Mechanisms of suppression of cytotoxic T-cell responses in murine lymphocytic choriomeningitis virus infection.

The cytotoxic T-cell response to lymphocytic choriomeningitis (LCM) virus infection was suppressed either in vitro or in vivo by addition of a high level of syngeneic virus-infected cells or syngeneic cells from congenital LCM virus carriers to the environment of the responding cells. This effect was not duplicated by formaldehyde-fixed carrier cells, nor could it be accounted for by 'cold' target competition by carrier cells at the level of the cytotoxicity assay. Conversely, suppression was produced in vivo by water-lysed, ultrasonically treated carrier cell suspensions, or by a large dose of LCM virus equivalent to that contained in the carrier cells. Thus a high level of infectious virus was a common factor in all observed examples of suppression. Based upon this, the following hypothesis, a form of 'forbidden clone deletion,' was proposed to account for virus-specific cytotoxic T-cell tolerance in LCM virus congenital carriers, or in high dose suppression. A high level of virus in lymphoid tissues, while not cytopathic per se, may result in infection of all or most T cells; this then may lead to deletion either via 'suicide' of individual, infected, cytotoxic T cells with receptors specific for virus-induced antigenic patterns on their own surface membranes, or by mutual lysis of two adjacent T cells.

H-2 compatibility requirement for virus-specific T-cell-mediated cytolysis. Evaluation of the role of H-2I region and non-H-2 genes in regulating immune response.

Lymphocytic choriomeningitis virus (LCMV) and ectromelia virus-specific T-cell-mediated cytotoxicity was assayed in various strain combinations using as targets peritoneal macrophages which have been shown to express Ia antigens. Virus-specific cytotoxicity was found only in H-2K- or D-region compatible combinations. I-region compatibility was not necessary nor alone sufficient for lysis. Six different I-region specificities had no obvious effect on the capacity to generate in vivo specific cytotoxicity (expressed in vitro) associated with Dd. Low LCMV-specific cytotoxic activity generated in DBA/2 mice was caused by the non-H-2 genetic background. This trait was inversely related to the infectious virus dose and recessive. Non-H-2 genes, possibly involved in controlling initial spread and multiplication of virus, seem to be, at least in the examples tested, more important in determining virus-specific cytotoxic T-cell activity in spleens than are Ir genes coded in H-2.

H-2 restriction of cell-mediated immunity to an intracellular bacterium: effector T cells are specific for Listeria antigen in association with H-21 region-coded self-markers.

The protective activity of anti-Listeria-immune T cells assayed in an adoptive transfer system in H-2 restricted. As shown in the present studies, the demonstration of the restriction is directly dependent on the dose and the relative protective activity of spleen cells. In addition, some H-2-unrestricted protection is conferred predominantly by other than immunoglobulin-negative spleen cells. Thus, the activity of Listeria-immune T cells appears to be 'absolutely' restricted and is in this respect comparable to in vivo T-cell-mediated anti-viral protection. The predominant genetic region of H-2 coding for the structures which are mainly involved in this restriction in T-cell immunity to this prototype intracellular bacterium is the I region. The specificity of Listeria-immune T cells is determined by the H-2 haplotype of the donor. Thus, F1 hybrids seem to possess at least two separable sets of T cells, each specific for one parental haplotype. As is true in the virus model, the results cannot distinguish between an altered-self or a dual recognition model of T-cell recognition to explain H-2 restriction. They are, however, compatible with the idea and I-coded cell surface structures may serve as receptors for cell-specific differentiation signals, which trigger direct or lymphokin-mediated activation of macrophages to manifest increased bactericidal capacity. The interesting parallels in self-marker recognition of T cells in the virus and intracellular bacterium systems, respectively, appear to be reasonably explained by the different types of signals transmitted by T cells to various target cells via the distinctly different self-markers employed (i.e., K or D vs I).

In vitro primary induction of cytotoxic T cells against virus-infected syngeneic cells.

An in vitro method is described for primary induction of murine cytotoxic T cells against syngeneic cells infected with ectromelia or lymphocytic choriomeningitis (LCM) virus. Cytotoxicity was assayed by 51Cr release from macrophage or L929 target cells. Cytotoxic activity was sensitive to anti-theta and complement and was expressed only against target cells infected with the same virus and sharing H-2K or H-2D genes with the infected stimulator cells. The crucial factors in generating responses were mouse strain, responder: stimulator ratio, nature of infected stimulator cells, and presence of sufficient macrophages. C57BL/6 cells were less demanding than CBA/H and BALB/c cells. Under optimal conditions defined here, the in vitro response had similar kinetics and potency to the primary response in the spleen in vivo.

