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

A role for IFN-gamma and NK cells in immune responses to T cell-regulated antigens types 1 and 2

Responses to antigens that have been previously recognized as T cell-independent are now known to be dependent on some form of T-cell (or T cell-derived) help. This T-cell dependency, however, can be most easily noted when responses to small resting B cells are examined, since responses of larger, size-separated B cells to TNP-Ficoll require little if any T-cell help. The type of ancillary "help" that is required for the responses to type 1 and type 2 antigens exhibits certain similarities as well as differences. Thus, responses to both of these antigens can be stimulated in the presence of L3T4- or L3T4+ cells as well as in the presence of IL2. However, while the presence of IFN-gamma may be significantly inhibitory for the responses to the type 2 antigen TNP-Ficoll, they do not appear to influence the response to the type 1 antigen TNP-BA. Furthermore, while vigorous elimination of NK cell activity from purified B-cell populations enhances the response to TNP-Ficoll, it has no discernible effect on the response to TNP-BA. These results suggest that determination of type 1 and type 2 antigens may be made not only based on the characteristics of the carrier molecule but also on the nature of ancillary help that needs to be provided for these antigens to stimulate optimal responses. Type 1 antigens have polyclonal B-cell activating properties and stimulate responses which are not influenced by IFN-gamma, type 2 antigens have no polyclonal B-cell activating properties and stimulate responses which can be influenced by IFN-gamma.

Characterization of Lyt-2-, L3T4- class I-specific cytolytic clones in C3H-gld/gld mice. Implications for functions of accessory molecules and programmed development

We report the first demonstration of Thy-1+, Lyt-2-, L3T4- MHC-specific CTL clones derived from the Lyt-2-, L3T4- subset of lymph node cells of C3H-gld/gld mice. These clones express alpha/beta heterodimeric TCRs on the cell surface and specifically recognize class I molecules on target cells. Lyt-2 and L3T4 molecules are therefore not essential for the induction, recognition, and killing of antigen-specific CTL. In addition, these studies suggest that antigen specificity development for class I structures may occur before Lyt-2 gene activation in the differentiation of T cells.

CD8-positive T lymphocytes specific for murine cytomegalovirus immediate-early antigens mediate protective immunity

We have shown in a murine model system for acute, lethal cytomegalovirus (CMV) disease in the immunocompromised natural host that control of virus multiplication in tissues, protection from virus-caused tissue destruction, and survival are mediated by virus-specific CD8+ CD4-T lymphocytes. Protection from a lethal course of disease did not result in a rapid establishment of virus latency, but led to a long-lasting, persistent state of infection. The CD8- CD4+ subset of T lymphocytes was not effective by itself in controlling murine CMV (MCMV) multiplication in tissue or essential for the protective function of the CD8+ CD4- effector cells. The antiviral efficacy of the purified CD8+ CD4- subset was not impaired by preincubation with fibroblasts that presented viral structural antigens, but was significantly reduced after depletion of effector cells specific for the nonstructural immediate-early antigens of MCMV, which are specified by the first among a multitude of viral genes expressed during MCMV replication in permissive cells. Thus, MCMV disease provides the first example of a role for nonstructural herpesvirus immediate-early antigens in protective immunity.

Age-related changes of splenic T cells in mice--a flow cytometric analysis

Splenic T cells of C57BL/6 mice, ranging in age from newborn to 24 months old, were examined by two-colour flow cytometry using monoclonal antibodies (moAbs) to Thy-1, Lyt-1, Lyt-2 and L3T4. Thy-1+ cells in the spleen increased gradually after the birth, and reached a plateau around at 3 months of age, but did not show a significant age-related decline even at 24 months of age. Lyt subpopulations of T cells (Lyt-1+2+, Lyt-1+2-, Lyt-1-2+) showed a proportional increase until 1 month of age, but the onset of their imbalance was observed as early as 3 months of age. The percentage of L3T4+ subpopulation stayed at a relatively constant level throughout life (approx. 55%). At the individual cell level, Lyt-2 antigen was most vulnerable to aging and its membrane surface density showed a prominent decrease in 24-month-old T cells. An apparent decline was observed in the mitogen reactivity and cell-mediated cytolytic T lymphocyte (CTL) activity of old T cells or their subpopulations which were purified by the cell sorter.

Control of prothymocyte proliferation by thymic accessory cells

All thymocyte subpopulations derive from intrathymic precursors which are double negative (DN) for Lyt-2 and L3T4 differentiation antigens. Although nearly half of DN cells express a receptor for interleukin 2 (IL 2R), they respond poorly to IL 2. DN cell proliferation can be obtained in the presence of various exogenous stimuli, but the in vivo signal for DN cell response to IL 2 remains unclear. We show in the present report that phagocytic cells of the thymic reticulum are able to induce the proliferation of DN thymocytes in the presence of recombinant IL 2 (rIL 2). Cell-to-cell contact is needed for this effect. Antibodies directed against class I MHC antigens but not against class II can inhibit DN cell proliferation. DNA-synthetizing cells were labeled by incubation with 10 microM bromodeoxyuridine either before or at various times during the culture period. Bromodeoxyuridine was then detected in the DNA of proliferating cells and/or their progeny already stained with anti-Lyt-2 and L3T4 antibodies. During the initial 16 h and independently of culture conditions, 16-25% of the cells expressed surface antigens and 50-65% of them derived from DN cells which were in S phase just before culture; these differentiated cells had a very short life span. In the second culture period, the presence of both rIL 2 and thymic accessory cells was necessary for cell survival. In these conditions, DN cell number and proliferation rate were constant and a low number of Lyt-2+ and/or L3T4+ cells was continuously generated. Thymic accessory cells therefore appear to provide the signal(s) necessary for IL 2-induced proliferation of thymocyte precursors. Implications of these findings for normal in vivo intrathymic proliferation and differentiation are discussed.

