Maximal proliferation of cytotoxic T lymphocytes requires reverse signaling through Fas ligand.

Fas ligand (FasL/CD95L) is best known for its role in delivering apoptotic signals through its receptor, Fas (APO-1/CD95). In this study, we present evidence that FasL has a second role as a signaling receptor. Alloantigen-specific proliferation by multiple FasL- murine CTL lines is depressed compared to that of FasL+ CTL lines. FasL- CTLs kill efficiently on a per recovered cell basis and can achieve wild-type levels of proliferation upon stimulation by optimal doses of anti-CD3, suggesting the lack of a costimulatory signal during antigen stimulation. To test this hypothesis directly, soluble FasIgG, a fusion protein of murine Fas and human IgG1, was added to FasL+ CTLs to demonstrate that blocking cell surface Fas-FasL interactions mimics the depression observed for FasL- CTLs. In addition, plate-bound FasIgG in conjunction with suboptimal anti-CD3 stimulation augments proliferative signals in FasL+ but not FasL- CTLs. In contrast to these results with CD8+ T cells, alloantigen-stimulated FasL- CD4+ T cells proliferate vigorously compared to FasL+ cells. These data demonstrate that reverse signaling through FasL is required for CTLs to achieve maximal proliferation and may provide clues to differences in the homeostatic regulation of activated CD4+ and CD8+ T cells during an immune response.

H-2 antigens of the thymus determine lymphocyte specificity.

After immunization, normal H-2 heterozygous mice (for example H-2(b) x H-2(d)) generate two populations of cytotoxic effector T cells, one specific for target cells expressing H-2(b)-plus-antigen and the other specific for H- 2(d)-plus-antigen. With a multideterminant antigen, these two populations have about the same activity. We show here that the H-2 type of resident cells in the thymus determines the H-2 preference of cytotoxic T lymphocytes. F(1)(B 10 x B 10.D2) (H-2(b) x H-2 (d)) mice were thymectomized, lethally irradiated, and reconstituted with T-cell-depleted syngeneic hematopoietic cells. Groups of such ATXBM mice were grafted subcutaneously with neonatal thymus lobes from parental mice, either B10 (H-2 (b)) or B10.D2 (H-2(d)). 2-3 mo later, the mice were immunized against the minor histocompatibility antigens on F(1)(BALB/c x BALB.B) cells and assayed for cytotoxic T-cell activity. H-2(b) x H-2(d) ATXBM mice with H-2(b) thymus grafts responded to antigen-plus-H-2(b) much better than to antigen-plus-H-2(d), and vice versa for the mice with H-2(d) thymus grafts. As judged by antiserum treatment, the effector cells were of F(1) origin. To explore the possibility that the "thymus preference" may have been due to suppression of T-cell activity, nonimmune spleen and lymph node cells from normal H-2(b) x H-2(d) mice and cells from H-2(b) x H-2(d) mice bearing a homozygous thymus were mixed 1:1 and immunized in adoptive transfer. The mixture responded to antigen-plus-H-2(b) and antigen-plus-H-2(d) equally well, demonstrating that the cells that showed a "thymus preference" could not suppress a response to antigen in association with the nonthymic H-2 type. We conclude from these and other experiments that H-2 antigens present on resident cells of the thymus determine the spectrum of specificity of T cells which mature in that thymus and eventually make up the peripheral T- cell pool.

Haplotype-specific suppression of cytotoxic T cell induction by antigen inappropriately presented on T cells.

