Generation and regulation of autocytotoxicity in mixed lymphocyte cultures: evidence for active suppression of autocytotoxic cells

Corticosterone inhibits GAS6 to govern hair follicle stem-cell quiescence

Chronic, sustained exposure to stressors can profoundly affect tissue homeostasis, although the mechanisms by which these changes occur are largely unknown. Here we report that the stress hormone corticosterone-which is derived from the adrenal gland and is the rodent equivalent of cortisol in humans-regulates hair follicle stem cell (HFSC) quiescence and hair growth in mice. In the absence of systemic corticosterone, HFSCs enter substantially more rounds of the regeneration cycle throughout life. Conversely, under chronic stress, increased levels of corticosterone prolong HFSC quiescence and maintain hair follicles in an extended resting phase. Mechanistically, corticosterone acts on the dermal papillae to suppress the expression of Gas6, a gene that encodes the secreted factor growth arrest specific 6. Restoring Gas6 expression overcomes the stress-induced inhibition of HFSC activation and hair growth. Our work identifies corticosterone as a systemic inhibitor of HFSC activity through its effect on the niche, and demonstrates that the removal of such inhibition drives HFSCs into frequent regeneration cycles, with no observable defects in the long-term.

CD8high (CD57+) T cells in normal, healthy individuals specifically suppress the generation of cytotoxic T lymphocytes to Epstein-Barr virus-transformed B cell lines

We have previously identified two subsets of CD8+, CD57+ lymphocytes in normal peripheral blood: i) T cells expressing high levels [CD8high(CD57+)] and ii) natural killer cells expressing low levels of surface CD8[CD8low(CD57+)]. We investigated the cytotoxic and suppressive function of CD8high(CD57+) T lymphocytes from normal, healthy individuals using standard chromium-release assays and limiting dilution analysis. In normal, healthy subjects, this cell subset suppressed the generation of cytotoxic T lymphocytes (CTL) to autologous, Epstein-Barr virus (EBV)-transformed B cell lines (BCL). Depletion of CD8high(CD57+) T lymphocytes from peripheral blood mononuclear cells (PBMC) resulted in a three- to sevenfold rise in CTL precursor frequency to autologous EBV-transformed BCL, but not allogeneic PBMC or BCL by LDA. Replacement of CD8high(CD57+) T lymphocytes in limiting dilution cultures led to the dose-dependent suppression of EBV-specific, but not allogeneic, CTL generation. Supernatant from CD8high(CD57+) T lymphocytes cultured with autologous BCL did not exhibit suppression, suggesting that soluble factors were not responsible. As CD8high(CD57+) T lymphocytes did not, themselves, exhibit cytotoxicity against autologous BCL, removal of BCL stimulator cells in co-culture was not the mechanism of suppression. Furthermore, while the CD8high(CD57+) T lymphocytes from healthy subjects suppressed the generation of CTL to autologous BCL, they did not suppress the cytotoxic activity of established mixed lymphocyte reactions or peptide-specific CTL clones, as has been reported in bone marrow transplant recipients and human immunodeficiency virus patients. This suggests that CD8high(CD57+) T lymphocytes from healthy subjects suppress the generation of, rather than killing by, CTL in a contact-dependent manner. To our knowledge, this is the first identification of a phenotypically distinct subset of human CD8+ T cells that can suppress generation of antigen-specific major histocompatibility complex class I-restricted CTL.

Activated, cytotoxic lymphocytes in systemic vasculitis

Peripheral blood lymphocytes from some patients with rheumatoid vasculitis and giant cell arteritis were cytotoxic in vitro towards endothelial cells, but not fibroblasts. Use of cell surface markers and cell density showed that cytotoxicity correlated with numbers of HLA-DR bearing cells, but not with cells bearing CD3, the transferrin receptor, or less dense lymphocytes. We concluded that activated, cytotoxic lymphocytes were present in the peripheral blood of a sub-set of patients with vasculitis.