Deterioration of cellular immunity during aging. The relationship between age-dependent impairment of delayed-type hypersensitivity reactivity, interleukin-2 production capacity, and frequency of Thy-1+,Lyt-2- cells in C57BL/Ka and CBA/Rij mice

The effect of aging on the delayed-type hypersensitivity (DTH) to sheep red blood cells (SRBC) in vivo and the interleukin-2 (IL-2) production capacity in vitro by spleen cells from young (17 weeks) and old (125 weeks) CBA/Rij and C57BL/Ka mice were investigated. For both CBA/Rij and C57BL/Ka mice an age-related decline in the DTH response to SRBC and the IL-2 production capacity was observed. Both parameters are mediated by Thy-1+,Lyt-2- spleen cells. For both mouse strains the proportion of Thy-1+,Lyt-2- spleen cells declined less strongly with aging than the DTH reactivity and the IL-2 production capacity. From this it was concluded that not only a quantitative but also a qualitative decrease of T-cell function occurs during senescence. It was also investigated whether the proportion of Thy-1+,Lyt-2- peripheral blood lymphocytes can be used as a predictive value with regard to the decline of DTH with aging of the corresponding mouse. This was indeed found to be the case in CBA/Rij mice, but not in C57BL mice.

Reconstitution of MHC class I specificity by transfer of the T cell receptor and Lyt-2 genes

The T cell receptor alpha and beta chain genes donated by an H-2 class I-specific, CD8-dependent cytotoxic T cell clone were transferred, alone or in combination with the Lyt-2 gene, into a class II-restricted, CD4+ T cell hybridoma. Two important points emerged. First, the alpha and beta T cell receptor genes endowed the recipient with the H-2 class I specificity of the donor only if the same cell had also been transfected with the Lyt-2 gene. Second, the functional Lyt-2 molecule was expressed on the transfected cells in the absence of the Lyt-3 polypeptide. These results demonstrate that, besides the T cell receptor, the Lyt-2 polypeptide is the only subset-specific molecule required to retarget a class II-reactive, CD4+ T cell line toward H-2 class I molecules.

Recognition requirements for the activation, differentiation and function of T-helper cells specific for class I MHC alloantigens

The present review has focused on the specificity of the T-helper cell populations initiating MHC class I alloreactions. In contrast to conventional immune responses against soluble antigens, responses against membrane-bound class I alloantigens are initiated by two distinct antigen-specific T-helper cell populations that can be distinguished by their Lyt phenotype, MHC restriction specificity, antigen specificity, and requirement for thymically determined self-recognition. Alloresponses were shown to be a composite consisting of two distinct components: one mediated by L3T4+ Th cells and very similar to conventional self + X responses; and one mediated by Lyt2+ Th cells and unique to alloresponses against MHC class I antigens. As would befit an unusual Th cell population, the recognition/response spectrum of Lyt2+ Th cells was highly unusual and was found to be the basis for much of the uniqueness we attribute to immune alloreactions, including rapid rejection of tissue allografts in vivo.

Coclustering of CD4 (L3T4) molecule with the T-cell receptor is induced by specific direct interaction of helper T cells and antigen-presenting cells

Blocking studies with monoclonal antibodies have suggested that helper T cell recognition and triggering involve the CD4 (L3T4) accessory molecule as well as the T-cell receptor (TCR) that is linked to the T3 complex. We have investigated the surface distribution of L3T4 and TCR during the direct interaction of a cloned murine helper T-cell line with an antigen-presenting B-cell line. Using immunofluorescence microscopy, we show that in 1:1 cell couples formed between the two cells, in which a specific interaction can be demonstrated, the L3T4 and the TCR become redistributed on the T-cell surface so that they are concentrated in the cell-cell contact region. This coclustering of L3T4 with TCR occurs only when the relevant antigen and appropriate major histocompatibility class II molecules are presented to the T cell, and it therefore requires the specific interaction of the TCR with its complex ligand on the antigen-presenting cell.

CD4 monoclonal antibody pairs for immunosuppression and tolerance induction

A pair of rat anti-mouse CD4 monoclonal antibodies (mAb) have been selected which bind to different epitopes of the molecule. Both the mAb are rat IgG2b and show clear synergistic activity in complement lysis in vitro. When injected together in vivo, they exhibit an improved immunosuppressive effect, compared to each antibody alone, on allogeneic graft rejection, humoral responses and on tolerance induction. Limiting dilution analysis indicates that the in vivo depletion of interleukin 2-producing cells is improved using both mAb by 2-3-fold over that obtained with the individual antibodies. As little as 60 ng per mouse of the CD4 antibody pair was sufficient to allow the induction of tolerance to human gamma-globulin, even without elimination of the CD4+ cells. The results suggest that appropriate antibody pairs may be good candidates for effective immunosuppressive serotherapy in man.

T-cell receptor genes in autoimmune mice: T-cell subsets have unexpected T-cell receptor gene programs

Two unique cell subsets have been identified in the autoimmune-prone MRL/MP lpr/lpr and C3H/HeJ gld/gld murine strains that have the Lyt-2-,L3T4-,Thy-1+, and Lyt-2-,L3T4-,Ia-,Thy-1- phenotypes, respectively. We have now found that these cells express T-cell receptor proteins on their surface. Our observations further indicate that the expression of the Thy-1 antigen does not correlate with the expression of alpha-chain and beta-chain T-cell receptor polypeptides. Interestingly, T-cell receptor gamma-chain RNA expression may be influenced or correlate with Thy-1 molecular expression. These studies indicate unusual relationships of different cell-surface structures that may reflect unexpected developmental programs.

