. Inoculation of CD8+CD44-F1 T cells eliminated V beta 6+ T cells less efficiently from lymph node T cells and inoculation of CD4+F1 T cells induced no significant clonal elimination of the V beta 6+ T cells. The present findings demonstrate clearly that CD8+CD44+ T cells represent the cells producing large amounts of Mls-1a antigens and inducing clonal elimination of V beta 6+ T cells in vivo.

Differential contribution of the FcR gamma chain to the surface expression of the T cell receptor among T cells localized in epithelia: analysis of FcR gamma-deficient mice

The function of the Fc receptors gamma chain (FcR gamma) for the expression of the T cell receptor (TCR) complex and for T cell development, especially for T cells localized in epithelia, was investigated by analyzing FcR gamma-deficient mice. In wild-type mice, CD8 alpha alpha + beta -TCR alpha beta + T cells of intestinal intraepithelial lymphocytes (i-IEL) utilized CD3 zeta homodimers and zeta-FcR gamma heterodimers, whereas CD8 alpha alpha + beta -TCR gamma delta + i-IEL used zeta-FcR gamma and FcR gamma homodimers in the TCR complex. On the other hand, these T cells in FcR gamma-deficient mice contained only zeta homodimers. The surface expression of the TCR complex was reduced in CD8 alpha alpha + beta -i-IEL and dendritic epidermal T cells (DETC) in these mice, whereas the development of these T cells was normal. The degree of reduction appeared to depend on the expression level of FcR gamma. In contrast to these populations, TCR gamma delta + intraepithelial T cells in reproductive organs (r-IEL) were dramatically decreased, suggesting that the development of r-IEL is FcR gamma-dependent, probably due to the predominant usage of FcR gamma homodimers in the TCR complex. These results indicate that the FcR gamma chain contributes differently to the TCR expression and to the development of T cells localized in epithelia.

Fas-mediated cytotoxicity by freshly isolated natural killer cells

The expression of Fas ligand on natural killer (NK) cells and Fas-mediated cytotoxicity by NK cells was investigated. Fas ligand mRNA was expressed in freshly isolated NK cells but not in T cells. Furthermore, the Fas ligand was detected on the cell surface of NK cells by staining with soluble Fas molecule. We analyzed the cytolytic activity of NK cells against thymocyte targets from normal and lpr mice, and found that the NK cells killed thymocytes from normal mice but not from lpr mice. On the other hand, splenic T cells did not show any cytotoxicity against either of the thymocyte targets. Similarly, NK cells exhibited cytotoxicity against transfectants expressing Fas antigen but not against parental cells or transfectants expressing a mutant Fas antigen with deleted cytoplasmic region. These results demonstrated that NK cells express Fas ligand and possess the capability of killing target cells expressing Fas antigen on their surface. This finding suggests that NK cells play an important role by eliminating Fas-expressing cells either constitutively or inducibly in peripheral lymphoid organs.

Comparative analyses of thymocyte and thymic low-density adherent cell functions

Thymocytes which have developed in the C3H thymus showed depressed proliferative responses to stimulation with anti-CD3 antibody as compared with those which have developed in the thymus of other strains of mice (i.e. AKR). The present study was conducted to analyze immunological functions of the thymic stromal cell population (low-density adherent cells, LDAC) in the C3H mice using allogeneic bone marrow (BM) chimeras established by BM transplantation in the reciprocal combination of AKR and C3H mice as donor or recipient. The thymic LDAC from C3H mice or the [AKR(donor)-->C3H(recipient)] chimeras contained a high proportion of Mac-1+ cells as compared to AKR mice or the [C3H-->AKR] chimeras. The proportion of Mac-1+ cells paralleled the IL-1- and PGE2-secreting ability of the LDAC cultured either in the presence or absence of LPS and also paralleled the antigen-presenting cell functions of the LDAC. Furthermore, after anti-CD3 stimulation the PGE2 inhibited more profoundly proliferative responses of [AKR-->C3H] or normal C3H thymocytes than those of the [C3H-->AKR] chimera or normal AKR thymocytes. A PGE2 inhibitor, indomethacin, reversed the depressed responses of the thymocytes which had developed in the C3H thymus. These findings suggest that the lower responsiveness of thymocytes from [AKR-->C3H] chimeras to anti-CD3 stimulation may be attributable to large amounts of PGE2 secreted by LDAC and/or to increased sensitivity of thymocytes themselves to PGE2.

