Characterization of the murine antigenic determinant, designated L3T4a, recognized by monoclonal antibody GK1.5: expression of L3T4a by functional T cell clones appears to correlate primarily with class II MHC antigen-reactivity

The contribution of L3T4+ T cells to lymphoproliferation and autoantibody production in MRL-lpr/lpr mice

The current study examines the role of the L3T4 T cell subset in the development of lupus-like autoimmunity and lymphoproliferation in lpr-bearing mice. Chronic treatment of MRL-lpr/lpr mice with anti-L3T4 antibody beginning at 4 wk old was found to markedly decrease the production of IgG anti-DNA and antihistone antibodies, while having no effect on IgM autoantibodies. A dramatic reduction in splenomegaly and lymphadenopathy was also observed coincident with a decrease in the percentage and total number of Thy-1+, B220+ cells. Together, the data suggest an important role for L3T4+ T cells in the pathogenesis of disease in lpr mice and provide further evidence that a requirement for the L3T4 subset may be a common feature of murine autoimmunity.

Predominant expression of a T cell receptor V beta gene subfamily in autoimmune encephalomyelitis

TCR beta chain gene expression of individual T cell clones that share the same MHC class II restriction and similar fine specificity for the encephalitogenic NH2 terminus of the autoantigen myelin basic protein (MBP) has been examined. TCR V beta expression was examined by FACS analysis with mAbs specific for the V beta 8 subfamily of TCR beta chain genes. 14 of 18 (78%) NH2-terminal MBP-specific clones examined express a member of the TCR V beta 8 subfamily. Southern analysis was used to identify which member(s) of the TCR V beta 8 subfamily is expressed by these clones. Each of four clones examined uses V beta 8.2, though two different V beta 8.2-J beta 2 combinations were identified. Our findings indicate that there is restricted TCR V beta usage in the autoimmune T cell response to the dominant encephalitogenic NH2-terminal epitope of the MBP. The use of an mAb to the antigen-specific TCR in the prevention of T cell-mediated autoimmune disease has been investigated. Our results demonstrate that in vivo administration of a TCR V beta 8-specific mAb prevents induction of autoimmune encephalomyelitis.

Role of gamma interferon in induction of natural killer activity by Legionella pneumophila in vitro and in an experimental murine infection model

Legionella pneumophila has been shown to induce gamma interferon (IFN-gamma) both in vitro and in vivo during experimental infections of mice. With complement-mediated serologic depletion of murine splenocytes, the cellular sources of IFN-gamma following in vitro stimulation with L. pneumophila antigens were Thy-1.2+, Lyt-2-, L3T4-, and asialo-GM1+, which is consistent with the natural killer (NK) cell phenotype. Additionally, Percoll density discontinuous centrifugation demonstrated that maximal production of IFN coincided with high NK activity in fractions which were enriched for large granular lymphocytes. Furthermore, 18- to 24-h incubation of splenocytes with L. pneumophila whole-cell vaccine resulted in augmented NK cytotoxic activity against YAC-1 tumor target cells in a 51Cr release assay. The addition of macrophages to purified large granular lymphocyte populations augmented both IFN-gamma production and NK activity, suggesting that antigen is required for optimal responses. In an experimental infection model using an intratracheal inoculation route, NK activity was enhanced in the spleen, peripheral blood, and lung cells of infected mice, with maximal stimulation in the lung leukocytes at the site of infection. The results of the present study indicate that NK cells respond in vivo and in vitro to stimulation by L. pneumophila by producing IFN-gamma and by increased cytolytic activity.

Differentiation of thymocytes in fetal organ culture: lack of evidence for the functional role of the interleukin 2 receptor expressed by prothymocytes

Thymic rudiments of 14-day-old mouse embryos were put into organ culture in the presence of interleukin 2 (IL2) and PC.61, a monoclonal antibody that binds to the IL2 receptor (IL2R). After 5 and 7 days of culture, we found no influence of PC.61 on the growth of the thymus and the composition of the thymocyte subpopulations as studied with a panel of monoclonal antibodies. High-dose IL2 treatment of the organ culture resulted in a reduction of the number of thymocytes and a decrease in the single CD4+ and CD4+CD8+ thymocytes, whereas the number of CD8+Ly-1+ thymocytes and the number of CD4-CD8-Ly-1- IL2R+ thymocytes increased. The effect of high-dose IL2 treatment was ascribed to the induction of a nonspecific LAK activity. Our findings argue against a functional role of IL2R on prothymocytes during early T cell development.

In vivo and in vitro studies of the prevention of proteolipid apoprotein-induced murine experimental allergic encephalomyelitis by monoclonal antibody against L3T4

The suppressive effect of anti-L3T4 monoclonal antibody (mAb) on murine experimental allergic encephalomyelitis (EAE) induced by sensitization with proteolipid apoprotein (PLP) was examined in vivo and in vitro. This mAb inhibited the antigen-specific proliferation of the encephalitogenic T cell lines but did not block the mitogen-mediated response. Serial injections of the mAb during the pre-effector phase of EAE markedly suppressed the development and relapse of the disease but this treatment initiated after appearance of clinical signs was not effective. In treated animals, L3T4+ T cells in the spleen were profoundly decreased and the antigen-specific proliferative response of spleen cells was completely suppressed. Moreover, adoptive transfer of spleen cells from the treated mice induced resistance against EAE induction in the recipients. However, no obvious evidence for antigen-specific suppressor cells was found in vitro in the L3T4- populations of spleen cells from treated mice.

Epitopes associated with major histocompatibility complex (MHC) restriction site of T cells. IV. I-J epitopes on MHC-restricted cloned T cells

We studied the expression of an I-Jk epitope on class II-restricted cloned L3T4+ T cells established from H-2k, H-2b, F1 and semiallogeneic radiation bone marrow chimeras by the inhibition of antigen-induced T cell proliferation and in vitro secondary antibody response, and by the direct immunofluorescence with a monoclonal anti-I-Jk. Both I-Ak- and I-Ek-restricted T cells were shown to carry the identical I-Jk epitope regardless of their genotypic origins, antigen specificity, and helper or suppressor function. None of the I-Ab-restricted clones derived from similar animals showed the I-Jk epitope. This isomorphism, regardless of the restriction specificity for I-Ak or I-Ek, contradicts the idea that I-J is an idiotypic determinant on class II-restricted T cell antigen receptor (TcR). In fact, the I-Jk epitope was not comodulated with TcR/T3 complex when incubated with an anti-T3 antibody, indicating that I-J is a new isomorphic receptor for self different from TcR alpha/beta heterodimers.

A nonstructural viral protein expressed by a recombinant vaccinia virus protects against lethal cytomegalovirus infection

The nonstructural immediate-early protein pp89 of murine cytomegalovirus (MCMV) is the first viral protein synthesized after infection and has a regulatory function in viral gene expression. Despite its localization in the nucleus of infected cells, pp89 is also the dominant antigen recognized by MCMV-specific cytolytic T lymphocytes. The recombinant vaccinia virus MCMV-ieI-VAC, which expresses pp89, was used to study the capacity of this protein to induce protective immunity in BALB/c mice. Vaccination with MCMV-ieI-VAC induced a long-lasting immunity that protected mice against challenge with a lethal dose of MCMV but did not prevent infection and morbidity. In vivo depletion of CD8+ T lymphocytes before challenge completely abrogated the protective immunity. CD8+ T lymphocytes derived from MCMV-ieI-VAC-primed donors and adoptively transferred into sublethally irradiated and MCMV-infected recipients were found to limit viral replication in host tissues, whereas CD4+ T lymphocytes and pp89-specific antiserum had no protective effect. The data demonstrate for the first time that a single nonstructural viral protein can confer protection against a lethal cytolytic infection and that this immunity is entirely mediated by the CD8+ subpopulation of T lymphocytes.