Islet allograft survival after a single course of treatment of recipient with antibody to L3T4

Allografts of pancreatic islets of Langerhans were induced to survive for an indefinite period in diabetic mice if, at the time of engraftment, the mice received a single course of treatment with a monoclonal antibody directed against the L3T4 determinant, a nonpolymorphic cell surface glycoprotein present on the cell surface of the murine T helper-inducer lymphocyte subset. This treatment allowed the survival of islets of Langerhans transplanted across a major histocompatibility barrier without additional immunosuppression. The results demonstrate that the lymphocyte subset defined by the expression of the L3T4 molecules is central to the induction of allograft rejection and provides a model for tolerance induction for organ allograft transplantation.

The immune response of the mouse to lymphocytic choriomeningitis virus. V. High numbers of cytolytic T lymphocytes are generated in the spleen during acute infection

In the spleens of C57BL/6J (B6) and CBA/J (CBA) mice undergoing acute infection with lymphocytic choriomeningitis (LCM) virus, lymphocytes with the ability to develop in vitro into LCM virus-specific cytolytic clones were enumerated by use of the limiting dilution method. At intervals after virus inoculation, defined numbers of cells were cultivated with virus-infected syngeneic stimulator cells and T cell growth factor in multiple wells of microculture plates. After 7 days, individual cell cultures were tested for their ability to cause release of 51Cr from infected and uninfected syngeneic target cells. In cultures seeded with spleen cells from uninfected mice or from mice infected 3 days previously, no cytolytic activity was observed. On day 5, cells developing into LCM virus-specific cytolytic effector cells were detected. They rose in numbers, and on days 8 to 9 after infection, values of approximately 1/10 and 1/200 in B6 and CBA mice, respectively, were calculated. A low proportion of microcultures proved cytolytic also for noninfected syngeneic target cells, but the counts thus released were consistently much lower than the counts set free from infected targets, and no regular dose-response relationships existed between seeded cells and positive cultures. Determination of cell surface antigens of responder cells by negative and positive selection procedures disclosed that they were predominantly T lymphocytes and expressed Lyt-2 but not L3T4 surface markers. Lysis by the great majority of LCM virus-specific clones was restricted by products of the major histocompatibility gene complex (MHC), but a few lysed, in addition, allogeneic infected or uninfected targets; however, a consistent pattern of alloreactivity was not observed. Furthermore, cells of a proportion of the cultures also lysed uninfected YAC cells. Probably this natural killer-like activity was acquired by T lymphocytes during prolonged cultivation. We conclude that most spleen cells that during acute infection with LCM virus attained the ability to develop in vitro into LCM virus-specific cytolytic clones were derived from MHC-restricted Lyt-2+, L3T4- antigen-specific cytolytic T lymphocytes and their activated precursors.

Cytotoxic T lymphocyte recognition of a xenogeneic major histocompatibility complex antigen expressed in transgenic mice

Introduction of a porcine major histocompatability complex (MHC) class I gene (PD1) into the genome of a C57BL/10 (B10) mouse has been shown to lead to cell surface expression of the porcine MHC antigen, SLAPD1 in a transgenic mouse. The PD1 product expressed on spleen cells from the transgenic mice stimulated B10 spleen cells in a mixed lymphocyte culture to generate PD1-specific cytotoxic T lymphocytes (CTL). The CTL were PD1 specific since they lysed transgenic splenic blast cells and PD1-transfected L cells, but not B10 blasts or control L cells. The CTL were L3T4-, Lyt-2+ and their activity was partially inhibited by either anti-Lyt-2 antibody or by anti-swine MHC alloantibodies. The repertoire of responding B10 anti-transgenic CTL was assessed by examining their cross-reactivity on a series of murine allogeneic targets. The B10 anti-transgenic CTL showed some cross-reactivity on conventional allogeneic targets, but reacted strongly on a series of mutant H-2Kbm blast cells. In addition, B10 anti-B6.cH-2bm6 CTL cross-reacted extensively on the transgenic target cells. These results demonstrated that normal B10 CTL possess a repertoire specific for the products of the xenogeneic class I gene PD1, that this repertoire is cross-reactive with the conventional alloreactive CTL repertoire, and that there exists an unanticipated relationship between PD1-specific CTL and CTL specific for Kb mutant determinants.

Class II antigen-specific murine cytolytic T lymphocytes (CTL). I. Analysis of bulk populations and establishment of Lyt-2+L3T4- and Lyt-2-L3T4+ bulk CTL lines

Murine allogeneic cytolytic T lymphocytes (CTLs), including long-term bulk CTL lines, were induced in I-region-incompatible combinations of strains in vitro in order to study the phenotypes of class II major histocompatibility complex (MHC) antigen-specific CTLs, as well as the possible functional involvement of accessory cell interaction molecules such as Lyt-2 and L3T4. This report shows that class II-specific allogeneic CTL populations consist of two types of T cells. Lyt-2+L3T4- (2+4-) and Lyt-2-L3T4+ (2-4+), in variable proportions depending on the strain combination, that in vitro bulk CTL lines with each of these phenotypes can be established, that the killing function of 2-4+ CTL is sensitive to the blocking effect of anti-L3T4 antibodies, suggesting functional involvement of this molecule in the CTL-target interaction, that anti-Lyt-2 antibodies fail to block killing by 2+4- cells, suggesting that such CTLs do not utilize this molecule in their killing function, and that while I-A-specific CTLs of both phenotypes are detectable, 2-4+ cells could not be detected among I-E-specific CTL populations.

Differences in Ly 2- L3T4- thymocytes from foetal and adult murine thymus

The thymus is the major site of mammalian T cell production. The exact steps which occur in the thymus and give rise to mature T cells have not been defined, but there is general agreement that the earliest T cells are included in the group of thymic lymphoid cells lacking Ly 2 (CD8) and L3T4 (CD4). This population represents 2-6% of adult thymocytes and the vast majority of thymocytes in the mouse embryo until about day 16 of gestation. It has often been assumed that the foetal and adult CD4- CD8- thymocytes are equivalent. This paper shows that there are significant differences between the CD4- CD8- cells from these sources, in that the adult includes at least two subsets which are undetectable in the embryo. These two subsets of CD4- CD8- cells are both Ly 1high, B2A2- and M1/69-; one is Thy 1+ and one is Thy 1-. Each represents 20-25% of adult CBA double negative thymocytes. Both these populations are excluded from analyses of CD4- CD8- thymocytes which have been further selected as Ly 1low, a procedure adopted in several studies of early thymocytes. Even those subpopulations of CD4- CD8- cells which appear to express similar markers in adult and embryo thymus are quite different when analysed for cell size (forward light scatter), with the embryonic forms being much larger.