Cytotoxicity of fresh NK1.1+ T cell receptor alpha/beta+ thymocytes against a CD4+8+ thymocyte population associated with intact Fas antigen expression on the target

Recent studies have revealed that 10-20% of CD4+8- or CD4-8- thymocyte populations contain NK1.1+ T cell receptor (TCR)-alpha/beta+ cells. This subpopulation shows characteristics that are different from NK1.1- CD4+ or NK1.1- CD8+ T cells and seems to have developed in a manner different from NK1.1- T cells. Although extensive studies have been performed on the NK1.1+ TCR-alpha/beta+ thymocytes, the physiological role of the NK1.1+ TCR-alpha/beta+ thymocytes has been totally unclear. In the present study, we found that freshly isolated NK1.1+ TCR-alpha/beta+ thymocytes, but neither whole thymocytes nor lymph node T cells, directly killed CD4+8+ thymocytes from normal syngeneic or allogeneic mice by using a long-term cytotoxic assay in which flow cytometry was used to detect the cytotoxicity. However, only weak cytotoxicity was detected against thymocytes from lpr mice on which the Fas antigen that transduces signals for apoptosis into the cells is not expressed. Furthermore, the NK1.1+ TCR-alpha/beta+ thymocytes exhibited high cytotoxicity against T lymphoma targets transfected with fas genes as compared with the parental T lymphoma targets or target cells transfected with mutated fas genes, which lack the function of transducing signals. On the other hand, NK1.1+ effector thymocytes from gld mice that carry a point mutation in Fas ligand did not kill thymocyte targets from normal mice. The present findings, thus, consistently suggest that the NK1.1+ TCR-alpha/beta+ thymocytes kill a subpopulation among CD4+8+ thymocytes via Fas antigen and in this way regulate generation of T lineage cells in the thymus.

Contribution of host radioresistant T cells to the clonal elimination of minor lymphocyte stimulatory-1a reactive T cells in mouse bone marrow chimeras

When bone marrow (BM) cells from I-E+ and minor lymphocyte stimulatory (Mls) antigen (Ag) disparate mice (Mls-1b) were transplanted to lethally irradiated Mls-1a mice, Mls-1a reactive T cells were found to be completely deleted from the developing thymocyte population in these [Mls-1b-->Mls-1a] radiation chimeras. It has been shown that BM-derived class II (Ia) positive cells play an essential role in this clonal deletion. Thus, Mls-1a Ag appeared to have been transferred from recipient cells to the Ia+ cells derived from donor BM. These Mls-1a-Ia complexes appear to be responsible for elimination of the Mls-1a reactive T cells that have also been derived from donor BM. However, definition of the cells of the recipient that generate the Mls-1a Ag and transfer them to the BM-derived Ia+ cells has remained unclear to date. In the analysis described herein, we have investigated the tolerogenicity of Mls-1a Ag derived from host T cells which represent a major population of radioresistant cells in the [Mls-1b-->Mls-1a] chimeras. When recipient T cells that had been collected and purified from spleens of [Mls-1b-->Mls-1a] chimeras were administered i.v. into [Mls-1b] chimeras, Mls-1a reactive V beta 6+, V beta 8.1+, or V beta 9+ T cells were completely eliminated. Thus, residual radioresistant host T cells present in the radiation BM chimeras are the cells which produce the Mls-1a Ag. These Mls-1a Ags ultimately contribute to the clonal elimination of Mls-1a reactive T cells from the developing thymocyte population. The present findings indicate that recipient T cells which can survive lethal irradiation and produce intrinsic superantigens alter eventually the T cell repertoire in the thymus which have been developing from precursors of donor BM.

