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

Epitopes associated with the MHC restriction site of T cells. II. Somatic generation of Iat epitopes on T cells in radiation bone marrow chimeras

We described in this paper systematic alterations in the expression of unique I region controlled epitopes on helper T cells (Th) in chimeras according to the changes in their H-2 restriction specificity. Taking advantage of the reactivity of monoclonal antibodies (anti-Iat) putatively specific for the epitopes indirectly controlled by I region and expressed in association with the Iak restriction site of Th, we examined the alterations of these epitopes on Th cells from various bone marrow chimeras. Iatk epitopes were physiologically expressed on Iak-restricted but not on Iab-restricted Th cells in (H-2k X H-2b)F1 mice. In the chimeric condition, the H-2k-restricted Th of B6----F1 chimera acquired the expression of Iatk even though B6 Th is unable to express Iatk when developed under the physiologic condition. Iatk are also found on Th of fully allogeneic chimera of B6----C3H, whereas Th cells of C3H----B6 completely lost the Iatk expression. These results indicate that Iat epitopes originally defined as unique I region-controlled determinants selectively expressed on T cells are not encoded by the I region genes but are associated with the T cell receptor that sees the self Ia. The epitopes undergo the adaptive alterations according to the acquisition of a new MHC restriction. This is the first example to demonstrate the epitope associated with T cell receptor which undergo the systematic adaptive differentiation.

LFA-1 and other accessory molecules functioning in adhesions of T and B lymphocytes

Adhesions of lymphocytes, among themselves or with other cell types, are necessary for most steps in immune responses including both induction and effector phases. Among adhesions of T cells involving specific immunological recognition, CTL-target adhesions have been the most studied. Although CTL-mediated killing is highly specific (specific/nonspecific lytic activity 50-fold), CTL-target adhesion (conjugation) is less so. In the mouse, specificity of conjugation has typically been four to eightfold. Two recent studies with cloned human CTL found much less specificity of conjugation, from one-fold (no specificity) to 1.5-fold. Thus, with cloned human CTL, adhesion may occur promiscuously with any potential target; recognition following adhesion is necessary for lethal hit delivery. The fact that antibodies to the antigen receptor (Ti or CD3) inhibit killing without inhibiting CTL-target conjugation supports this view. The ability of lymphocytes to form nonspecific adhesions, plus the dependence of even the specific mouse adhesions on temperature, metabolic energy, magnesium, and an intact cytoskeleton suggest that the bulk of the strength of T lymphocyte adhesions are not simply the sum of the bonds between antigen receptors (Ti) and antigen. Lymphocytes evidently possess separate "adhesion strengthening" mechanisms. The similarities in the properties of CTL-target adhesions and antigen-independent homotypic B lymphocyte adhesions (Table 2) suggest that at least some of these mechanisms are widely used among cells of hematopoietic origin. MoAbs to most lymphocyte surface molecules, when bound to the living lymphocyte membrane, have no evident functional effects on lymphocyte function. However, a minority can either activate or inhibit lymphocyte functions. Such antibodies identify "leukocyte (or lymphocyte) function-associated antigens," or LFAs (not all of which happen to have "LFA" in their names, Table 1). Most of the inhibitory antibodies inhibit lymphocyte adhesions, and this appears to account for their inhibitory effects on functions such as killing or proliferation. The fact that the binding of antibodies to a particular membrane glycoprotein inhibits adhesion does not guarantee that the glycoprotein in question is a direct participant in adhesion (one of the "glue" molecules). However, there is scanty evidence in support of indirect "negative signals" that may be induced by such antibodies, and direct participation of most LFAs in adhesion seems likely.(ABSTRACT TRUNCATED AT 400 WORDS)

B cell stimulatory factor 1 (interleukin 4) is a potent costimulant for normal resting T lymphocytes