Immunotherapy of the nonobese diabetic mouse: treatment with an antibody to T-helper lymphocytes

Spontaneous diabetes mellitus was blocked in nonobese diabetic mice by treatment with a monoclonal antibody against the L3T4 determinant present on the surface of T-helper lymphocytes. Sustained treatment with the monoclonal antibody led to cessation of the lymphocytic infiltration associated with the destruction of the insulin-producing beta cells. Moreover, the mice remained normoglycemic after the antibody therapy was stopped. These studies indicate that immunotherapy with monoclonal antibodies to the lymphocyte subset may not only halt the progression of diabetes, but may lead to long-term reversal of the disease after therapy has ended.

Control of helper-T-cell proliferation by recognition of Ia and Mac-1 antigens on phagocytic cells of the thymic reticulum

Phagocytic cells of the thymic reticulum (P-TR) have been previously described as being Ia-positive, Mac-1-positive accessory cells which pursue a close relationship with thymocytes. They form rosettes with thymocytes, and these rosettes are inhibited by antibody directed against the complement receptor type 3 CR3 (anti-Mac-1). P-TR induce the proliferation of syngeneic thymocytes. In the present paper, we show that thymocytes enriched in mature medullary type are induced to proliferate in coculture with syngeneic P-TR, while the cortical type does not. After 5 days of culture, 85% of the thymocytes are of helper L3T4+Lyt-2- phenotype. As previously shown by others for syngeneic reactions, antibodies directed against related class II antigens (anti-I-A and anti-I-E) block this helper-T-cell syngeneic proliferation. A new finding is the blockage of helper-T-cell proliferation by anti-Mac-1 as well as with anti-LFA-1 antibodies, showing that accessory molecules may be as important as specific recognition of class II antigen molecules in the control of thymocyte proliferation and hence in thymocyte selection. Mac-1, like LFA-1, belongs to a novel family of differentiation antigens involved in cell interactions. The blockage of cell recognition and interaction between P-TR and thymocytes by either anti-Ia or anti-Mac-1 during the early induction phase of the syngeneic response leads to its inhibition. We demonstrate that P-TR/thymocyte interaction stimulates the enhanced expression of IL-2 receptors on thymocytes, a step which is necessary for helper-T-cell proliferation. The mechanism of syngeneic proliferation inhibition by anti-Ia, anti-Mac-1, and LFA-1 antibodies may be the prevention of IL-2 receptor expression on thymocytes, and/or the inhibition of IL-2 secretion. Although this is an in vitro model, which may not totally reflect in situ situation, our results indicate that thymic accessory cells may participate in a positive selection process which leads to helper-T-cell proliferation.

Acquisition of an additional antigen specificity after mouse CD4 gene transfer into a T helper hybridoma

We have transfected the mouse CD4 gene into a beef insulin (BI)-specific murine T helper hybridoma that lacks CD4 surface expression. The CD4-expressing transfectants have acquired an additional reactivity for pork insulin (PI), which was not detectable in the original recipient cell. The transfectants' response to PI can be completely abrogated by anti-CD4 antibodies. The transfected clone showed a 50-fold increased sensitivity towards BI in comparison to the same CD4- hybridoma. These experiments suggest that CD4 may be important in determining the antigen fine specificity and, therefore, may also play a role in altering the T cell repertoire.

Effect of T cell modulation on the translocation of bacteria from the gut and mesenteric lymph node

Although the ability of the gut-associated lymphoid tissue (GALT) to respond to orally ingested foreign antigens has been studied extensively, its function in preventing or limiting escape of resident gut bacteria has not been assessed. The following studies were performed to examine what role cell-mediated immunity (CMI) plays in this process. The ability of suppression of CMI to induce escape of gut bacteria (translocation) to the mesenteric lymph node (MLN) in immunocompetent mice whose gut flora was unaltered was examined. Administration of cyclosporine or anti-L3T4 antibody failed to induce translocation of indigenous gut bacteria after 7 or 14 days of treatment. Antithymocyte globulin (ATG) also failed to induce translocation after 7 days of treatment, despite depletion of all Thy 1, Lyt 1, L3T4, and Lyt 2 positive cells from the spleen, MLN, and intestine as demonstrated by immunofluorescent microscopy. Finally, cultures of the MLN, spleen, liver, and peritoneum of T cell-deficient BALB/c nude mice and their heterozygous T cell-replete littermates were also sterile, demonstrating that congenital suppression of T CMI also does not lead to translocation of indigenous gut bacteria. The role of CMI in limiting systemic spread of bacteria that were already translocating to the MLN was also examined. Translocation of Escherichia coli C25 to the MLN was induced by gastrointestinal (GI) monoassociation, which leads to translocation of E. coli C25 to the MLN in 80-100% of mice. Treatment with ATG during monoassociation failed to induce spread of E. coli C25 to the spleen, liver, or peritoneum, despite the same degree of T cell depletion achieved with ATG in the previous experiment. Monoassociation of conventional T cell-deficient BALB/c nude and heterozygous mice and germ-free T cell-deficient BALB/c nude and heterozygous mice also did not lead to spread of E. coli C25 beyond the MLN. However, in ATG-treated, conventional nude, and germ-free nude mice, the average number of translocating E. coli C25 per MLN was consistently higher. In separate experiments the ability of stimulation of T cell function to inhibit translocation of E. coli C25 was examined. Recombinant interleukin-2, 25,000 units, was administered intraperitoneally every 8 hours during exposure to E. coli C25. This reduced the incidence of translocation of E. coli C25 from 85% to 51% (p = 0.02). Suppression of CMI, either systemically or within the GALT, has a minimal influence on the mechanisms by which the normal gut flora are translocated to the MLN.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of Lyt-2+ T cells in the regulation of autoimmunity in murine lupus

Systemic lupus erythematosus (SLE) in humans and in mice is characterized by reduced suppressor T-cell activity. This observation suggests that selective loss or impaired function of suppressor T cells may contribute to the development of autoimmunity. To clarify the role of suppressor T cells in the pathogenesis of SLE, we used a rat MAb to selectively deplete Lyt-2+ ('suppressor/cytotoxic') T cells from lupus-prone NZB/NZW F1 (B/W) mice. Treatment consisted of weekly intraperitoneal injections of anti-Lyt-2 (2 mg/mouse) beginning at age 4 months, prior to the onset of overt clinical illness. Control mice received weekly injections of either non-immune rat IgG or saline. Despite sustained depletion of Lyt-2+ T cells, mice treated with anti-Lyt-2 were indistinguishable from control mice with respect to production of anti-DNA antibodies, development of renal disease, and mortality. These findings imply that Lyt-2+ T cells do not regulate autoimmunity in B/W mice. However, they do not exclude the possibility that Lyt-2+ T cells suppress autoimmunity in normal mice but are simply non-functional in B/W mice. Therefore, we also examined the consequences of depleting Lyt-2+ T cells from non-autoimmune C57BL/6 x NZW (B6/NZW) mice. Depletion of Lyt-2+ T cells from B6/NZW from age 4 to 10 months produced neither serologic nor clinical evidence of murine lupus. These observations suggest that suppressor T cell defects are not sufficient to cause murine lupus.