Functional studies on MEL-14+ and MEL-14- T cells in peripheral lymphoid tissues

Functions of MEL-14+ T cells and MEL-14- T cells in peripheral lymphoid tissues were analyzed and compared. The MEL-14- T cells, representing a minor subpopulation of spleen and lymph node T cells, generated considerably higher mixed lymphocyte reaction and mitogen responses than the MEL-14+ T cells in any lymphoid tissues studied. Furthermore, upon stimulation with ConA the MEL-14- CD8+ T cells produced significantly larger amounts of IL-2 and IFN-gamma than MEL-14+ CD8+ T cells did. A similar but less marked observation was obtained with the CD4+ T cell population. Furthermore, when B10.BR mice were immunized with AKR (Mls-1a) spleen cells, the proportion of the Mls-1a reactive V beta 6+ T cells from draining lymph nodes increased and a substantial proportion of the increasing V beta 6+ T cells was shown to be MEL-14-. The present findings on the whole indicate that MEL-14- T cells in the peripheral lymphoid tissues are at functionally high levels and may represent memory cells which have been previously stimulated in vivo.

Production of minor lymphocyte stimulatory-1a antigen from activated CD4+ or CD8+ T cells

Minor lymphocyte stimulatory (Mls) Ag are super Ag that stimulate a high proportion of T cells of a specific TCR V beta family. One of the super Ag, Mls-1a, which is recognized mainly by TCR V beta 6+ and V beta 8.1+ T cells, has recently been linked to the response to product of the open reading frame in 3'-long terminal repeat of endogenous mammary tumor virus, MTV-7. It is quite certain that B cells are able to produce and also to present the Mls-1a Ag. However, it remains to be determined whether other cell types, especially T cells, produce Mls-1a Ag. In this study using highly purified T cell subpopulations, capacity to produce Mls-1a Ag was analyzed by calculating the proportion of Mls-1a reactive V beta 6+ or V beta 8.1+ T cells in responding cell populations. We found that nonstimulated CD8+ T cells produced a low amount of Mls-1a Ag, and the capacity to do so was considerably increased by stimulation with immobilized anti-TCR mAb. By contrast, nonstimulated CD4+ T cells did not produce Mls-1a Ag at all. Even when CD4+ T cells were activated via TCR signaling with immobilized anti-TCR mAb, CD4+ T cells did not produce Mls-1a Ag. However, CD4+ T cells primed with conventional Ag in vivo produced Mls-1a Ag on restimulation with that specific Ag in vitro. These findings indicate that not only CD8+ T cells but also CD4+ T cells can produce Mls-1a Ag on appropriate stimulation, although different mechanisms for Mls-1a production may operate between the CD4+ and CD8+ T cells.

Production of minor lymphocyte stimulatory-1a antigen from activated CD4+ or CD8+ T cells

Minor lymphocyte stimulatory (Mls) Ag are super Ag that stimulate a high proportion of T cells of a specific TCR V beta family. One of the super Ag, Mls-1a, which is recognized mainly by TCR V beta 6+ and V beta 8.1+ T cells, has recently been linked to the response to product of the open reading frame in 3'-long terminal repeat of endogenous mammary tumor virus, MTV-7. It is quite certain that B cells are able to produce and also to present the Mls-1a Ag. However, it remains to be determined whether other cell types, especially T cells, produce Mls-1a Ag. In this study using highly purified T cell subpopulations, capacity to produce Mls-1a Ag was analyzed by calculating the proportion of Mls-1a reactive V beta 6+ or V beta 8.1+ T cells in responding cell populations. We found that nonstimulated CD8+ T cells produced a low amount of Mls-1a Ag, and the capacity to do so was considerably increased by stimulation with immobilized anti-TCR mAb. By contrast, nonstimulated CD4+ T cells did not produce Mls-1a Ag at all. Even when CD4+ T cells were activated via TCR signaling with immobilized anti-TCR mAb, CD4+ T cells did not produce Mls-1a Ag. However, CD4+ T cells primed with conventional Ag in vivo produced Mls-1a Ag on restimulation with that specific Ag in vitro. These findings indicate that not only CD8+ T cells but also CD4+ T cells can produce Mls-1a Ag on appropriate stimulation, although different mechanisms for Mls-1a production may operate between the CD4+ and CD8+ T cells.