Protective role of health values in adolescents' future intentions to use condoms.

PURPOSE: To examine the protective role of health values in adolescents' intentions to use condoms. METHODS: Two hundred thirty-six sexually active adolescents who were attending a municipal sexually transmitted diseases clinic were interviewed, using standardized and constructed instruments, regarding their previous condom use, health values, condom attitudes, social norms regarding condoms, self-efficacy regarding condoms, and intentions to use condoms in the future. Correlations and hierarchical multiple regression analyses were conducted to examine the direct and indirect effects of health values on intentions to use condoms. RESULTS: Health values were significantly correlated with intentions to use condoms with main and casual sexual partners, and accounted for a significant amount of variance in intentions to use condoms with casual sexual partners, after controlling for demographic variables, past condom use, and constructs from the Theory of Planned Behavior. Health values were also found to moderate the relationship between condom attitudes and intentions to use condoms with casual partners. CONCLUSIONS: Efforts to include health values as a protective factor in health behavior theory and risk-reduction interventions are warranted.

Secondary cytotoxic cell response to lymphocytic choriomeningitis virus. I. Kinetics of induction in vitro and yields of effector cells.

Secondary (memory) cell-mediated cytotoxic responses in lymphoid cells from CBA/H mice pre-primed with lymphocytic choriomeningitis virus (LCM) 5-7 weeks previously were induced by culturing these cells in vitro with syngeneic, infected peritoneal cells at 37 degrees for periods of up to 5 days. Cytotoxic effectors were assayed against LCM infected, H-2 compatible target cells in a 51Cr release assay. Response was greater with a higher ratio (1:10) of infected peritoneal cells:pre-primed cells than with lower ratios (e.g. 1:250). Separating responders from infected cells by a 450 mmum nucleopore membrane (coarse enough to allow passage of virus particles) still permitted induction of a secondary response whilst interposition of a 50 mmum nucleopore membrane (which apparently prevented transit of virus particles) virtually abolished the secondary response. Removal of phagocytic cells from responders prior to setting up memory cultures greatly reduced responders' capacity to be induced. Fixed, infected stimulators still induced strong secondary responses. Secondary response was maximal with spleen cells, peripheral blood lymphocytes, or pooled iliac and lumbar lymph node cells. Thymocytes responded less well, whilst mesenteric lymphoid cells and peritoneal cells gave minimal responses. Effector cells from memory cultures killed targets with single-hit kinetics and a rectilinear log effectors: log targets lysed relation held. Memory spleen cells developed increasing cytolytic activity from 2 to 5 days in culture. Memory-generated effectors were markedly potent by day 5, e.g. giving 70 per cent specific release at a killer:target ratio of 0-8:1. Peak DNA synthesis occurred on day 4. We conclude that memory effectors as a population differ in kinetics and potency from effectors obtained by primary viral challenge in the mouse.

Cytotoxic T cell activity is strain-specific in outbred mice infected with lymphocytic choriomeningitis virus.

The cytotoxic T cell response in outbred mice infected with lymphocytic choriomeningitis virus (LCMV) is strain specific. The same is true for adoptive transfer of fatal LCM disease. The response of individuals within an outbred strain is completely cross-reactive, as shown by using immune lymphocytes and virus-infected macrophage targets from individual mice. Reciprocal exclusion of cytotoxic T cell activity between inbred and outbred mouse strains is the rule, the exception being one strain (H) known to have some C57BL ancestry. Immune T cells from one of 7 H mice specifically lysed LCMV-infected C57BL macrophages. Experiments with inbred mice have shown that only one allele need be shared at either the H-2K or H-2D locus for cytotoxic T cell activity to be manifest. Adoptive transfer protocols may thus be considered in outbred situations, providing that T cells are effective before allograft rejection occurs. Also, the LCMV cytotoxic T cell assay may be useful for determining the degree of H-2 variability in wild mouse populations, as novel H-2 types can be detected and mice need not be congenic.

Secondary cytotoxic cell response to lymphocytic choriomeningitis virus II. Nature and specificity of effector cells.