TAP transcription and phosphatidylinositol linkage mutants are defective in activation through the T cell receptor

TAP is a phosphatidylinositol-anchored membrane protein that is involved in murine T lymphocyte activation. To determine the relationship between TAP and T cell receptor/CD3-mediated activation, we derived TAP expression mutants of a T-T hybridoma. Two phenotypically distinct classes of mutants were obtained. The first has a selective defect in the transcription of TAP, while the second has a defect in the biosynthesis of phosphatidylinositol-protein linkages. Both mutations affect antigen-stimulated, T cell receptor-mediated activation of the T-T hybrid. These variants have intact immune effector gene programs, as they are responsive to pharmacologic agents that mimic receptor signals. These findings support a role for phosphatidylinositol-linked cell-surface glycoproteins in physiologic T cell activation. Consistent with this interpretation, we observed similar defects in T cell responsiveness after enzymatic removal of phosphatidylinositol-linked proteins from normal T lymphocytes.

Stimulation and proliferation of CD4+ peripheral blood T lymphocytes induced by an anti-CD4 monoclonal antibody

There is experimental evidence that the CD4 molecule participates in the antigen-driven activation of T cells expressing this surface glycoprotein. Whether CD4, a member of the immunoglobulin supergene family, acts as a ligand-binding molecule and/or is directly involved in the activation pathway has yet to be established. In this study, we show that human CD4+ lymphocytes can be activated by exposure to the anti-CD4 monoclonal antibody (mAb) B66. Normal peripheral blood CD4+ cells were induced to proliferate and to synthesize interleukin 2 (IL 2) by the antibody. The specificity of the antibody stimulatory activity was tested by using IL 2-producing clones bearing either CD4 or CD8 on their surface. IL 2 production was induced by mAb B66 in CD4+, but not CD8+, clones, whereas both types of clones responded to stimulation by the anti-CD3 mAb Leu-4. Despite its unique stimulatory activity, mAb B66 shared with other anti-CD4 antibodies the ability to inhibit the specific cytolytic activity of CD4+ effector cells. These results clearly indicate that cross-linking of surface CD4 molecules with appropriate antibodies can fully activate CD4+ lymphocytes. Whether the natural ligand for CD4 can trigger this activation pathway remains to be defined.

A noncognate interaction with anti-receptor antibody-activated helper T cells induces small resting murine B cells to proliferate and to secrete antibody

Culture of small resting allogeneic B cells (of an irrelevant haplotype) with two clones of T helper (Th) cells that were activated by the F23.1 anti-T cell receptor antibody led to the activation of B cells to proliferate and to secrete antibody. Th cell supernatants by themselves had no effect on resting B cells (even in the presence of intact F23.1 antibody), but could induce antibody secretion by anti-Ig-preactivated B cells. Both F23.1+ clones (E9.D4 and 4.35F2) and one F23.1- clone (D2.2) could synergize with supernatants from activated E9.D4 T cells to induce B cell activation. F(ab')2 fragments of F23.1 induced E9.D4 to activate B cells as efficiently as intact F23.1 and B cell populations that had been incubated with F23.1 were not activated when cultured with E9.D4, although T cells recognized cell-presented F23.1 and were weakly activated. Reduction of the density of F23.1 adsorbed to plastic resulted in weak T cell activation, and these T cells did not induce B cell responses. Haptenated B cell populations, although recognized by E9.D4, were not activated. Separation of T and B cells by a 0.4-micron membrane prevented T-dependent B cell activation, although Th cell-derived B cell-activating lymphokines would be assayed across these membranes. These results suggest a polyclonal noncognate B cell activation that depends on physical contact between B cells and activated T cells. The requirement for a cognate interaction of Th with B cells for the production and delivery of B help can therefore be overcome by activating Th cells with high densities of T cell receptor ligands.

Qualitative and quantitative heterogeneity in Pgp-1 expression among murine thymocytes

A proportion of Pgp-1+ cells in the thymus have been shown to have progenitor activity. In adult AKR/Cum mice the total Pgp-1+ population in the thymus differs from that of the bulk of thymocytes and is antigenically heterogeneous when examined by flow cytometry. Pgp-1+ thymocytes are enriched for several minor cell populations compared to total thymocytes: B2A2-, interleukin-2-receptor+ (IL-2R+), and Lyt-2-, L3T4-. However, these subsets are still a minor proportion of the Pgp-1+ cells, the majority being Lyt-2+ and/or L3T4+ and B2A2+. Pgp-1+ thymocytes also differ from the bulk of thymocytes in having lower amounts of Thy-1 and in showing a higher proportion of single positive (Lyt-2+, L3T4- or Lyt-2-, L3T4+) cells. Populations of adult thymocytes that are enriched in progenitor cells can be isolated by cytotoxic depletion using either anti-Thy-1 antibody (Thy-1 depletion) or anti-Lyt-2 and anti-L3T4 antibody (Lyt-2, L3T4 depletion). Pgp-1+ cells in progenitor cell-enriched populations are also phenotypically heterogeneous. Pgp-1+ cells in both populations may be IL-2R+ or IL-2R- and B2A2+ or B2A2-. The population of Pgp-1+ cells in progenitor cell-enriched populations in the adult differs from that of the fetus at 14 days of gestation in that in the 14-day fetus, most Pgp-1+ cells are IL-2R+. By Day 15 of gestation, distinct populations of Pgp-1+, IL-2R-; Pgp-1+, IL-2R+; and Pgp-1-, IL-2R+ cells are observed. In the 15-day fetus, as in the adult, many Pgp-1+ thymocytes express low to moderate levels of Thy-1. The total percentage of Pgp-1+ cells in the thymus varies among different mouse strains, ranging from 4 to 35% in the thymus of young adult mice. Pgp 1.1 strains contain more detectably Pgp-1+ thymocytes than Pgp 1.2 strains; however, there is variability in the proportion of Pgp-1+ cells, even among Pgp 1.2 strains. In contrast to AKR/Cum mice, the Pgp-1+ thymocyte population in BALB/c mice, which contain a high proportion of Pgp-1+ thymocytes, closely resembles the total thymocyte population.