Influence of a small number of mature T cells in donor bone marrow inocula on reconstitution of lymphoid tissues and negative selection of a T cell repertoire in the recipient

Allo-chimerism and clonal elimination of self antigen (Ag) (Ia + Mls-1a) reactive V beta 6+ T cells were analyzed and compared between allogeneic bone marrow (BM) chimeras reconstituted with BM cells which had been treated with anti-Thy-1 monoclonal antibody (mAb) plus complement (C) (T- chimeras) and BM chimeras which had been reconstituted with BM cells pretreated with anti-Thy-1 mAb alone (T+ chimeras). When lethally irradiated AKR (Mls-1a) mice were reconstituted with BM cells from B10 or B10 H-2 congenic mice, both T+ and T- chimeras were entirely free of signs of graft-versus-host reaction (GVHR). However, complete replacement of the AKR lymphoid tissues by donor BM cells was accomplished at an early stage in T+ chimeras but not in T- chimeras. On the other hand, clonal elimination of V beta 6+ T cells reactive to the recipient Ag (Mls-1a) was abolished in T+ chimeras but successfully induced in T- chimeras. The V beta 6+ T cells not eliminated in T+ chimeras showed depressed responses against Mls-1a antigens. The findings herein demonstrate that T cells which contaminate a BM inoculum survive in recipient mice after treatment with anti-Thy-1 mAb without C in vitro followed by BMT. The surviving T cells have been estimated to represent fewer than 0.5% of the BM cells inoculated. These cells appear to accelerate the full replacement of recipient lymphoid tissues by donor cells. Furthermore, the T cells which survive in the marrow inoculum influence eventually the development of a tolerant state in the T cell repertoire of the donor.

Reconstitution of lymphoid tissues under the influence of a subclinical level of graft versus host reaction induced by bone marrow T cells or splenic T cell subsets

Reconstitution of lymphoid tissues under the influence of subclinical graft versus host reaction (GVHR) has been investigated. Lethally irradiated AKR mice were reconstituted with B10 bone marrow (BM) cells which had been treated with anti-Thy-1 antibody alone without complement (GVHR chimera). Their immunological reconstitution was analyzed and compared with that of AKR recipients which had been reconstituted with B10 BM cells treated with anti-Thy-1 antibody plus complement (control chimera). One hundred percent of both chimeras survived more than 100 days without showing clinical signs of GVHR. However, full donor chimerism was accomplished at an early stage after reconstitution in the former GVHR chimeras, whereas a substantial number of recipient T cells persisted in control chimeras for the entire observation period. When reconstitution of various lymphoid tissues was compared between control and GVHR chimeras, no difference in the reconstitution of the thymus and spleen was noted. By contrast, the cellularity of peripheral lymph nodes in GVHR chimeras was regularly considerably lower than that of the control chimeras. The apparent insufficiency of lymph node reconstitution appeared to be attributable to the impairment of lymph node structure itself which may be involved in lymphocyte homing. Furthermore, clonal deletion of V beta 6+ T cells which are reactive to recipient (Mls-1a) antigens was abrogated in the GVHR chimeras but was normally induced in the more completely T cell-depleted control chimeras. This abrogation of clonal deletion of V beta 6+ T cells appeared to result from the early disappearance of recipient T cells in these chimeras. Thus, it appeared that donor T cells in the BM that survive anti-Thy-1 treatment in vitro plus subsequent BM transplantation induced a subclinical level GVHR which contributed to the full donor chimerism as well as abrogation of clonal elimination of V beta 6+ donor T cells. Indeed, inoculation of CD8+ T cells along with the transplantation of the T cell-depleted BM cells (anti-Thy-1 plus C-treated cells) from donor mice into the AKR recipients was also shown to induce a similar state in the recipients.