The method described in the previous paper was used to induce secondary responses in spleen cells from CBA/H mice, pre-primed with lymphocytic choriomeningitis (LCM) virus by culturing them with LCM-infected peritoneal cells. The cytolytic effector cells thus generated have been characterized. Effector cells were sensitive to treatment with anti-theta ascitic fluid and complement. Separation procedures based on rosetting of certain categories of lymphocytes with sheep red cells through an Isopaque-Ficoll gradient indicated that effector cells lacked surface immunoglobulin and generally did not bear Fc receptors. Cytolytic activity was restricted by the H-2 gene complex. Killing had single-hit characteristics. All these results suggested that the cells from memory cultures mediating cytolysis were T cells. There was evidence for two T cell subsets, a major subpopulation directed against antigens on infected targets and a minor one directed against antigens on uninfected, H-2-compatible targets. Specificity was present at the infected cell:memory responder and killer:target levels between LCM virus (an arenavirus) and ectromelia virus (a poxvirus).

Concurrent sex partners and risk for sexually transmitted diseases among adolescents.

BACKGROUND/OBJECTIVES: A large percentage of sexually active adolescents have multiple sex partners and are at high risk of acquiring sexually transmitted diseases (STDs). Little is known about adolescents' patterns of sexual partnerships (e.g., concurrent versus serial) and how these patterns influence STD risk. GOAL OF THE STUDY: To determine the frequency with which adolescents have concurrent partners during a main relationship and the association between having concurrent partners and STD risk. STUDY DESIGN: Adolescents seeking care at a public STD clinic were recruited from March, 1996, to May, 1998. Demographic and behavioral data were obtained during an interviewer-administered questionnaire. Sexually transmitted disease testing and physical exams were performed by clinicians. RESULTS: Of those adolescents who reported having at least one main partner during the previous 6 months (n = 245), 110 (44.9%) had multiple partners, and 76 (31%) had at least one concurrent partner during a main relationship. Greater number of concurrent partners was associated with STD diagnosis/exposure after controlling for number of sex partners (OR = 1.6; 95% CI, 1.1-2.4). CONCLUSIONS: A significant percentage of adolescents have concurrent partners during a main relationship, and having concurrent partners increases STD risk.

Changes in the surface of virus-infected cells recognized by cytotoxic T cells. II. A requirement for glycoprotein synthesis in virus-infected target cells.

Infection of cells with either ectromelia or lymphocytic choriomeningitis (LCM) virus in the presence of 2-deoxy-D-glucose (2-DOG) inhibited by up to 70% the extent to which the infected cells become susceptible to virus-specific cell-mediated lysis. The concentration of 2-DOG used had little effect on the extent of total protein synthesis (incorporation of [35S] methionine) but inhibited (up to 25%) glycoprotein synthesis, as measured by incorporation of [3H] fucose. This suggested that glycoprotein synthesis was a necessary event for infected cells to become susceptible to T-cell mediated lysis. The profiles (polyacrylamide gel electrophoresis) of newly synthesized, cellular glycoproteins from unifected and ectromelia-infected cells in the presence and absence of 2-DOG were compared and found to be very complex, with only minor changes. However, when convalescent serum from infected mice was used to isolate newly synthesized components from the cell surface shortly after infection, it showed four main species ranging in size from 25,000 to 70,000 daltons. 2-DOG inhibited production of these by 70%, thus corresponding to the biological data. The nature of the new glycoproteins seen in infected cells and whether they are in fact the structures recognized by effector T cells remain to be determined.

Inflammatory process in murine lymphocytic choriomeningitis is maximal in H-2K or H-2D compatible interactions.

Capacity to transfer adoptively fatal lymphocytic choriomeningitis (LCM) to immunosuppressed, virus-infected recipients is a property of H-2 compatible, non-Ig-bearing virus-immune lymphocytes. Severe meningitis is recognized when donor and recipient share at least one allele at either H-2K or H-2D. Presence of unshared H-2 genes is not obviously inhibitory, and identity at the immune response (Ir) region of the H-2 gene complex is neither sufficient nor necessary. The same constraint applies to cytotoxic T cell activity in vitro; lymphocytes and virus-infected targets must be compatible for a minimum of one allele mapping at H-2K or H-2D. The present findings thus support the concept that populations of T cells, which are cytotoxic in vitro, also mediate inflammatory process in vivo and are a major, if not the only, effector population in murine LCM.