Serological characterization of macrophage hybridomas: identification of an interferon-gamma-inducible surface marker

Macrophage hybridoma clones prepared by fusion of splenic adherent cells with P388D1 tumor cells have previously been shown to be heterogeneous with respect to function at the clonal level. In this study the macrophage clones were phenotypically characterized by indirect RIA using a battery of rat MAbs to murine myeloid and lymphoid cell surface markers. All macrophage clones expressed the common leukocyte antigen T200 and the Mac-1 alpha and beta chains. Markers which were differentially expressed among the clones included class II antigens and the antigens detected by MAbs MIV 55, MIV 38, and 14G8. The antigens detected by the latter three MAbs were referred to as MBR-1, -2 and -3, respectively. Functional heterogeneity did not correlate with phenotypic heterogeneity among the macrophage clones. Treatment of macrophage clones with IFN-gamma resulted in a significant increase in the expression of class II antigens and induced the expression of MBR antigens on some clones which were constitutively negative for these markers. The clonal distribution and induction patterns of class II antigen as compared to MBR antigen indicated that regulation of expression of these markers was independent. In addition, the clonal distribution and induction pattern of MBR antigens, along with competitive binding studies using radiolabeled MIV 38 and 14G8 MAbs, suggested that the three MBR antigens were similar or closely associated molecules.

The role of T cell subpopulations in cell mediated immunity to facultative intracellular bacteria

This brief review summarizes the experimental data which underly the classic concept of antibacterial cell mediated immunity and will integrate recent developments focusing on results obtained by in vivo studies in the model of rodent listeriosis.

Adoptive immunotherapy of murine cytomegalovirus adrenalitis in the immunocompromised host: CD4-helper-independent antiviral function of CD8-positive memory T lymphocytes derived from latently infected donors

The ability of memory T lymphocytes derived from latently infected mice to control murine cytomegalovirus disease in the immunocompromised host was studied by adoptive transfer experiments. At a stage of pathogenesis when virus had already colonized target tissues, a therapeutic antiviral function could be ascribed to the CD8+ subset. This in vivo function was not restricted to sites in which intravenously infused lymphocytes usually are trapped or home in, such as the lungs or the spleen, respectively, but was also evident in the adrenal glands, a site to which antiviral effector cells have to specifically migrate. Specific infiltration of adrenal gland cortical tissue by donor-derived CD8+ memory T lymphocytes was demonstrated. CD4+ memory T lymphocytes had no antiviral effect by themselves and also were not required for the function of the CD8+ effector cells in this short-term immunotherapy model. These findings should help settle the debate about which subset of T lymphocytes comprises the effector cells that can directly control cytomegalovirus infection in the murine model system.

Responsiveness of T cells to mutant major histocompatibility complex class I antigen. I. Obligatory dependence of proliferative response on the presence of stimulator type accessory cells

Proliferative response of splenic T cells of C57BL/6 mice to mutant major histocompatibility complex (MHC) class I antigen (H-2Kbm1) was examined with regard to the role of accessory cells. T cell proliferation in mixed lymphocyte culture (MLC) was not induced when accessory cells were removed from stimulator spleen cells by passage through Sephadex G-10 or nylon-wool column. Anti-Iab antibodies did not inhibit the proliferative response to class I antigen, whereas the same antibodies completely blocked the response to class II antigen (Iabm12). Accessory cells may not be mere presenters of MHC class I antigen because stimulator cells fixed with 0.05% paraformaldehyde lost the stimulating function. The proliferative response was partially recovered by the addition of recombinant interleukin 1 (IL-1) and/or IL-2 to MLC devoid of stimulator type accessory cells. It is concluded that stimulatory type accessory cells were obligatorily involved in the T cell proliferation, and the production of IL-1 by accessory cells is thought to play a critical role in this process.

The lpr gene causes an intrinsic T cell abnormality that is required for hyperproliferation

The lpr gene induces marked lymphoproliferation characterized by the massive accumulation of T cells of an unusual phenotype and concomitant autoimmune disease. To clarify the mechanism of the lpr effect, bone marrow cells from B6-lpr/lpr (Ly-1.2) and B6-+/+ (Ly-1.1) mice were transferred into lethally irradiated B6-lpr/lpr mice. As has been previously reported, recipients of the B6-lpr/lpr bone marrow showed the typical lpr phenotype with marked lymphadenopathy, splenomegaly and increased levels of autoantibodies; while the recipients of B6-+/+ bone marrow had normal sized lymph nodes and spleen and no autoantibodies. A third group of mice received an equal mixture of bone marrow cells from the B6-lpr/lpr and B6-+/+ donors. These mice showed both lymphadenopathy and autoantibody production comparable to that of recipients of the B6-lpr/lpr marrow alone. Immunofluorocytometric analysis of the lymphoid populations in these mixed bone marrow recipients established that the T cells from the lpr/lpr and +/+ donors were equivalently represented in the peripheral blood and thymus. In striking contrast, the T cells that accumulated in abnormally large numbers in the lymph nodes were almost entirely from the lpr donor. Their surface phenotype was Thy-1+(dull), Ly-1.2+(dull), Lyt-2-, L3T4-, 9F3+, and 3A1+, which is consistent with that found in intact lpr mice. These results indicate that the lpr gene causes an intrinsic defect directly within the T cells that accumulate in large numbers in lpr mice. In addition, the presence of the +/+ T cells cannot prevent the expression of the lpr abnormalities.

Asialo GM1 as an accessory molecule determining the function and reactivity of cytotoxic T lymphocytes

The expression and function of asialo-GM1 (AsGM1) in alloreactive cytotoxic T lymphocytes (CTL) was studied. We have shown previously that the cytotoxic reactions mediated by AsGM1+-cloned CTL were blocked by anti-AsGM1 or by purified AsGM1. To further determine the role of AsGM1 in CTL-mediated cytotoxicity, we examined the correlation between this blocking effect and the expression of AsGM1 on effector and target cells. Now we found that the blocking by anti-AsGM1 was largely dependent on the expression of AsGM1 on the effector cells in a dose-dependent fashion. The expression of AsGM1 on target cells had only little effect on the blocking of cytotoxic reactions by anti-AsGM1 or AsGM1. A threefold difference was seen in the blocking of AsGM1+ and AsGM1- targets. The observation was in sharp contrast to the effectors as no blocking was ever seen with AsGM1- CTL. Similar to CTL effectors, we found that the expression of AsGM1 and L3T4 were mutually excluded on mitogen-activated T cells, despite the fact that they could coexpress in resting T cells. The expression of AsGM1 on CTL effectors was associated with the antigen-nonspecific natural killer (NK)-like or lymphokine-activated killer (LAK)-like activity exerted by the alloreactive CTL. All AsGM1+ CTL possessed LAK activity against antigen-unrelated tumor targets, and the AsGM1- CTL only displayed antigen-specific alloreactivity. The LAK activity was associated with the expression of AsGM1 on effectors, and was not related to the AsGM1 expression on target cells. These findings indicate that the AsGM1 expressed on alloreactive CTL may function as an accessory molecule for T-cell receptors in the antigen-specific alloreactive cytotoxicity mediated by AsGM1+ CTL. The expression of AsGM1 may also be related to the activation of an NK-like apparatus in these CTL. Therefore, AsGM1 not only may be involved in cytotoxic reactions mediated by AsGM1+ CTL, it may also modulate the specificity of the CTL cytotoxicity.