Extraction and immunocytochemical characterization of viable mononuclear inflammatory cells from brains of mice with chronic Toxoplasma gondii infection

A method which combined mechanical and enzymatic dissociation of brain parenchyma with Percoll density gradient centrifugation of the resulting tissue suspension was developed for the extraction of viable mononuclear inflammatory cells from the brains of mice. This method was used to extract mononuclear inflammatory cells from the brains of normal mice and mice chronically infected with the intracellular parasite Toxoplasma gondii. Infection with T. gondii was found to result in a 5- to 7-fold increase in the number of mononuclear cells which could be extracted from mouse brains. Immunocytochemical characterization of the extracted mononuclear cell fractions using monoclonal antibodies against T cell subsets and monocyte/macrophages revealed that the numbers of helper T cells, cytotoxic/suppressor T cells, and monocyte/macrophages present in mouse brain increased markedly after infection with T. gondii. This method may prove useful in identifying the cells responsible for inhibition of growth of tumor cells in the brain which has been observed after infection with T. gondii in mice.

Adoptive transfer of murine autoimmune orchitis to naive recipients with immune lymphocytes

A protocol was developed for reproducibly transferring experimental autoimmune orchitis (EAO) to naive recipient mice. Cell donors were (C57BL/6 x A/J)F1 mice immunized about 14 days earlier with mouse testicular homogenate with Freund's adjuvant and an extract of Bordetella pertussis. Lymphocytes from lymph nodes and spleens were equally capable of transferring disease. As few as 5 X 10(6) cells were able to transfer EAO, which began on Day 5-7 after transfer. Infiltrate of lymphocytes and macrophages in the region of the rete testis and straight tubules was the most reproducible early lesion, suggesting that this is the initial site of T cell-antigen interaction. It was not necessary to use both Mycobacteria and B. pertussis adjuvants in donor immunization to achieve transfer of EAO. Disease transfer was antigen specific since only cells from donors immunized with TH could transfer disease. In vitro stimulation of the cells with testicular antigens and/or concanavalin A was a prerequisite to successful transfer of EAO, which was dependent on the presence of L3T4+ T cells since depletion of these cells greatly diminished EAO in recipients and the lymphocyte proliferation response to testicular antigens. Disease did not depend on an antibody response by the recipients. The results imply that effector cells, once generated by immunization and fully activated or selected by in vitro stimulation, can home to specific locations in the testis, locate relevant autoantigens, and cause disease.

Isolation and initial characterization of multiple species of T-lymphocyte subset cDNA clones

A modified differential screening procedure was applied to analyze cDNA libraries of cloned helper T lymphocytes (Th) and cytolytic T lymphocytes (CTL). Negative and positive differential screening and RNA blot analysis were used to identify cDNA clones that were expressed preferentially in Th or CTL. Seven clones corresponded to previously described T-cell genes, and 16 additional types of cDNA clones were isolated, 9 from Th and 7 from CTL. Of these, 3 were expressed in both Th and CTL, 7 were expressed in only Th, and 6 only in CTL. These clones were analyzed for induction after stimulation by interleukin 2 or Con A or after stimulation of the T-cell antigen receptor (TCR). Three different patterns of expression were seen: induction only by Con A, induction by Con A and interleukin 2, and induction by Con A and TCR stimulation. The approach is potentially useful for analyzing paths of T-cell differentiation and detecting cDNA clones encoding unrecognized cytokines.

Virus-lymphocyte interaction: T cells of the helper subset are infected with lymphocytic choriomeningitis virus during persistent infection in vivo

The lifelong persistence of lymphocytic choriomeningitis virus (LCMV) in neonatally or congenitally infected mice is accompanied by a suppression of virus-specific T-cell responses. In this study, we identified the subset of T cells infected with LCMV during persistent infection in vivo. Using specific monoclonal antibodies to separate the different lymphocyte cell populations and employing both an infectious center assay and immunofluorescence to detect the virus, we found that infection is confined primarily to T cells of the helper subset (L3T4+ Lyt2-), with minimal involvement of cytotoxic T cells (Lyt2+ L3T4-) and mature B cells. About 0.54 to 1.1% of L3T4+ T cells were producing the virus, as determined by the infectious center assay. In contrast, 9.1 to 12.2% of these L3T4+ T cells contained viral antigen, as shown by immunofluorescence studies. This finding suggested that, at any given time, a substantial number of infected T cells were not producing infectious virus. This infection of T helper cells may be involved in the suppression of LCMV-specific T-cell responses observed in persistently infected mice.

Regulation of IL 2 expression in mitogen-activated murine T lymphocytes

In mitogen-stimulated mouse spleen cells, the IL 2 gene is only transiently expressed with maximal mRNA steady state levels between 6-14 h post stimulation with Concanavalin A (Con A). This is also reflected by the kinetics of IL 2 release into culture supernatants. Con A-stimulated L3T4+ and Lyt2+ T cell subpopulations express the IL 2 gene and produce IL 2 similarly. The half-life of IL 2 mRNA is only 30 min, but can be prolonged significantly by cycloheximide. At later post stimulation times IL 2 gene transcription is reduced, as indicated by the reduced effect of cycloheximide. IL 2 gene expression is not influenced by added IL 2 or IFN-gamma.