Limiting-dilution analysis of the HLA restriction of anti-Epstein-Barr virus-specific cytolytic T lymphocytes

Human Epstein-Barr virus (EBV) specific cytotoxic T lymphocytes (CTL) play an important role in maintaining the virus/host equilibrium during persistent infections. We analysed precursors of anti-EBV CTL by the limiting-dilution technique. Seven healthy EBV-seropositive and two EBV-seronegative donors were tested. All the donors seropositive for EBV gave clear-cut positive results, and it was remarkable that the frequency of CTL precursors (CTLp) observed was much higher than that reported for other viruses. In contrast, in the seronegative donors the frequency of CTLp was undetectable. The CTLp were derived from the CD4-CD8+ population only, although EBV-specific CD4+ cytolytic T cell clones have been described. A study of the HLA restriction showed that some HLA-A or HLA-B antigens can function as preferential restricting molecules, but that CTLp restricted by the other HLA-A or HLA-B molecules also exist. However, the dominant population of CTL present in primary responses is sometimes different from that of long term cell lines established from the same donor.

Antierythrocyte autoantibody formation after therapy with interleukin-2 and gamma-interferon

The cardiovascular, renal, pulmonary, and dermatologic toxicities of interleukin-2 (IL-2) and gamma-interferon (IFN) are well described. However, autoimmune toxicities have only recently been noticed. The authors report the development of warm autoantibodies against erythrocytes in a patient receiving IL-2 (3.75 x 10(6) cetus units/m2 intravenous bolus three times per week) and gamma-IFN (0.1 mg/m2 subcutaneously three times per week) for metastatic renal cell carcinoma. Other potential causes of autoantibody formation, such as drugs, infection, and collagen vascular disease, were excluded. Both gamma-IFN and IL-2 have the potential to trigger or exacerbate autoimmunity due to either aberrant expression of restricted antigens or inhibition of normal cellular immune suppressor mechanisms.

Cytotoxic T lymphocytes reactive against a syngeneic murine tumor and their specific suppressor T cells are both elicited by in vitro allosensitization

Sensitization of C57BL/6 (B6, H-2b) splenocytes against normal BALB/c (H-2d) leukocytes (B6 a/BALB) in bulk MLC induced CTL reactive against the syngeneic (H-2b) nonimmunogenic lymphoma PIR-2, in addition to the CTL directed against the corresponding (H-2d) allotargets. However, MLC-derived lymphocytes did not directly exhibit anti-PIR-2 cytotoxicity in spite of the high anti-PIR-2 CTL frequency (up to 1/20) among them, as demonstrated by the limiting dilution culture (LDC) technique. The present study was undertaken to resolve this contradiction. We found that anti-PIR-2 cytotoxicity could be detected only when B6 a/BALB MLC-derived responding cells were plated in LDC at low numbers (less than 200) of cells/well. In contrast, increasing the number of the plated cells to 500-5,000 resulted in a gradual decrease in the percentage of wells cytotoxically reactive against PIR-2, whereas the percentage of wells exhibiting cytotoxicity against the allotargets remained unchanged (100%). This decrease of anti-PIR-2 cytotoxicity in LDC and the lack of anti-PIR-2 reactivity among MLC-derived lymphocytes were shown by mixing experiments to result from the activity of radioresistant Thy-1+, Lyt-2+, L3T4- suppressor cells, blocking the anti-PIR-2 cytotoxicity at the effector phase. The suppression was specific as indicated by the following observations: (a) freshly obtained B6 splenocytes, cultured unsensitized B6 splenocytes, mitogen-induced B6 lymphoblasts, B6 LAK cells, or B6 a/B6 MLC-derived lymphocytes were not suppressive; (b) anti-PIR-2 cytotoxicity elicited in B6 a/BALB LDC was suppressed only by lymphocytes derived from B6 a/BALB MLC and not from B6 a/C3H (H-2k) MLC; and (c) B6 a/BALB MLC-induced suppressor cells could be adsorbed on monolayers of BALB/c but not of C3H lymphoblasts. Since both syngeneic tumor and allogeneic target cells were lysed by the same clonal cell population but only the antisyngeneic activity was suppressed, we suggest that a single CTL can exhibit two cytotoxic activities that are differentially affected by the described suppressor cells. This mode of suppression may play a role in controlling autoimmune reactivity.