To detect a strong cytotoxic T lymphocyte (CTL) response to minor histocompatibility (H) antigens in a 5-d mixed lymphocyte culture, it is necessary to use a responder that has been primed in vivo with antigen-bearing cells. It has previously been shown that minor-H-specific CTL can be primed in vivo both directly by foreign spleen cells and by presentation of foreign minor H antigens on host antigen-presenting cells. This latter route is evident in the phenomenon of cross-priming, in which H-2 heterozygous (A x B)F1 mice injected 2 wk previously with minor H-different H-2A (A') spleen cells generate both H-2A- and H-2B-restricted minor-H-specific CTL. In a study of the kinetics of direct- vs. cross-priming to minors in F1 mice, we have found that minor H-different T cells actually suppress the induction of virgin CTL capable of recognizing them. CTL activity measured from F1 mice 3-6 d after injection with viable A' spleen cells is largely H-2B restricted. The H-2A-restricted response recovers such that roughly equal A- and B-restricted activity is detected in mice as early as 8-10 d postinjection. This temporary hyporeactivity does not result from generalized immunosuppression--it is specific for those CTL that recognize the foreign minor H antigen in the context of the H-2 antigens on the injected spleen cells. The injected spleen cells that mediate this suppression are radiosensitive T cells; Lyt-2+ T cells are highly efficient at suppressing the induction of CTL in vivo. No graft vs. host reaction by the injected T cells appears to be required, as suppression of direct primed CTL can be mediated by spleen cells that are wholly tolerant of both host H-2 and minor H antigens. Suppression cannot be demonstrated by in vitro mixing experiments. Several possible mechanisms for haplotype-specific suppression are discussed, including inactivation of responding CTL by veto cells and in vivo sequestration of responding CTL by the injected spleen cells.

Thymic cytotoxic T lymphocytes are primed in vivo to minor histocompatibility antigens.

Potent cytotoxic T lymphocyte (CTL) activity can be derived from cultures of thymocyte responders and minor H different spleen cell stimulators. As is the case of the spleen cell response previously reported, this cytotoxic activity requires in vivo priming. We performed several experiments designed to determine whether the in vivo priming effect is due to the in situ priming of the thymocyte CTL precursors, to contamination of thymus cell preparations with cells of neighboring lymph nodes, or to the appearance in the thymus of antigen-reactive peripheral T cells. We show by depletion of peripheral cells with antilymphocyte serum and part body irradiation that recent thymic immigrants derived from the bone marrow contribute to the primed thymic response. Thymic CTL were primed in animals in which peripheral T cell responses were completely eliminated by repeated treatment in vivo with monoclonal anti-Thy-1 reagents. Primed, antigen-activated lymph node cells were also demonstrated to contribute to the thymus-derived CTL response. Thus, the minor H-specific thymic CTL response is due both to in situ priming and the immigration of activated peripheral T cells. We discuss the possible significance for models of T cell differentiation of the presence within the thymus of antigen and antigen-reactive mature T cells.

Generation of diversity in T cell receptor repertoire specific for pigeon cytochrome c.

17 T cell clones and 3 T cell lines, specific for pigeon cytochrome c, were analyzed for fine specificity and rearranged T cell receptor (TCR) gene elements. Clones of similar fine specificities were grouped into one of four phenotypes, and correlations between phenotype differences and gene usage could be made. All the lines and clones rearranged a member of the V alpha 2B4 gene family to a limited number of J alpha regions. The beta chain was made up of one of three non-cross-hybridizing V beta regions, each rearranging to only one or two J beta s. The use of alternate V beta regions could be correlated with phenotype differences, which were manifested either as MHC- or MHC and antigen-specificity changes. In addition, the presence of alloreactivity, which defined a phenotype difference, could be correlated solely with the use of an alternate J alpha region. These observations were substantiated by prospective analyses of pigeon cytochrome c-specific T cell lines that were selected for alternate MHC specificity or alloreactivity and were found to express the correlated alpha and beta chain rearrangements. Previously, the TCR DNA sequences from two clones, each representing a variant of one phenotype, showed sequence differences only in the N regions of their TCR genes. Since only these two variants, using identical V alpha-J alpha and V beta-J beta gene elements, were repeatedly observed in this study, we would predict that the junctional diversity differences are selectable. In this T cell response, all the gene elements involved in the generation of diversity appear to be selected, and may therefore be important in the determination of TCR specificity. This high degree of receptor gene selection represents a fundamental difference from the diversity seen in several extensively analyzed antibody responses.

Both intrathymic and peripheral selection modulate the differential expression of V beta 5 among CD4+ and CD8+ T cells.