Cell-mediated immunity to chemically xenogenized tumors. II. Evidence for accessory function and self-antigen presentation by a highly immunogenic tumor variant

To determine whether antigen-presenting ability might be involved in the superior immunogenicity of chemically xenogenized tumors over that of parental cells, we tested a murine lymphoma line xenogenized by a triazene derivative for expression of Ia antigens, ability to present soluble antigen in vitro, and production of factor(s) active in a mouse thymocyte assay. Results showed that Ia antigens, absent on nonimmunogenic parental L5178Y cells, were expressed on a xenogenized, highly immunogenic tumor variant (clone D), as detected by immunofluorescence. While the ability of parental cells to stimulate lymphocyte proliferation in vitro was lost on removal of Ia+ cells from the responder population, considerable augmentation of reactivity was observed upon depletion of Ia+ cells from the population of splenocytes responding to the xenogenized cells. Under these conditions, stimulation was blocked by anti-Ia antibodies, or an anti-L3T4 reagent or antibodies to the novel antigenic determinants induced by xenogenization. In addition, no stimulating activity was observed following exposure of clone D cells to glutaraldehyde or lysosomotropic agents such as chloroquine and ammonia. When the ability of clone D cells to present ovalbumin in vitro was assayed, it was found that the xenogenized cells could present the soluble antigen to specifically primed lymphocytes. Moreover, clone D cells could substitute for splenic adherent cells in the proliferative reaction of splenocytes to concanavalin A. Finally, when the supernate from clone D-cell culture pulsed with phorbol myristic acetate was tested in a mouse thymocyte assay, considerable IL-1-like activity was disclosed.

Immunocytochemical examination of immune cells in periapical granulomata and odontogenic cysts

Monoclonal antibodies (mAbs) were used to determine the presence and distribution of immune cells including lymphocytes, macrophages and Langerhans cells, in normal periodontal ligament, periapical granulomata, periapical cysts and dental developmental cysts. Isolated T-lymphocytes, but not B-lymphocytes, were detected in specimens of non-inflamed periodontal ligament. Increased numbers of T and B lymphocytes were found in all of the lesions examined. Monocytes/macrophages were associated with most periapical granulomata, dental developmental cysts and all periapical cysts. Langerhans cells, intraepithelial lymphocytes, and monocytes/macrophages were not detected in the rests of Malassez but were found in some epithelia within periapical granulomata and in most epithelial linings of odontogenic cysts. Increased numbers of immune cells were seen around proliferative epithelia and adjacent to the epithelial linings of cysts. Epithelium, particularly that of odontogenic cysts, showed positive reactions for HLA-Dr, lysozyme and for alpha-1 antitrypsin. The presence of immune cells in periapical granulomata and odontogenic cysts, suggests that cell-mediated and humoral immunoreactions occur in these lesions and may be associated with the epithelial proliferation within the periapical lesions.

The secondary in vitro murine cytotoxic T cell response to the flavivirus, West Nile

A secondary in vitro murine cytotoxic response to the flavivirus, West Nile (WNV) is described. Cytotoxic activity was obtained from spleen cells of mice primed 7 days previously with 10(6) p.f.u. WNV and boosted in vitro for a further 5 days with WNV-infected stimulator spleen cells. The cells responsible for lysis of WNV-infected target cells were restricted by class 1 H-2 antigens. The K region of the H-2k haplotype and both the K and D regions of the H-2d haplotype were permissive. The cytotoxic cells were virus-specific with respect to WNV and Influenza. The phenotype of the cells which mediated cytotoxicity was Thy 1+, Lyt 2+ and L3T4-; however an L3T4+ helper population was required for the optimal generation of the cytotoxic response in vitro.

Resistance to cutaneous leishmaniasis in nude mice injected with L3T4+ T cells but not with Ly-2+ T cells

The importance of T cells in resistance to infection with the intracellular protozoan parasite Leishmania major is substantiated by the susceptibility to infection of athymic nude mice of both resistant and susceptible strains. However, the relative roles of different T cell subpopulations remain controversial. In order to address this issue, selected L3T4+ Ly-2- or L3T4- Ly-2+ T cell subpopulations from normal mice were adoptively transferred into athymic nude recipients of the same strain, and their capacity to mediate host-protective immunity against infection with L. major promastigotes was determined. In experiments with mice of different inbred strains, reconstitution with L3T4+ Ly-2- cells rendered the nude mice completely resistant to cutaneous leishmaniasis, whereas L3T4- Ly-2+ cells failed to do so. Partial protection in some recipients of large numbers of Ly-2+ cells could be ascribed to contamination of the transferred inoculum with L3T4+ cells. Thus, resistance to L. major infection in reconstituted nude mice can be promoted by L3T4+ T cells in the absence of detectable Ly-2+ T cells.

Mechanisms for recognition of tumor antigens and mediation of anti-tumor effect by noncytolytic Lyt-2+ T cell subset

The mode of anti-tumor function in vivo of noncytolytic Lyt-2+ T cells from C3H/He mice hyperimmune to syngeneic MH134 hepatoma was investigated in a double diffusion chamber system which was recently established in our laboratory. C3H/He mice were implanted intraperitoneally with the double diffusion chamber unit in which each chamber contained either L3T4+ T cell-depleted MH134-hyperimmune spleen cells plus mitomycin C-treated MH134 tumor cells or other syngeneic X5563 viable tumor cells plus normal spleen cells as a source of macrophages. Inclusion of anti-MH134 Lyt-2+ T cells together with MH134 tumor cells in one chamber resulted in comparable growth inhibition of viable X5563 tumor cells in the other chamber to that obtained by unfractionated MH134-hyperimmune spleen cells. The induction in the Lyt-2+ T cell-containing chamber of anti-tumor effect to be delivered into the other chamber was dependent on the co-existence of Ia-positive adherent cells along with Lyt-2+ T cells. Although adherent cell-depleted Lyt-2+ T cells regained the inducibility of anti-tumor immunity when supplemented with splenic adherent cells, the addition of adherent cells pretreated with chloroquine failed to restore the ability of Lyt-2+ T cells to induce their anti-tumor effect. In addition, paraformaldehyde-treated MH134 tumor cells instead of untreated tumor cells were not capable of activating Lyt-2+ T cells. These results indicate that a portion of Lyt-2+ T cells exerts their anti-tumor effect by a mechanism distinct from direct tumor cell lysis and that their activation for mediation of this type of tumor immunity requires the recognition of tumor antigens processed and presented by Ia-positive adherent cells.

Distinct epitopes recognized by I-Ad-restricted T-cell clones within antigenic site E on influenza virus hemagglutinin

A total of 14 I-Ad-restricted helper T-cell clones specific for the hemagglutinin (HA) molecule of influenza virus were isolated from spleens of BALB/c or (BALB/c X C57BL/10)F1 mice immunized with the H3 subtype influenza virus A/Memphis/71 (Mem 71) and from lymph nodes of BALB/c mice primed with purified HA. The specificity of these T-cell clones was assessed in proliferation assays by reactivity with naturally occurring strains of viruses that arose by antigenic drift and contain known amino acid sequence changes in HA and with a panel of monoclonal antibody (MAb)-selected mutants of Mem 71 with single amino acid substitutions in HA. The HA genes of those mutant viruses that failed to stimulate one or more of the T-cell clones were sequenced. The clones could be allocated to at least four groups, each group having a distinct pattern of reactivity with the panel of natural field strains. The epitopes recognized by the four groups of clones were found, by reactivity with MAb-selected mutants, to be in very close proximity to one another and probably overlapping. All of the distinct epitopes recognized by the T-cell clones were adversely affected by a single amino acid substitution, either at residue 60 or at residue 63 in the HA1 polypeptide chain, within the region known from antibody-binding studies as site E. Some, but not all, of the epitopes may be influenced by the addition of a carbohydrate side chain to the HA of a particular MAb-selected mutant and certain field strains containing an Asp----Asn substitution at residue 63. Site E is therefore a major site of H-2d helper T-cell recognition on the H3 HA.