Lymphokine-activated killer cell activity of CD4-CD8- TCR alpha beta + thymocytes

Functions of CD4-8-TCR alpha beta+ thymocytes, which are characterized by predominant usage of V beta 8.2 TCR, have remained unclear. In this study, we found that the CD4-8-TCR alpha beta + thymocytes expressed NK1.1 Ag and IL-2R beta-chain but not IL-2R alpha-chain. When the CD4-8- TCR alpha beta + thymocytes were cultured in the presence of IL-2, the CD4-8-TCR alpha beta + thymocytes vigorously proliferated. After 7 days of culture in the presence of 1000 U/ml of IL-2, approximately half of the CD4-8-TCR alpha beta + thymocytes lost NK1.1 Ag. However, the remaining half of the CD4-8-TCR alpha beta + cells showed increasing levels of NK1.1 Ag and acquired killer activity against tumor cells such as YAC-1, P815, and EL-4. These cells also killed syngeneic as well as allogeneic thymocytes. The LAK activity by the NK1.1+ CD4-8-TCR alpha beta + thymocytes was not inhibited by anti-NK1.1, anti-TCR alpha beta, or anti-CD44 mAb but was partially inhibited by anti-LFA-1 mAb. These findings indicate that the CD4-8-TCR alpha beta + thymocyte population can be divided into two population on the basis of NK1.1 expression after culture in the presence of IL-2. The NK1.1 Ag expression on the cultured CD4-8-TCR alpha beta + seems to be correlated to acquisition of LAK activity, although the NK1.1 Ag itself may not be directly involved in the target cell recognition. The present data suggest that the CD4-8- TCR alpha beta + thymocyte population is a functional T cell lineage which may serve as cells of immune defense and/or immune regulation.

Lymphokine-activated killer cell activity of CD4-CD8- TCR alpha beta + thymocytes

Functions of CD4-8-TCR alpha beta+ thymocytes, which are characterized by predominant usage of V beta 8.2 TCR, have remained unclear. In this study, we found that the CD4-8-TCR alpha beta + thymocytes expressed NK1.1 Ag and IL-2R beta-chain but not IL-2R alpha-chain. When the CD4-8- TCR alpha beta + thymocytes were cultured in the presence of IL-2, the CD4-8-TCR alpha beta + thymocytes vigorously proliferated. After 7 days of culture in the presence of 1000 U/ml of IL-2, approximately half of the CD4-8-TCR alpha beta + thymocytes lost NK1.1 Ag. However, the remaining half of the CD4-8-TCR alpha beta + cells showed increasing levels of NK1.1 Ag and acquired killer activity against tumor cells such as YAC-1, P815, and EL-4. These cells also killed syngeneic as well as allogeneic thymocytes. The LAK activity by the NK1.1+ CD4-8-TCR alpha beta + thymocytes was not inhibited by anti-NK1.1, anti-TCR alpha beta, or anti-CD44 mAb but was partially inhibited by anti-LFA-1 mAb. These findings indicate that the CD4-8-TCR alpha beta + thymocyte population can be divided into two population on the basis of NK1.1 expression after culture in the presence of IL-2. The NK1.1 Ag expression on the cultured CD4-8-TCR alpha beta + seems to be correlated to acquisition of LAK activity, although the NK1.1 Ag itself may not be directly involved in the target cell recognition. The present data suggest that the CD4-8- TCR alpha beta + thymocyte population is a functional T cell lineage which may serve as cells of immune defense and/or immune regulation.

NK1.1+ CD4+ CD8- thymocytes with specific lymphokine secretion

CD4+8- or CD4-8+ thymocytes have been regarded as direct progenitors of peripheral T cells. However, recently, we have found a novel NK1.1+ subpopulation with skewed T cell antigen receptor (TcR) V beta family among heat-stable antigen negative (HSA-) CD4+8- thymocytes. In the present study, we show that these NK1.1+ CD4+8- thymocytes, which represent a different lineage from the major NK1.1- CD4+8- thymocytes or CD4+ lymph node T cells, vigorously secrete interleukin (IL)-4 and interferon (IFN)-gamma upon stimulation with immobilized anti-TcR-alpha beta antibody. On the other hand, neither NK1.1- CD4+8- thymocytes nor CD4+ lymph node T cells produced substantial amounts of these lymphokines. A similar pattern of lymphokine secretion was observed with the NK1.1+ CD4+T cells obtained from bone marrow. The present findings elucidate the recent observations that HSA- CD4+8- thymocytes secrete a variety of lymphokines including IFN-gamma, IL-4, IL-5 and IL-10 before the CD4+8- thymocytes are exported from thymus. Our evidence indicates that NK1.1+ CD4+8- thymocytes are totally responsible for the specific lymphokine secretions observed in the HSA- CD4+8- thymocytes.