Murine T cells expressing V beta 5 are characterized by (a) intrathymic deletion in the presence of I-E and products of endogenous mouse mammary tumor viruses, and (b) a greater representation in CD8+ relative to CD4+ peripheral T cells, thought to be due to more efficient intrathymic positive selection on class I rather than class II major histocompatibility complex antigens. We have engineered mice that are transgenic for a rearranged gene encoding a V beta 5+ beta chain of the T cell receptor for antigen. Deletion is not predicted in I-E- V beta 5+ transgenic mice, and until the age of 2 wk, the CD4/CD8 ratio of peripheral T cells is > 3:1 and indistinguishable between transgenic and nontransgenic mice. Transgenic mice then show a rapid, age-dependent decline in the ratio of CD4+ to CD8+ T cells in the lymphoid periphery, reaching a low of 1:10 by 7 mo of age. Furthermore, the percent of peripheral CD4+ cells that express the transgene drops with age, reaching a low of about 60% at 7 mo, while the percent of CD8+ cells that express V beta 5 remains greater than 95% at all ages. The lymphoid periphery is implicated in this selection against CD4+ V beta 5+ T cells as it occurs more rapidly in thymectomized transgenic mice, and can be delayed in mice whose peripheral T cells are replaced by recent thymic emigrants after depletion by in vivo treatment with anti-Thy-1 antibodies. These results indicate that the relative expression of V beta 5 in T cell subsets can be influenced not only intrathymically in I-E+ V beta 5+ transgenic mice, but also by events in the periphery, in the absence of I-E expression.

Molecular analysis of the influences of positive selection, tolerance induction, and antigen presentation on the T cell receptor repertoire.

Immunization of both B10.A and B10.S(9R) mice with pigeon cytochrome c (pcc) elicits T cells capable of proliferating to pcc presented on I-E major histocompatibility complex (MHC) molecules. The T cell receptor (TCR) repertoire used by pcc-specific T cells from these two strains is markedly different, even for T cells recognizing very similar antigen/MHC complexes. Our current studies have been directed toward explaining this differential expression between MHC congenic strains of TCR gene elements capable of recognizing similar ligands. Analysis of the TCR repertoire of pcc-specific T cells from F1[B10.A x B10.S (9R)]----parent radiation chimeras has demonstrated that much of this difference is a result of the positive selection of T cells for MHC restriction specificity. Further analysis of T cell lines from F1 mice and from radiation chimeras stimulated in vitro with pcc on both B10.A and B10.S(9R) antigen-presenting cells has provided clear-cut examples of the influence of positive selection, tolerance induction and of both in vivo and in vitro antigen presentation on the shaping of the TCR repertoire for a protein antigen. This is the first molecular analysis of how positive selection, tolerance induction, and antigen presentation can combine to mold the TCR repertoire.

Selection of amino acid sequences in the beta chain of the T cell antigen receptor.

The induction of an immune response in mammals is initiated by specifically reactive T lymphocytes. The specificity of the reaction is mediated by a complex receptor, part of which is highly variable in sequence and analogous to immunoglobulin heavy- and light-chain variable domains. The functional specificity of the T cell antigen receptor is, however, markedly different from immunoglobulins in that it mediates cell-cell interactions via the simultaneous recognition of foreign antigens and major histocompatibility complex-encoded molecules expressed on the surface of various lymphoid and nonlymphoid cells. The relation between the structure of the receptor and its functional specificity was investigated by analyzing the primary sequences of the receptors expressed by a series of T lymphocyte clones specific for a model antigen, pigeon cytochrome c. Within this set of T lymphocyte clones there was a striking selection for amino acid sequences in the receptor beta-chain in the region analogous to the third complementarity-determining region of immunoglobulins. Thus, despite the functional differences between T cell antigen receptors and immunoglobulin molecules, analogous regions appear to be important in determining ligand specificity.

The relationship of psychiatry to primary care.

Although it is not officially considered a primary care specialty, psychiatry is intimately related to training and practice in fields that are so designated. The primary care physician must have expertise in interviewing, counseling, psychophysiological disease, dependence syndromes, etc.--all areas in which psychiatry has a body of knowledge and intervention techniques. It is recommended that all primary care training programs develop behavioral objectives in the areas of mental illness and psychosocial aspects of disease; active liaison and consultation with departments of psychiatry should be an integral part of these programs. The author presents suggestions for possible program design and notes that the relationship between psychiatry and primary care specialties is a continuing challenge to the field.

Whatever happened to psychiatry? The deprofessionalization of community mental health centers.

The authors describe the dichotomy in the concept of community mental health centers. One view regards the community mental health center as a service provider for underserved populations, and another holds that it is an agent of social change. Deprofessionalization of community mental health centers has resulted from this lack of clear purpose, curtailment of funds, and conflicts over authority, service delivery, and control of the centers. Deprofessionalization has led to a decline in the number of psychiatrists in community mental health centers and a potentially negative impact on the quality of patient care.