Effective activation of resting mouse T lymphocytes by cross-linking submitogenic concentrations of the T cell antigen receptor with either Lyt-2 or L3T4

We studied the activation of small resting mouse T lymphocytes by antibodies to the T cell antigen receptor in combination with antibodies to other T cell surface antigens. Solid-phase but not soluble antibodies KJ16-133 and F23.1, both directed to beta chains of the V beta 8 family, activate T cells to proliferate in the presence of growth factors, in a dose-dependent fashion. Antibodies to Lyt-2 and to L3T4 had no activating effect at any concentration. However, submitogenic concentrations of KJ16-133 and of F23.1 synergized with a wide range of concentrations of anti-Lyt-2 and anti-L3T4 to cause T cell proliferation similar or greater in magnitude to that caused by high concentrations of anti-T cell receptor antibody. Synergistic activation was also observed with antibodies to Lyt-1, LFA-1 and H-2 class I antigens but to a significantly lower degree. This was particularly clear in limiting dilution experiments in which the corrected frequencies of T cells proliferating in response to low amounts of anti-T cell receptor antibody together with anti-Lyt-2 were 1/4 to 1/7 for BALB/c T cells. The frequencies of BALB/c T cells responding to high concentrations of anti-T cell receptor antibody alone were between 1/14 and 1/126 and still lower frequencies of T cells proliferated in synergistic responses with anti-LFA-1 or anti-Lyt-1. Synergistic activation leads to the induction of functional cytotoxic cells. We interpret these data as suggestive that cross-linking of the T cell antigen receptor with either Lyt-2 (CD8) or L3T4 (CD4) represents an optimal activating signal for resting T cells. We think that, in physiological T cell activation, cross-linking of the T cell receptor to CD8 or CD4 is induced by their simultaneous binding to major histocompatibility complex (MHC) class I (for CD8) or MHC class II (for CD4) molecules on stimulator cells. We consider the possibility that similar cross-linking requirements may also exist during T cell repertoire selection in ontogeny, thus accounting for the strict coexpression of MHC class I and class II-restricted T cell receptors with CD8 and CD4 molecules, respectively.

Regulation of cytolytic T-lymphocyte generation by B-cell stimulatory factor

The growth and differentiation of cytolytic T lymphocytes (CTL) is regulated by soluble growth hormones, of which interleukin-2 (IL-2) is considered to be of prime importance. Here we report that the lymphokine B-cell stimulatory factor (BSF-1 or interleukin-4) also has profound effects on the generation of these functionally active T cells. In particular, BSF-1 acts as a potent helper factor for the generation of CTL in primary mixed leukocyte culture (MLC) and induces cytolytic activity in in vitro primed, MLC memory populations. Direct comparison of purified recombinant BSF-1 and IL-2 reveals BSF-1 to be the more potent CTL helper factor in primary MLC. Interestingly, the two lymphokines differed in that IL-2, but not BSF-1, induced a lytic population in cultures of unprimed cells without an overt antigenic stimulus. Collectively, our data provide a direct demonstration of a heretofore undefined mechanism by which CTL activation and amplification can occur.

Monoclonal antibody analysis of skin in chronic murine graft vs host disease produced across minor histocompatibility barriers

Chronic graft vs host disease (GVHD) across minor histocompatibility barriers was produced in BALB/c mice by the injection of spleen cells from B10.D2 mice. Changes in the skin were analyzed in frozen sections using a panel of monoclonal antibodies detected by immunoperoxidase methods. Compared to control animals, a number of changes occurred in the skin of animals with chronic GVHD. In the epidermis, there were increased numbers of Thy-1-positive dendritic cells; keratinocytes expressed Thy-1 and Ia antigens. T lymphocytes appeared in both dermis and epidermis. In the early stages, cells with "helper" and "suppressor" phenotypes were present, while at later times "helper" cells remained in the epidermis and "suppressor" cells remained in the dermis. Cells bearing markers of macrophages were prominent in both dermis and epidermis after the second week. Of great interest was the appearance of spindle-shaped cells in the dermis which expressed Thy-1 and Ia. These cells resembled fibroblasts which may be activated to produce the excess collagen seen in the skin of chronic GVHD.

In vivo immunomodulation by monoclonal anti-L3T4. 1. Effects on humoral and cell-mediated immune response

The in vivo administration of monoclonal anti-L3T4 antibody has been shown to be an effective preventative and, in some cases, therapeutic treatment for several murine models of autoimmune disease. This report deals with the effect of such treatments on humoral and cell-mediated responses to T-dependent antigens. Both the primary and secondary IgG responses to tetanus toxoid were inhibited when anti-L3T4 was administered prior to immunization, but it was ineffective in modulating an ongoing IgG response. Cell-mediated immunity, as detected by in vitro antigen-specific proliferative responses, was inhibited only if anti-L3T4 was given prior to immunization. It was not effective if treatment was delayed until 48 hr prior to lymph node harvest even though greater than 90% of L3T4+ lymph node cells were depleted by this treatment. The refractory behavior of the lymph node cells to anti-L3T4 treatment was not exhibited by antigen-primed cells obtained from peripheral blood or spleen. The importance of these findings with regard to antibody therapy for chronic autoimmune disease is discussed.

A subset of T cell receptors associated with L3T4 molecules mediates C6VL leukemia cell binding of its cognate retrovirus

We show here that the interaction of a radiation leukemia virus-induced thymoma, C6VL, with its cognate retroviruses occurs in the vicinity of the T cell receptor (TCR). While an anti-clonotypic antibody completely inhibits this interaction, antibodies specific for another T cell receptor complex determinant, L3T4, only partially inhibit the cell-retrovirus interaction. Several antibodies to more abundant cell-surface determinants (T200, Ly15, H-2Db) do not inhibit this interaction. Under capping conditions, either of the antibodies to L3T4 or TCR epitopes modulate virus binding receptors from the surface of C6VL/1 cells. L3T4 and the TCR do not comodulate significantly on the surface of C6VL/1 cells. These experimental findings implicate the existence of rare TCR-L3T4 complexes on C6VL/1 cells, and the involvement of these complexes in the binding of C6VL/1 to its cognate retrovirus. In addition, the clonotypic anti-TCR antibody inhibits C6VL/1 cell proliferation at concentrations that block its binding to its produced retroviruses.