An NK1.1+ CD4+8- single-positive thymocyte subpopulation that expresses a highly skewed T-cell antigen receptor V beta family

In the present report we describe a CD4+8- heat stable antigen-negative (HSA-) thymocyte subpopulation that expresses a distinguishably low density of alpha beta T-cell antigen receptors (TCRlo) from the majority of CD4+8- high-density TCR (TCRhi) mature-type thymocytes. This subpopulation appears relatively late in life. Analysis of MEL-14, Pgp-1 (CD44), ICAM-1 (CD54), and NK1.1 expression on this subpopulation revealed that the CD4+8- TCRlo population was a population having unique characteristics (MEL-14-, CD44+, ICAM-1+, and NK1.1+) compared to the CD4+8- TCRhi thymocytes, most of which are MEL-14+, CD44-, ICAM-1-, and NK1.1-. When TCR beta-chain variable region (V beta) usage was analyzed, this thymic population expressed predominantly products of V beta 7 and V beta 8.2 TCR gene families. Interestingly, cells with V beta 8.1 TCRs, which are reactive to Mls-1a antigens, were not eliminated from the CD4+8- HSA- TCRlo subpopulation but had been eliminated from the major CD4+8- HSA- TCRhi subpopulation in Mls-1a strains. A subset with a phenotype similar to the CD4+8- HSA- TCRlo thymocytes was also identified primarily in bone marrow, and this subset constituted approximately half of the CD4+ T cells in the bone marrow. The CD4+8- HSA- TCRlo cells showed extremely high proliferative responses to immobilized anti-TCR antibody but generated negligible responses to allogeneic H-2 antigens compared to the responses generated by the major CD4+8- HSA- CD3hi cells. However, the CD4+8- HSA- TCRlo cells in Mls-1b mice mounted vigorous proliferative responses to Mls-1a antigens but not in Mls-1a mice. The properties of this T-cell subset suggest that these cells belong to a lineage distinct from the major T-cell population.

Clonal elimination of self reactive V beta 6+ T cells induced by H-2 products expressed on thymic radio-resistant components

The role of thymic radio-resistant cells on clonal elimination of V beta 6+ T cells that are reactive to minor lymphocyte stimulatory (Mls)-1a plus I-E antigens has been investigated. Previous studies with allogeneic bone marrow chimeras revealed that radio-sensitive I-E+ cells derived from donor bone marrow in the thymus play a major role in the clonal elimination of V beta 6+ T cells. However, we could show that not only the thymic bone marrow derived components but also the radio-resistant ones (presumably thymic epithelial cells) might be involved in induction of clonal elimination of the self-reactive T cells. The proportion of V beta 6+ T cells present varied with the H-2 haplotype of the thymus and the cell types presenting Mls-1a products, which might be attributable to differences in the affinity of the H-2 products to T cell antigen receptors and differences in the amount of tolerogens expressed on the stromal cells.