A modest proposal for consultation/liaison psychiatry in the 1980s.

The authors discuss how consultation/liaison psychiatry has promoted closer cooperation between primary care and psychiatry in the general hospital setting and has increased physician concern for psychosocial issues while at the same time creating financial and organizational problems for consultation/liaison programs. To remedy these difficulties, the authors propose that all general hospitals that have more than 350 beds have fully staffed consultation/liaison services and that these services be funded through third-party reimbursement formulas as an integral hospital-based service. They outline six potential benefits of their proposal and suggest that action must be taken now if consultation/liaison psychiatry is not to suffer the same fate as the community mental health center movement.

Board certification anxiety.

The authors discuss how stress influences the candidate's capacity to effectively prepare for and fully demonstrate his or her abilities in the oral examination in psychiatry given by the American Board of Psychiatry and Neurology. They highlight subtle misconceptions about examiner priorities, attitudes, and evaluation methods and note common errors that reflect both anxiety and these misconceptions. They offer some advice and information to aid the candidate in coping with these examination difficulties.

The influence of MHC gene products on the generation of an antigen-specific T-cell repertoire.

We have previously described the B10.A pigeon cytochrome c-specific response in terms of clonal phenotypes and T-cell receptor (TcR) gene usage. All B10.A T-cell clones studied respond to antigen in association with syngeneic B10.A APCs and cross-react to antigen in association with one or two allogeneic variants of the I-E-encoded MHC molecules. In congenic strains of mice expressing these allogeneic MHC alleles [B10.A(5R) and B10.S(9R)], pigeon cytochrome c-specific T cells exhibit very similar MHC cross-reactivities. Our goal was to determine whether the same MHC cross-reactive T-cell clones were expressed in each appropriate strain, or whether each T-cell repertoire was unique. The results indicate that identical V alpha-J alpha and V beta-J beta combinations were expressed by the major pigeon cytochrome c-specific response phenotype in B10.A and B10.A(5R) mice. Previous functional data supports this overlap in expressed T-cell clones. B10.A and B10.S(9R) mice exhibit similar response phenotypes to pigeon cytochrome c but express distinctly different TcR genes. The results of these studies support the existence of at least two different mechanisms in determining MHC-linked immune response polymorphisms.

Do endocrines play an etiological role in diabetic and nondiabetic sexual dysfunctions?

Sexually dysfunctional diabetic and nondiabetic males were compared with a group of normal controls using different endocrinological, psychophysiological, and psychological parameters. One hundred male subjects participated in this study: 47 diabetics with sexual dysfunction (DD), 31 nondiabetics with sexual dysfunction (NDD), and 22 normal controls (C). They were evaluated by an internist (physical examination and medical history), a psychologist (psychological and sexual functioning tests), a psychiatrist (psychiatric history and mental status examination), a urologist (genitourinary physical examination), and an endocrine biochemist (evaluation of endocrine factors). Additionally, subjects were evaluated for nocturnal penile tumescence (NPT) during three nights in the sleep laboratory to obtain a differential diagnosis of impotence, that is, psychogenic vs. organic. Both sexually dysfunctional groups showed significant differences on several measures in the psychological and psychophysiological evaluations. There were also significant differences between these two groups and the control group. Plasma levels of total testosterone and serum levels of prolactin, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) showed no significant differences among the three groups, but there were some significant correlations between the endocrine and psychological measures. No significant correlations were found between the endocrine and psychophysiological measures.

Psychiatry and primary care: can a working relationship develop?

This article explores the relationship between psychiatrists and primary care physicians. Expectations and results of attempts to train nonpsychiatric physicians in the care of the mentally ill are reviewed. The failure of this effort, along with the stigma against psychiatry has led to poor treatment of disturbed patients by primary care physicians. Using other mental health professionals as both educators and clinicians in primary care training programs over the past 20 years has resulted in a different referral pattern system for the mentally ill than for any other group of patients. Although the gap between psychiatry and the rest of medicine has widened, there are models of interaction and cooperation that are explored. The development of consultation-liaison programs has been a most important effort. The need for all of medicine to recognize the relationship between mind and body is stressed.