Differential requirement for accessory cells in polyclonal T-cell activation

Highly purified rat Ia-negative (OX-6-) and Ia-positive (OX-6+) T cells were employed to examine the requirement for accessory cells (AC) and/or soluble factors in the activation of resting T cells with Con A, PHA, sodium periodate, or antigen. A variety of cells were employed as AC, including Ia-positive and Ia-negative macrophages (M phi), gamma-irradiated (2000 rad) or non-irradiated OX-6+ T cells, and several Ia-negative adenovirus-transformed rat embryo fibroblast cell lines. Our results suggested that for the expression of IL-2 receptors (IL-2R) and proliferation of OX-6- T cells in response to Con A, PHA, or antigen, there was an obligatory requirement for the presence of AC which could not be overcome by the addition of IL-1 and/or IL-2. Activation of OX-6- T cells with antigen required the presence of Ia+ AC, while activation with mitogens could be initiated with Ia- AC. M phi were efficient in AC function in all responses tested, while the AC function of OX-6+ T cells (TAPC) proved discriminatory under different conditions. The optimal response to PHA required much higher concentrations of TAPC as AC than for the Con A response. TAPC failed to stimulate sodium periodate-treated T cells under any conditions tested. Furthermore, when TAPC were employed as AC, their antigen-presenting ability was radiosensitive, while their AC function for Con A and PHA was radioresistant. These results suggest that molecules involved in T cell-AC interactions may differ, depending on the source of AC and/or type of the proliferative stimulus provided to T cells. This data has been discussed in the context of T-cell activation.

The role of I-A/E molecules in B-lymphocyte activation. II. Mechanism of inhibition of the responses to lipopolysaccharide by anti-I-A/E antibodies

We have previously demonstrated that monoclonal anti-I-A/E antibodies inhibit B-cell responses to lipopolysaccharide (LPS). In the present report, the inhibitory effects were shown to be carried out directly on B cells, and to be totally independent of the LPS concentration used, thereby showing that antibodies do not mediate their effect through blocking of accessory cells or steric hindrance of LPS-receptors. Of the three different phases in B-cell activation/induction, proliferation, and maturation, induction was shown to be the most sensitive to inhibition by anti-I-A/E antibodies. Thus, kinetic studies showed that anti-I-A/E antibodies are only inhibitory for the first 16 h of LPS activation, after which B cells can no longer be inhibited by these antibodies. Class II MHC molecules appear, therefore, to be part of a membrane molecular complex which regulates delivery of activation signals to resting B cells. Since it was also shown that this time period corresponds approximately to the time required for B cells to express functional reactivity to growth factors, we suggest that anti-I-A/E antibodies act on resting B lymphocytes to inhibit mitogen-dependent induction of growth receptor expression.

Fine specificity and T-cell receptor beta-chain gene rearrangements of five H-2Db-specific cytotoxic T-cell clones

A panel of cytotoxic T lymphocyte clones that recognize H-2b target cells has been established. Six different clones were distinguished according to the following criteria. First, the fine specificity of the clones was determined by testing proliferation and cytotoxicity on target cells of recombinant mice. Clone 221 recognized H-2Kb, and five other clones recognized H-2Db. Clone 433 distinguished itself from the other five Db-specific clones by cross-reacting with an antigen on H-2k cells. Second, the presence of an idiotypic determinant as defined by the 3F9 clone-specific monoclonal antibodies was investigated in cytotoxicity inhibition experiments. One of the Db-specific clones, 653, was inhibited by these antibodies and was therefore clearly different from the other Db-specific clones. The third criterion involved the rearrangement pattern of the DNA coding for the beta chain of the T-cell receptor. Southern blot analysis showed that each clone had a unique pattern. Interestingly, clone 653, which expresses the same idiotypic determinant as clone 3F9, had deleted the C beta 1 gene cluster, whereas this gene is functionally expressed in clone 3F9.

Isolation of high-affinity memory B cells: phycoerythrin as a probe for antigen-binding cells

In multiparameter fluorescence-activated cell sorter studies presented here, we use the highly fluorescent protein phycoerythrin (PE) as an immunizing antigen and as a fluorescent probe to reveal and isolate antigen-binding memory B cells. We demonstrate directly that memory B cells in spleens from PE-primed mice stain brightly with PE and produce strong IgG1 anti-PE responses when sorted and cultured with L3T4+ helper T cells. That is, as few as 500 sorted PE-binding cells per culture well are sufficient to produce high-level anti-PE responses, presenting antigen in a form that induces helper T cells. Three-color immunofluorescence studies reveal that cells staining brightly with PE reside primarily in a population of B220+(IgM,IgD)- cells and comprise 0.02-0.05% of the spleen cells. Complementary studies with 2,4-dinitrophenyl memory B cells show that whereas this B220+-(IgM,IgD)- population (which comprises only 1-2% of the spleen cells) gives high-affinity anti-dinitrophenyl responses, the predominant B220+(IgM,IgD)+ population yields only low-affinity antibody. Finally, we find that although both populations have similar Ia levels, cells in the high-affinity fraction have greatly reduced levels of surface immunoglobulin.