Deficiency in early development of the thymus-dependent cells in irradiation chimeras attributable to recipient's environment

Allogeneic bone marrow chimeras were prepared using reciprocal combinations of AKR and C3H mice. When C3H mice were recipients, the number of thymocytes recoverable from such chimeras (C3H recipient chimeras) was small as compared with that from chimeras for which AKR mice were used as recipients (AKR recipient chimeras) regardless of donor strain. The thymocytes from C3H recipient chimeras showed a profound deficiency in generating proliferative responses to stimulation by anti-CD3 mAb (2C11) or anti-TCR (alpha, beta) mAb (H57-597), even though the expression of CD3 and TCR molecules fell within the same range as that in AKR recipient chimeras. Furthermore, after stimulation with immobilized 2C11, the proportion of IL-2R+ cells in the thymocytes from C3H recipient chimeras was much less than that in AKR recipient chimeras. However, no significant difference in proliferative responses to 2C11 plus PMA, in influx of Ca2+ after stimulation with 2C11 or IL-2 production in response to 2C11 plus PMA or PMA plus A23187 was demonstrated between C3H and AKR recipient chimeras. These findings suggest that the thymocytes from C3H recipient chimeras have a deficiency in the signal transduction system as compared with chimeras for which AKR mice are the recipients. The thymic stromal component involved in this difference in the C3H recipient chimeras is discussed.

Deficiency in early development of the thymus-dependent cells in irradiation chimeras attributable to recipient's environment

Allogeneic bone marrow chimeras were prepared using reciprocal combinations of AKR and C3H mice. When C3H mice were recipients, the number of thymocytes recoverable from such chimeras (C3H recipient chimeras) was small as compared with that from chimeras for which AKR mice were used as recipients (AKR recipient chimeras) regardless of donor strain. The thymocytes from C3H recipient chimeras showed a profound deficiency in generating proliferative responses to stimulation by anti-CD3 mAb (2C11) or anti-TCR (alpha, beta) mAb (H57-597), even though the expression of CD3 and TCR molecules fell within the same range as that in AKR recipient chimeras. Furthermore, after stimulation with immobilized 2C11, the proportion of IL-2R+ cells in the thymocytes from C3H recipient chimeras was much less than that in AKR recipient chimeras. However, no significant difference in proliferative responses to 2C11 plus PMA, in influx of Ca2+ after stimulation with 2C11 or IL-2 production in response to 2C11 plus PMA or PMA plus A23187 was demonstrated between C3H and AKR recipient chimeras. These findings suggest that the thymocytes from C3H recipient chimeras have a deficiency in the signal transduction system as compared with chimeras for which AKR mice are the recipients. The thymic stromal component involved in this difference in the C3H recipient chimeras is discussed.

Thymus: a direct target tissue in graft-versus-host reaction after allogeneic bone marrow transplantation that results in abrogation of induction of self-tolerance

Graft-versus-host reaction (GVHR) following allogeneic bone marrow (BM) transplantation was investigated by analyzing expression of antigen receptors on T cells specific for recipient antigens. GVHR chimeras were prepared by transplanting mixtures of splenic T cells and T-cell-depleted BM cells from B10 (I-E-, Mls-1b) or B10.AQR (I-E+, Mls-1b) mice into lethally irradiated AKR/J (I-E+, Mls-1a) recipients. Increased proportions of V beta 6+ T cells reactive to recipient antigens (I-E and Mls-1a) were observed in thymuses from such chimeras 1 or 5 wk after BM transplantation. V beta 6+ T cells observed 1 wk after BM transplantation were derived from mature T cells that had been inoculated into recipients. These cells responded to recipient antigens expressed in the thymus. After 5 wk, thymocytes brightly positive for V beta 6+ were shown not to descend from mature T cells but to differentiate from precursor cells present in the BM inocula. Since V beta 6+ T cells were eliminated in thymuses from non-GVHR chimeras 5 wk after BM transplantation using T-cell-depleted BM cells alone, it appears that GVHR occurring in the thymus at an early stage abrogates thymic stromal functions essential to induction of self-tolerance in the T-cell repertoire. These findings propose a mechanism (autoimmunity) to explain in part the pathogenesis of chronic GVHR.