Differential expression and regulation of the human CD8 alpha and CD8 beta chains

The CD8 glycoprotein is expressed by thymocytes, mature T cells and natural killer (NK) cells and has been implicated in the recognition of monomorphic determinants on major histocompatibility complex (MHC) Class I antigens, and in signal transduction during the course of T-cell activation. Both human and rodent CD8 antigens are comprised of two distinct polypeptide chains, alpha and beta. The majority of monoclonal antibodies (mAb) reactive with the human CD8 antigen bind the CD8 alpha chain, while a single mAb, T8/2T8-5H7, has been identified which binds to the CD8 alpha/beta heterodimer. While the two chains of CD8 have been presumed to be coordinately expressed in normal T cells, this is not always the case. Northern blot analysis of a panel of T-cell leukemias and normal cells demonstrate that CD8 alpha and CD8 beta are not invariably co-transcribed and phenotypic analysis of fresh and interleukin 2 (IL-2) expanded peripheral blood mononuclear cells (PBMC) confirm that the CD8 alpha and CD8 beta chains are differentially expressed at the cell surface. Four distinct subpopulations of CD8+ cells have been identified based on the expression of CD8 alpha/alpha or CD8 alpha/beta complexes: (1) T-cell receptor (TcR) alpha beta+ T cells which are CD8 alpha+/beta+; (2) TcR alpha beta+ T cells which are CD8 alpha+/beta-; (3) TcR gamma delta+ T cells which are CD8 alpha+/beta- and (4) natural killer (NK) cells which are CD8 alpha+/beta-. We also demonstrate the down-regulation of the CD8 alpha/beta heterodimers from the surface of a CD8+ T-cell clone following treatment with phorbol myristate acetate (PMA) while CD8 alpha/alpha homodimers remain on the cell surface. This observation demonstrates that a) a CD8+ T-cell clone can express both CD8 alpha/alpha homodimers and CD8 alpha/beta heterodimers and b) these two complexes do not have identical biological properties. Together, these data suggest that CD8 alpha/alpha and CD8 alpha/beta dimers may not subserve identical functions. The differential contribution of these two CD8 complexes should be considered in models of T-cell-mediated cytotoxicity and T-cell activation.

MHC class II restricted self-recognition after allostimulation: clonal analysis

After allostimulation in vitro using a combination of HLA-A, B, C, DR, DQ, D identical but HLA-DP different homozygous typing cells, 34 T cell clones were derived. Thirty-one of them were alloreactive clones, but three clones were found to be autoreactive. One of these autoreactive clones was further expanded. In order to characterize in more detail the determinant restricting the autologous response, a panel of HLA-typed peripheral blood mononuclear cells (PBMC) or Epstein-Barr virus lymphoblastoid cell lines (EVB-LCL) was typed. A good correlation of typing responses with the self haplotype HLA-A1, B8, Cw7, DR3, DRw52, DQw2 was found. Typing responses also segregated together with this haplotype in informative families. Blocking studies using MHC class I and II specific monoclonal antibodies (MoAb) linked the restricting determinant to MHC class II molecules. The clone which was both autoproliferative and autocytotoxic bore the CD3(+), CD4(+), CD8(-), Ia(+) phenotype. Antibiotics or foreign plasma proteins were ruled out as restricted determinants.

Specific helper T cell reactivity against autologous erythrocytes implies that self tolerance need not depend on clonal deletion

Using a culture system which supports primary T cell proliferative responses to various antigens we have detected mouse red blood cell (RBC)-reactive T cells in lymphoid tissues from untreated mice. The release of significant amounts of interleukin 2 (IL2) indicates that T helper (or helper/inducer) cells are activated by stimulation with RBC. Upon restimulation in vitro these cells proliferate specifically against mouse RBC with the kinetics and magnitude characteristic of a secondary response. Since autologous RBC are tolerated in vivo in spite of the presence of such specifically reactive T helper cells, these findings imply that self tolerance, even to certain nonsequestered antigens, may depend largely on regulatory mechanisms rather than on clonal deletion or inactivation.

T lymphocyte control of autoreactivity: analysis with human T cell clones and limiting dilution culture

To investigate cellular mechanisms controlling activated autoreactive T lymphocytes, a limiting dilution system was established employing cloned autoreactive major histocompatibility complex class II specific lymphocytes (a2/7) as stimulator cells for autologous peripheral blood mononuclear cells. At low responder/stimulator ratios, cytotoxic effector cells were generated capable of lysing clone a2/7. Importantly, within the population of cells mediating autocytotoxic effector function, differential specificities were found to exist. The generation of such autocytotoxic T lymphocytes appears to be inhibited by an additional population of cells circulating at lower frequency suggesting that autoreactivity is controlled at distinct levels by discrete functional cellular subsets.