Accessory molecules and T cell activation. II. Antibody binding to L3T4a inhibits Ia-independent mouse T cell proliferation

Monoclonal antibody (mAb) blocking assays using L3T4- and lymphocyte function-associated antigen-1 (LFA-1)-specific reagents were used as an approach to investigate the involvement of these accessory molecules in various T cell activation pathways. As previously reported, rat mAb to L3T4a and LFA-1A functional epitopes efficiently blocked antigen-driven T helper cell proliferation. In contrast, antigen- and Ia-independent T cell triggering induced by appropriate mAb to the Thy-1 or the T cell receptor molecules were found to be inhibitable by L3T4a- but not LFA-1A-specific mAb, although the extent of inhibition varied, depending on the cell type and the activating signal examined. These results provide further evidence that the inhibiting effects of L3T4-specific mAb on T cell responses may be due, in addition to an impairment of L3T4-class II major histocompatibility complex molecular interaction, to a down regulatory signal possibly transmitted by the L3T4 molecule itself.

Cutaneous leishmaniasis. The defect in T cell influx in BALB/c mice

Local cellular responses to cutaneous infection with Leishmania mexicana amazonensis were examined in susceptible (BALB/c) and resistant (C57BL/6) mouse strains by immunocytochemical and electron microscopic studies. Infection during the first 8 wk in both animal strains was characterized by progressively enlarging lesions, epidermal thickening and ulceration, and accumulation of eosinophils and Ia+ infected macrophages. Healing of C57BL/6 mouse lesions began after 12 wk of infection and was associated with local influx of both Th (L3T4+) and T cytotoxic/suppressor (Lyt-2+) cells into the dermis, and Ia antigen expression on epidermal keratinocytes. T lymphocyte infiltration was marked and intracellular parasites were scarce by 21 wk of C57BL/6 infection. Similarly, granulomas in C57BL/6 livers contained L3T4+ and Lyt-2+ T lymphocytes and no visible intracellular parasites by 21 wk of infection. In contrast, BALB/c mouse lesions continued to enlarge and never healed. Throughout the entire course of infection, T lymphocyte influx into the heavily infected dermis was minimal. Keratinocyte Ia expression was absent in BALB/c lesions. BALB/c livers were heavily infected by 18 wk of cutaneous infection, with few demonstrable T lymphocytes. A systemic absence of T cells could not be demonstrated in BALB/c mice. Both L3T4+ and Lyt-2+ T cells were found in the peripheral blood in normal numbers in both mouse strains. Our results support the role of T cells as important local effector cells in the healing response of murine cutaneous leishmaniasis. We suggest that local T lymphocyte infiltration may provide lymphokines, particularly IFN-gamma, that can activate infected macrophages to destroy the intracellular parasites. Alternatively, T cells may play a cytotoxic role, killing infected macrophages and allowing local humoral factors to destroy released extracellular parasites.

Specific lysis of Listeria monocytogenes-infected macrophages by class II-restricted L3T4+ T cells

Mice were infected with the intracellular bacterium, Listeria monocytogenes, and T cell clones from spleens, lymph nodes and peritoneal exudates were established. The capacity of L3T4+, Lyt2- T-cell clones to specifically lyse L. monocytogenes-infected macrophages was analyzed. As a source of target cells, bone marrow macrophages (BMM phi) after 9 days of culture in hydrophobic teflon bags were used. These BMM phi were totally Ia-; however, significant Ia-expression could be induced by interferon-gamma (IFN-gamma). IFN-gamma-stimulated BMM phi, after priming with live or killed L. monocytogenes organisms were effectively lysed by the vast majority of L3T4+ T cell clones. In the absence of either IFN-gamma stimulation or antigen priming, no lysis occurred. Cytolysis was demonstrable in a conventional 4-h 51Cr-release assay and in an 18-h neutral red uptake assay and was antigen specific and class II restricted. Native T cells from L. monocytogenes-infected mice failed to lyse stimulated, L. monocytogenes-primed BMM phi and gained their cytolytic activity after antigenic restimulation in vitro. These data demonstrate that L. monocytogenes-specific L3T4+ T cells could lyse M phi presenting listerial antigens provided that Ia antigen expression had been induced. L3T4+ T cell clones produced IFN-phi after restimulation with antigen plus accessory cells in vitro and IFN-gamma secretion could be increased by costimulation with recombinant IL 2. These T cell clones conferred significant protection upon recipient mice which was more pronounced in the liver. The possible relevance of lysis by L3T4+ T cells of infected M phi to protection against and pathogenesis of intracellular bacterial infections is discussed.

Identification of interleukin 2-producing T helper cells within murine Lyt-2+ T lymphocytes: frequency, specificity and clonal segregation from Lyt-2+ precursors of cytotoxic T lymphocytes

The prime aim of this study was to assess whether the autonomous primary mixed lymphocyte culture response of Lyt-2+ T cells towards class I major histocompatibility complex (MHC) antigens reflects in terms of interleukin 2 (IL2) production and cytotoxicity the activation of multifunctional Lyt-2+ T cells, or the activation of functionally distinct T cell subsets. The results demonstrate that highly purified Lyt-2+ T cells proliferate in response to class I MHC antigens, as opposed to L3T4+ T cells which react towards class II MHC antigens. In both responder cell types proliferative responses are associated with IL2 secretion, while only Lyt-2+ T cells develop measurable cytotoxic effector cells. The precursor frequency of IL2-producing helper cells in MHC class I-reactive Lyt-2+ T cells equals that in MHC class II-reactive L3T4+ T cells (f = 1/500-1/1000). In clonal segregation analysis greater than 90% of Lyt-2+ colonies secreting IL2 do not develop cytotoxic activity, while greater than 90% of Lyt-2+ cytotoxic T cells fail to produce detectable IL2. A minority of less than 10% of Lyt-2+ T cells appears to be bifunctional. As such the results point out the existence of functionally committed T cells within class I MHC-reactive Lyt-2+ T cells able to produce either IL2 or to develop into cytotoxic effector cells.