Cell components required for deletion of an autoreactive T cell repertoire

T cells become tolerant to self antigens during their development in the thymus. Clonal deletion of thymocytes bearing T cell receptor (TcR) which recognize self antigens is a major mechanism for generating tolerance. In the present study we have used allogeneic bone marrow (BM) chimeras, prepared with various combinations of mouse strains and focusing especially on expressions of I-E molecules and Mls-1a antigens on the cell surface, to investigate both immunohistochemically and by flow cytometry the cell components that contribute to the clonal deletion of T cells positive for V beta 6 TcR. The V beta 6 TcR expression is strongly associated with T cell recognition of both I-E and Mls-1a antigens. We found that I-E+ cells derived from donor BM (and thus not of recipient lineage) represented a primary requirement for deletion of Mls-1a-reactive thymocytes which bear V beta 6 TcR. Immunohistochemical analysis revealed that the donor-derived I-E+ cells were distributed mainly to the thymic medulla and that the V beta 6+ cells were eliminated from the thymic medulla between 2 and 3 weeks following BM transplantation. In contrast, Mls-1a+ cells of either donor or recipient origin might be responsible for the deletion, even though cortical epithelial cells appeared not to express Mls-1a antigens.

Sequential analysis of the thymocyte differentiation in fully allogeneic bone marrow chimera in mice. II. Further characterization of the CD4+ or CD8+ single positive thymocytes

Differentiation of CD4+8- and CD4-8+ single-positive (SP) thymocytes in fully allogeneic bone marrow chimeras were investigated using multicolor cytometric analysis. The proportion of CD3+ cells in CD4+ SP population derived from donor mice considerably increased between day 12 and 14 after bone marrow transplantation (BMT), and gradually increased thereafter. The proportion of V beta 8+ cells in the CD3+CD4+ population remained constant (around 20%) at each period, suggesting that alpha and beta chains were used as TCR. The proportion of J11d+ cells in the CD4+ SP thymocytes transiently increased from day 12 to 14 and decreased thereafter, even though almost half of CD4+ SP cells were still dull J11d+ at day 35 after BMT. When CD8+ SP populations were analyzed, the proportion of CD3+ cells was very small until day 18. Thereafter, the proportion considerably increased and reached a maximum (83.2%) at day 21. The proportion of V beta 8+ cells in the CD3+ CD8+ SP population fell within range between 20 and 30%. However, before day 18, most of the V beta 8+ cells were dull positive, while after day 21 the majority were bright V beta 8+. Further, CD8+ SP cells at day 12, 14 and 18 were largely bright J11d+. After day 21, however, the proportion of bright J11d+ cells rapidly decreased. Similar results were obtained when the sequence of appearance of CD4+ and CD8+ SP cells was compared among bright CD3+, bright V beta 8+ or J11d- mature populations. The CD4+ SP cells regularly appeared earlier than CD8+ SP cells in the mature populations. These findings indicate that a considerable heterogeneity exists within both CD4+ and CD8+ SP populations and that the differentiation process for CD4+ SP cells precedes that for CD8+ SP cells.

Sequential analysis of the thymocyte differentiation in fully allogeneic bone marrow chimera in mice. I. Relationship between functions and surface characteristics of thymocytes

Differentiation of thymocytes according to surface phenotype, functional status and cell size was investigated using fully allogeneic bone marrow chimeras. Most of the donor-derived thymocytes obtained from chimeras 9 days after hematopoietic reconstitution were CD4-8- and IL2R+. At day 14, CD4+8+ cells became prominent in the thymus. Eighty-six per cent of thymocytes were CD4+8+ and 9% were CD4-8- at this stage. After day 21, the proportion of CD4+8- or CD4-8+ single positive cells transiently increased and then declined to normal level at day 42. Further, the mean size of CD4+ or CD8+ single positive cells in chimeric thymuses at day 21 after reconstitution was markedly larger than that at day 35. When proliferative responses to various stimuli (PMA + rIL2, anti-CD3 mAb (2C11) and anti-V beta 8 mAb (F23.1] were evaluated, significant responses were generated by thymocytes for the first time at around day 28 and the responses reached their peaks at day 35. These findings demonstrated that the process of thymocyte differentiation in the fully allogeneic chimeras was similar to ontogenic development as observed in fetal mice. However, the tempo at which the differentiation of surface phenotypes and development of functions proceeded was quite different from that seen in normal mice. The relationship among surface phenotypes, cell size and functions of developing thymocytes of bone marrow chimeras is discussed.