Mediation of in vivo tumor-neutralizing activity by Lyt-2+ as well as L3T4+ T cell subsets

The present study reexamines the cell surface nature of T cells mediating in vivo protective tumor immunity with the use of anti-L3T4 and -Lyt-2 antibodies. C3H/HeN mice hyperimmune against syngeneic MH134 hepatoma or MCH-l-Al fibrosarcoma were prepared by intradermal (id) inoculation of viable tumor cells followed by surgical resection of the tumor and by repeated challenges with viable tumor cells. Spleen cells from these mice were fractionated into L3T4+ or Lyt-2+ T cell subset by treatment with anti-Lyt-2 or -L3T4 antibody plus complement (C). Winn assays performed by utilizing such fractionated T cells have revealed that both L3T4+ and Lyt-2+ T cell subsets from hyperimmune mice produced complete tumor protection. Flow microfluorometry study illustrated that the treatment with anti-L3T4 or -Lyt-2 antibody plus C resulted in the complete isolation of L3T4- Lyt-2+ (Lyt-2+) or L3T4+ Lyt-2- (L3T4+) T cell subset, respectively. This contrasted with the failure of treatment with anti-Lyt-1 antibody plus C to isolate all T cells expressing Lyt-2 marker. It was further demonstrated that each subset of T cells exerted its anti-tumor effect in a tumor-specific way and without a requirement for the other alternative subpopulation of unprimed T cells. These results indicate that Lyt-2+ T cell subset can be successfully isolated by treatment with anti-L3T4 but not with anti-Lyt-1 antibody plus C, and that each single subset of Lyt-2+ and L3T4+ T cells can function as in vivo effector T cells.

Mycobacteria-reactive Lyt-2+ T cell lines

The biological activities of mycobacteria-reactive Lyt-2+ T cells were characterized in vitro. T cells from mice immunized with killed Mycobacterium tuberculosis or viable M. bovis were restimulated in vitro and cloned under limiting dilution conditions. Several L3T4-Lyt-2+ T cell lines, some of them KJ16+, were established. These T cell lines were capable of lysing mycobacteria-primed macrophages in an antigen-specific way. The cytolytic activity of some T cell lines was found to be class I restricted, whereas others showed antigen-specific killing in the absence of apparent H-2 restriction. Several T cell lines produced interferon-gamma after appropriate stimulation. Furthermore, these T cell lines could induce tuberculostatic macrophage capacities by apparently two different mechanisms, namely by secretion of lymphokines (most probably interferon-gamma) and by direct cell contact. We conclude that CD8 T cells with antigen-specific cytolytic potential are generated during tuberculosis and that these T cells are involved in the immune response to tubercle bacilli.

L3T4 and the immunoglobulin gene superfamily: new relationships between the immune system and the nervous system

L3T4 is a mouse cell surface protein expressed on most thymocytes and on the subset of mature T cells that recognizes class II MHC molecules. Its primary function on T cells is most likely that of increasing the avidity of the interaction between T cells and antigen-presenting or target cells. It may accomplish this by binding to a nonpolymorphic region on class II MHC molecules. The cDNA and gene encoding L3T4 have been isolated and sequenced. Analysis of the amino acid sequence predicted by the nucleotide sequence indicates that L3T4 is a member of the Ig gene superfamily. It is most closely related to Ig and Tcr V regions. Although the amino-terminal domain of L3T4 is the portion of the molecule that is most similar to V-regions, L3T4 is one of the polydomain members of the Ig gene superfamily. Studies of the expression of L3T4 mRNA in various tissues led to the surprising finding that this gene is transcribed not only in T lymphoid cells, but also in brain. The predominant form of L3T4 mRNA expressed in brain is foreshortened as compared to that in T lineage cells, and it is most likely the product of a distinct transcriptional start site. If translated, the protein encoded by this brain transcript would be 217 amino acids in length and would lack the signal peptide and the amino-terminal 214 amino acids of the mature protein. It is not known whether a stable protein product is synthesized from this mRNA or what its function might be. However, these findings place L3T4 in an intriguing class of Ig gene superfamily members characterized by coexpression in the immune system and the nervous system.

Epitopes associated with MHC restriction site of T cells. III. I-J epitope on MHC-restricted T helper cells

I-J epitopes were found to be associated with the functional site of the class II MHC-restricted helper T (Th) cells: Virtually all of the H-2k-restricted Th cell function of H-2kxbF1 T cells was inhibited by the anti-I-Jk mAb, leaving the H-2b-restricted function unaffected. The I-Jk epitope was inducible in Th cells of different genotype origin according to the environmental class II antigens present in the early ontogeny of T cells. Although above results suggested that I-J is the structure reflecting the inducible MHC restriction specificity, further studies revealed some interesting controversies: First, the I-J phenotype did not always correlate with the class II restriction specificity, e.g., I-Ab-restricted Th from 5R was I-Jk-positive, whereas I-Ak-restricted Th of 4R was not. Second, there was no trans expression of parental I-J phenotypes and restriction specificities in F1 Th, e.g., the I-J phenotype was detected only on I-Ab-restricted Th of (4R X 5R)F1, whereas it was absent on I-Ak-restricted Th. This strict linkage between the restriction specificity and I-J phenotype was also found on Th cells developed in bone marrow chimera constructed with intra-H-2-recombinant mice. The expression of I-Jk was always associated with the restriction specificity of the relevant host. Thus, the restriction specificity of Th cells followed the host type, and the I-J expression on Th was exactly the same as that expressed by the host haplotype. These results indicate that I-J is an isomorphic structure adaptively expressed on Th cells that is involved in the unidirectional regulatory cell interactions, and that the polymorphism cannot be explained merely by the restriction specificity of the conventional T cell receptor heterodimer.

Coaggregation of the T-cell receptor with CD4 and other T-cell surface molecules enhances T-cell activation

The CD4 molecule, expressed by T cells restricted by class II major histocompatibility complex (MHC) molecules, is believed to play a role in T-cell activation. We have previously suggested that CD4 interacts with the T-cell receptor for antigen (TCR) and with class II MHC and that this dual interaction stabilizes the bond between the TCR and antigen in association with MHC. To investigate the contribution of CD4-TCR interaction, we have used the murine monoclonal anti-TCR V beta 8 antibody F23.1 to activate cloned T cells. Weak activation by soluble biotinylated F23.1 was markedly enhanced by crosslinking with either avidin or with anti-immunoglobulin (anti-Ig). The monoclonal anti-L3T4 antibody GK1.5, which normally inhibits the activation induced by F23.1, did not inhibit when GK1.5 and F23.1 were coaggregated on T cells by anti-Ig, and in many experiments activation was enhanced. Coaggregation of anti-Thy-1.2, anti-H-2Kk, or anti-LFA-1 with F23.1 also enhanced T-cell activation, although, unlike GK1.5, these antibodies in soluble form had no effect on the response to F23.1. These results are consistent with a model for T-cell activation that proposes a primary interaction between L3T4 and the TCR to stabilize TCR complexes and so to enhance T-cell activation. A related but less specific accessory role for other T-cell surface molecules is also suggested. We propose that the cellular interaction that leads to physiological T-cell activation not only achieves TCR ligation but also promotes through their ligation or redistribution the interaction of other T-cell surface molecules, all of which contribute to the overall strength of the activation signal.