Differential expression of asialo GM1 on alloreactive cytotoxic T lymphocytes and lymphokine-activated killer cells

The present study was undertaken to examine the differential expression of asialo GM1 (AsGM1) on the responding cells and effectors of alloreactive cytotoxic T lymphocytes (CTL) and lymphokine-induced activated killers (LAK). It was found that AsGM1 was expressed on the 3-day-cultured LAK effectors. Its expression gradually disappeared to the extent that AsGM1 became undetectable after 5 to 6 days of culturing. In contrast, AsGM1 was detected on 3-day CTL generated in mixed-lymphocyte cultures (bulk cultures); however, the levels of AsGM1 expression remained the same for at least 7 days. When examining the expression of AsGM1 on the responding cells, the reciprocal results were obtained. AsGM1 was expressed the LAK responders, but we were unable to demonstrate AsGM1 on CTL responders. Depletion of AsGM1+ cells from the responding population reduced subsequent CTL responses; however, CTL responses could be restored by adding conditioned media containing both interleukin 2 (IL-2) and other helper-T-cell factors and could not be restored by purified IL-2 alone adding at comparable doses. Reconstituting the AsGM1-depleted responders with Lyt-2-depleted splenocytes also restored the CTL response. Furthermore, depletion of AsGM1 cells from the responding population did not reduce the precursor frequency of allo-CTL, whereas the precursor frequency of LAK cells was reduced 42-fold. These findings show that the reduction of CTL responses after depletion of AsGM1+ cells was not due to the removal of precursors; instead, the defect appeared to be in the helper population. We further found that the helper defect was not due to impaired IL-2 production, because the endogenous production of IL-2 AsGM1-depleted responders was not reduced. Therefore, AsGM1+ cells may play a role in the helper pathway other than IL-2 production.

The MRC OX-44 antigen marks a functionally relevant subset among rat thymocytes

A monoclonal antibody called MRC OX-44 is described that labels all myeloid cells and peripheral lymphoid cells but only 12% of thymocytes. The OX-44+ thymic cells include most if not all cells found in the medulla but only a small fraction of the cortical cells. Together with CD4 and CD8 antigens, seven subsets of thymic cell were defined and it was notable that most CD4- CD8- cells were OX-44+ whereas almost all CD4+ CD8+ cells were OX-44-. In functional tests, the OX-44+ cells accounted for all proliferation by thymocytes when stimulated by allogeneic spleen cells or concanavalin A plus growth factors and OX-44- cells were completely negative in these assays. Also, in tests for thymopoiesis after intra-thymic injection of cells, all activity was OX-44+. It seems possible that the OX-44+ set may include all functionally relevant cells in the rat thymus.

Melphalan-induced appearance of potent antitumor immune reactivity in tumor bearer lymphocytes co-expressing the Lyt 2 and the L3T4 antigens

We have previously shown that Sephadex G-10-adherent spleen cells from mice bearing a large MOPC-315 tumor can suppress the in vitro generation of a primary anti-MOPC-315 cytotoxic response. Here we show that following low dose melphalan (L-phenylalanine mustard; L-PAM) therapy of such tumor bearing mice their Sephadex G-10-adherent spleen cells no longer suppressed but actually brought about the generation of enhanced antitumor cytotoxicity when added to the immunization culture of normal spleen cells and MOPC-315 tumor cells. This immunopotentiating activity of the Sephadex G-10-adherent spleen cells from L-PAM treated MOPC-315 tumor bearers was attributed to T-cells which co-express the Lyt 2 and the L3T4 antigens based on results of experiments employing negative selection. Specifically, depletion of Lyt 2+ cells or of L3T4+ cells abolished the ability of the Sephadex G-10-adherent splenic cell population from L-PAM treated MOPC-315 tumor bearers to bring about the generation of enhanced antitumor cytotoxicity when added to the immunization culture of normal spleen cells. Moreover, the immunopotentiating activity was not restored when a population of Sephadex G-10-adherent spleen cells depleted of Lyt 2+ cells was admixed with a population of Sephadex G-10-adherent spleen cells depleted of L3T4+ cells. In light of the unusual phenotype of the immunopotentiating cells in the spleens of L-PAM treated MOPC-315 tumor bearing mice (i.e. Lyt 2+ L3T4+), and since the vast majority of thymocytes in normal adult BALB/c mice co-express the Lyt 2 and the L3T4 antigens, we evaluated the effect of low dose L-PAM therapy on the antitumor immune reactivity of thymocytes from MOPC-315 tumor bearing mice. A low dose of L-PAM was found to render thymocytes from MOPC-315 tumor bearers, but not from normal mice, capable of bringing about the generation of enhanced lytic activity when added to the immunization culture of normal spleen cells and MOPC-315 tumor cells. At the same time, the thymocytes from L-PAM treated MOPC-315 tumor bearers were unable to develop an antitumor cytotoxic response of their own when immunized in vitro in the absence of normal spleen cells. The possibility that the Lyt 2+ L3T4+ immunopotentiating cells in the spleens of L-PAM treated MOPC-315 tumor bearers represent immature cells that have been induced by the chemotherapy to migrate from the thymus into the spleen is discussed.

Immunopharmacological studies of PTT.119, a new synthetic bis-(2-chloroethyl)amino-L-phenylalanine derivative

The new synthetic tripeptide p-F-Phe-m-bis-(2-chloro-ethyl)amino-Phe-Met-etoxy HCl, PTT.119, was studied for its effects on the host immune system. Doses of PTT.119 ranging from 3 to 18 mg/kg were administered i.p. to recipient mice which, at different times after drug treatment, were tested for allograft response, competence in producing lymphocytes active in lethal graft-versus-host disease, delayed-type hypersensitivity, mitogen responsiveness, humoral antibody production and natural resistance against microbial infections. At therapeutically active dosages, PTT.119 appeared to selectively inhibit functions mediated by B lymphocytes, leaving the majority of those involving T-cell subsets largely unaffected, even at the highest doses employed. Moreover, drug treatment had also a limited impact on the in vivo resistance of mice to microbial infection, which was only affected by a drug injection of 18 mg/kg, a dose well within the confidence limits of the mean lethal dose of the drug.