Interstitial pneumonitis and hepatitis after transfer of bone marrow cells bearing the lpr gene to irradiated recipients: a disease due to large granular leucocytes?

Mice bearing the 'auto-immune' lpr gene develop a lympho-proliferative disease associated with the production of various antibodies. Lethally irradiated recipients were grafted with bone marrow cells (BMC) from syngeneic mice with or without the lpr gene. After 6 months, the survivors were 0/24 and 16/20 for the recipients of lpr and normal BMC respectively. The mortality rate was independent of the presence of T lymphocytes among the BMC. Histological evaluation showed that hepatitis, interstitial pneumonitis, and sclerosis of lymphohaemopoietic organs were the major causes of death for the recipients of lpr BMC. Hepatitis was associated with an increase in the number of liver interstitial cells (LIC) from about 2 X 10(6) up to about 10(7) cells per liver. The LIC associated with the hepatitis were composed of polymorphonuclear leucocytes and large mononuclear leucocytes, showing phenotypic (i.e. Thy.1+, asialo GM1, presence of cytoplasmic granules) and functional (i.e. non-phagocytic and cytolytic) properties of NK cells. The disease can be distinguished both from the spontaneous disease of the lpr mice (by the absence of 'lpr cells' and of anti-DNA antibodies) and from graft versus host disease by the absence of cutaneous and intestinal lesions. It may represent a model of tissue injury mediated by large granular leucocytes.

Effective clearance of a persistent viral infection requires cooperation between virus-specific Lyt2+ T cells and nonspecific bone marrow-derived cells

The lifelong chronic lymphocytic choriomeningitis virus (LCMV) infection established in neonatally or congenitally infected mice can be eliminated by adoptive transfer of lymphoid cells from LCMV-immune mice. In this study, we have identified the effector cells mediating the clearance of persistent and disseminated LCMV infection. Using mice that are recombinant in the H-2 region and by selective depletion of lymphocyte subpopulations, we show that viral clearance was mediated by LCMV-specific Lyt2+ L3T4- T cells that are restricted to the class I genes of the major histocompatibility complex. In addition, our results show a requirement for host-derived bone marrow cells for the effective elimination of virus from the liver. These studies emphasize the importance of virus-specific T cells and an intact bone marrow function in viral clearance.

Xenogeneic recognition of soluble and cell surface HLA class II antigens by proliferative murine T cells

In order to characterize the murine anti-human xenogeneic mixed lymphocyte reactions (MLR), we studied T cell proliferative responses against various human lymphoid cells by immunization of mice either with cellular or purified HLA-DR antigens. Data presented here indicated that small amounts of soluble HLA-DR antigen were able to prime mice, and that the xenogeneic MLR depends on the expression of HLA class II antigens on the stimulating cells. Experiments using a mutant cell line clearly showed that HLA-DP molecules were also sufficient in eliciting a primary or a secondary xenogeneic MLR while no secondary proliferative response was obtained with cells expressing only HLA class I molecules. Using a large panel of human cells with various haplotypes, our results also showed that (a) nonpolymorphic determinants of HLA class II antigens trigger dominantly the murine T cells and (b) the xenogeneic response required I-E and L3T4 accessory molecules and was not inhibited with anti I-A and monomorphic anti-HLA class II antigen monoclonal antibodies. Altogether these results suggest that HLA class II antigens act as nominal antigens in triggering a murine anti-human proliferative response.

Increased expression of major histocompatibility complex antigens on lymphocytes from aged mice

Many studies have reported age-related changes in immune responses that could be due to alterations in lymphoid cell numbers or functions. Here we report the results of studies using immunofluorescent staining and in vitro assays of cellular function to compare the expression of cell surface antigens on lymphocytes from mice up to 2 years of age. No significant changes were observed in the frequencies of spleen cells bearing class I or class II major histocompatibility complex (MHC) antigens, surface immunoglobulin, or Thy-1, Ly-1, Ly-2, or L3T4 antigens. However, the densities (per cell) of both class I and class II MHC antigens were increased significantly on cells from aged as compared to young mice, whereas the densities of the other cell surface antigens studied were unchanged or slightly decreased. The increased levels of MHC antigen expression in old relative to young mice were shown to be functionally significant regarding immunological stimulation. These data suggest that T-cell clones silent in young individuals may be activated in comparable situations in older animals, leading to immunological alterations perhaps including increased autoreactivity.

Structure of the mouse gene encoding CD4 and an unusual transcript in brain

The T-cell differentiation antigen CD4 plays an important role in the function of T cells that recognize class II major histocompatibility complex proteins. Mouse CD4 (L3T4) has previously been shown to be evolutionarily related to immunoglobulin variable regions based on the predicted protein sequence from cDNA clones. The gene encoding L3T4 was found to be transcribed not only in a subset of T-lineage cells but also unexpectedly in brain, where a shorter transcript was found. In the present study the gene encoding L3T4 is shown to span 26 kilobases and to contain 10 exons. The structural organization is similar to that of other members of the immunoglobulin gene superfamily except for the striking presence of an intron in the middle of the sequence encoding the amino-terminal immunoglobulin-like homology unit. The structure of the shorter L3T4 transcript in mouse brain has been determined. This mRNA appears to be generated from a transcriptional start site within the coding sequence in exon VI. If translated, this transcript would encode a protein of 217 amino acids that lacks the usual L3T4 signal peptide and the amino-terminal 214 amino acids of the mature protein.

Two types of mouse helper T cell clone. III. Further differences in lymphokine synthesis between Th1 and Th2 clones revealed by RNA hybridization, functionally monospecific bioassays, and monoclonal antibodies

Lymphokine synthesis patterns of a panel of 19 T cell clones have been evaluated, using mRNA hybridization methods to examine 11 different mRNAs induced by Con A. The two types of CD4+ Th cell clone described previously were clearly distinguished by this procedure, and the differences between the two types have now been extended to six induced products. With minor exceptions, only Th1 clones synthesized mRNA for IL-2, IFN-gamma, and lymphotoxin, and only Th2 clones synthesized mRNA for IL-4, IL-5, and another induced gene, P600. Four more induced products were expressed preferentially but not uniquely by one or another type of clone: mRNAs for GM-CSF, TNF, and another induced, secreted product (TY5) were produced in larger amounts by Th1 clones, whereas preproenkephalin was preferentially expressed by Th2 clones. IL-3 was produced in similar amounts by both types of clone. mAbs were used to establish three bioassays that were functionally monospecific for IL-2, IL-3, and IL-4, and a new anti-IFN gamma mAb, XMG1.2, was used to establish an ELISA for IFN-gamma. These four assays were used to show that secreted protein and mRNA levels correlated well for all cell lines. The implications of these findings for normal T cells are discussed.

The cellular basis for the Ia restriction in murine experimental autoimmune thyroiditis

Susceptibility to experimental autoimmune thyroiditis (EAT) in the mouse is linked to the I-A subregion of the major histocompatibility complex. EAT can be induced in susceptible strains of mice by immunization with mouse thyroglobulin (MTg) and adjuvant. We have described a cell transfer system wherein spleen cells from EAT-susceptible CBA/J mice primed in vivo with MTg and lipopolysaccharide (LPS) can be activated in vitro with MTg to transfer EAT to naive syngeneic recipients. This cell transfer system was used to elucidate the cellular basis for the I-A restriction in EAT. While the cell active in transferring EAT was Thy 1+ I-A-, depletion of I-A+ cells from the in vitro culture prevented the activation of EAT effector T cells. MTg-pulsed mitomycin C-treated naive syngeneic spleen cells as antigen-presenting cells (APCs) could replace the I-A+ cells in vitro. Allogeneic (Balb/c) APCs were ineffective. Using APCs from several recombinant inbred strains of mice, it was shown that C3H/HEN and B10.A(4R) APCs were effective in activating MTg/LPS-primed CBA/J spleen cells to transfer EAT while B10.A(5R) APCs were ineffective. This maps the H-2 restriction to the K or I-A subregions. Addition of polyclonal anti-Iak or monoclonal anti-I-Ak or anti-L3T4 during in vitro activation inhibited both the generation of EAT effector cells and the proliferative response to MTg. Irrelevant anti-Ia reagents, monoclonal anti-I-Ek, and monoclonal anti-I-Jk were ineffective. Thus the I-A restriction in murine EAT appears to result from an I-A restricted interaction between Ia+ APCs and Ia- EAT effector T cells.

Ability of fixed B-lymphoma cells to present foreign protein antigen fragments and allogenic MHC molecules to a cloned helper-T-cell line

Cloned, L3T4+ T cells have been shown to respond to foreign protein antigens in the context of self-Ia glycoproteins and to non-self Ia glycoproteins. In the case of responses to foreign proteins, fixed antigen-presenting cells can present antigen fragments, but cannot present native proteins. Whether fixed allogenic cells can stimulate has been controversial. We have examined this question using a dual-reactive cloned helper-T-cell line. We find that conditions of fixation that block the presentation of native antigen to this cloned line, but which allow the presentation of antigen fragments, also allow presentation of allogeneic Ia molecules, leading to stimulation of the cloned line. This study also revealed an occult alloreactivity in the cloned T-cell line, which was expressed by fixed, but not by normal, antigen-presenting B lymphoma cells. All of these stimuli proceeded via the same clonotypic receptor, as determined by blocking with anti-T-cell receptor monoclonal antibody. These data suggest that responses to non-self Ia glycoproteins involve direct recognition of the allogeneic Ia molecules and do not require processing and presentation of these antigens by self Ia molecules.

Effect of antigen priming on T-cell suppression. I. Activity of Ly 1+2+ feedback suppressor T-cell precursors after isolation from competing Ly 2-T cells

Previous experiments have demonstrated that feedback suppression of murine antibody responses occurs in vitro after exposure of unprimed T-cell subsets to suppression-inducing signals from primed cells, resulting in suppression of primary and secondary IgM as well as IgG anti-SRBC responses. However, following priming with antigen when cells appear which are capable of inducing feedback suppression, the ability of unfractionated splenic T-cell populations to mediate detectable feedback suppression in vitro rapidly disappears, suggesting that priming alters the expression of feedback suppression at the same time as providing for its induction. In the present study, we have succeeded in isolating active feedback suppressor T-cell precursors (preTs) in the Ly 1+2+ and L3T4- T-cell populations from SRBC-primed as well as from unprimed mice, demonstrating that preTs are not lost after priming. The preTs isolated from primed mice resemble those isolated from unprimed mice in Ly and L3T4 phenotype, cell dose requirements, kinetics, level of suppression, and requirement for in vitro activation by primed cells. These results imply that antigen priming neither significantly depresses nor enhances the ability of Ly 1+2+ preTs to participate in feedback suppression and that activated suppressor effector cells are not detectable in the Ly 1+2+ splenic T-cell subset. Priming does, however, induce an enhancing activity in Ly 2-, L3T4+ T cells which appears to compete with feedback suppression and thus may account for the absence of detectable feedback suppression when unfractionated T cells from primed mice are the only source of preTs.

Reactive lymphocytes in lacrimal gland and vasculitic renal lesions of autoimmune MRL/lpr mice express L3T4

The lacrimal gland inflammatory lesions and renal vasculitic lesions of autoimmune MRL/lpr mice were analyzed for the lymphocyte subsets present. The majority of cells were Thy-1.2+ T cells (mean, 85%) of the L3T4+ helper T phenotype (mean, 64 and 58%, respectively). Lesser numbers of Lyt-2+ suppressor/cytotoxic T cells, B cells, and macrophages were present. The finding that the majority of lymphocytes in both the lacrimal gland inflammatory lesions and renal vasculitis of MRL/lpr mice expressed L3T4 suggests that these cells may be capable of responding to antigen presentation and that an active immunologic response occurs at these sites.

Effector cells in allelic H-2 class I-incompatible skin graft rejection

The cellular mechanisms of skin graft rejection with allelic H-2 class I differences were studied by examining the effect on graft survival of in vivo administration of anti-Lyt-2.2 mAb, anti-L3T4 mAb, or both to recipient mice. The injections of anti-Lyt-2.2 mAb and anti-L3T4 mAb caused selective depletions of Lyt-2+ cells and L3T4+ cells, respectively. Injection of anti-Lyt-2.2 mAb significantly prolonged graft survival in 7 of 12 combinations of H-2D-end difference, but did not prolong graft survival in 5 other combinations of H-2D-end difference, or in 2 combinations of H-2K-end difference. Injection of anti-L3T4 mAb did not prolong graft survival in any combinations with class I difference tested. Injection of anti-L3T4 mAb plus anti-Lyt-2.2 mAb markedly prolonged graft survival in the combinations with class I difference in which anti-Lyt-2.2 mAb had no effect and overcame the effect of anti-Lyt-2.2 mAb in those in which anti-Lyt-2.2 mAb had an effect in prolonging graft survival. These results indicated that in combinations in which anti-Lyt-2.2 mAb did not prolong graft survival, class I antigen stimulated L3T4+ effector cells when Lyt-2+ cells were blocked and Lyt-2+ effector cells when L3T4+ cells were blocked. On the other hand, in the combinations in which anti-Lyt-2.2 mAb prolong graft survival, these antigens initially caused preferential stimulation of Lyt-2+ but not L3T4+ effector cells, although delayed activation of L3T4+ effector cells occurred when Lyt-2+ cells were blocked. Furthermore, a significant correlation was found between the effect of anti-Lyt-2.2 mAb in prolonging graft survival and the failure of recipient mice to produce H-2 antibody. These results can be taken as evidence that L3T4+ effector cells are not involved in the initial phase of graft rejection in these combinations.