Resting T cells proliferate in response to B cell stimulatory factor 1 (BSF-1; interleukin 4) plus phorbol myristate acetate (PMA). This response is obtained with highly purified T cells and is density independent, suggesting that accessory cells are not required. Both L3T4+ and Lyt-2+ T cells respond to BSF-1 plus PMA. Although BSF-1 alone does not cause T cell proliferation, it maintains the viability of small, dense T cells, indicating that it acts on resting T cells. Furthermore, BSF-1 is required early in the proliferative response of resting T cells to BSF-1 plus PMA, further supporting the concept that it acts on G0 or early G1 cells. However, BSF-1 is also needed late in the first round of division of T cells stimulated with BSF-1 plus PMA. Removing BSF-1 at 24 h of stimulation prevents entry into S phase. These results indicate that BSF-1 is involved in both the induction of competence and in the progression phases of T cell division.

Anti-L3T4 antibody treatment suppresses hepatic granuloma formation and abrogates antigen-induced interleukin-2 production in Schistosoma mansoni infection

In murine schistosomiasis mansoni, granulomatous inflammation is an immune response that involves egg antigen presentation to T cells in the context of class II major histocompatibility complex determinants and subsequent inflammatory lymphokine production by delayed-hypersensitivity (TDH) lymphocytes. In the present study, monoclonal antibodies directed against L3T4, I-A, and Lyt-2 molecules were injected intraperitoneally into S. mansoni-infected mice to study the role of these membrane antigens in the process of granuloma formation. A dramatic suppression of the hepatic granuloma size and antigen-induced interleukin-2 (IL-2) production by spleen cells was seen in mice that received anti-L3T4 monoclonal antibody treatment. The total number of cells, especially the L3T4+ T cells, was greatly diminished in the spleens. Furthermore, histopathological study of the granulomas in stained liver sections demonstrated the paucity of eosinophils and macrophages, absence of epithelioid cells and multinucleated giant cells, and minimal collagen deposition within the lesions. Damaged hepatocytes were also seen surrounding these ill-formed granulomas. In contrast, anti-I-A monoclonal antibody treatment partially suppressed IL-2 production, although granuloma size and cellular composition remained the same. Mice that received anti-Lyt-2 monoclonal antibody did not show any changes in either IL-2 production or hepatic granulomatous inflammation. The data presented in this paper indicate a crucial role for L3T4 molecules present on a subset of class II major histocompatibility complex-restricted TDH cells in IL-2 production and the generation of the granulomatous response.

Simultaneous expression of multiple immune complex receptors on murine thymocytes and spleen cells

Mixed rosette studies were performed to evaluate the coexpression of IgG Fc. IgM Fc, and complement receptors (C3R) by thymocytes obtained from mice 7 days after cortisone injection and by spleen cells. Indicator cells coated with IgM, IgG, or C3 independently were mixed and could be distinguished by morphology or by a fluorescein label. In double-marker studies, 36% of spleen cells formed rosettes with IgG- and/or IgM-sensitized red blood cells. Among this population there was a 24% overlap of cells binding IgM and IgG complexes simultaneously. Of the spleen cells, 78% bound IgM- and/or C3-sensitized cells. Of the spleen cells forming rosettes with IgM and C3 indicator cells, 15% coexpressed these receptors. With IgG and C3 indicator cells, 58% of spleen cells bound to one or both kinds of complexes with an 18% overlap. Of cortisone-resistant thymocytes, 14% formed rosettes with IgM- and/or IgG-sensitized red blood cells; within this population there was an overlap of 21%. With IgM- or C3-sensitized cells, 19% of cortisone-resistant thymocytes bound to one or both, among which there was a coexpression of 21%. With IgG- or C3-sensitized cells, there was a 14% overlap of rosette-forming cells binding both. In triple-marker studies 79% of spleen cells formed rosettes with C3-, IgG-, and/or IgM-sensitized indicator cells, out of which 11% coexpressed IgM and IgG FcR, 20% coexpressed IgG and C3R, and 10% coexpressed IgM FcR and C3R. Of rosette-forming cells, 13% coexpressed all three receptors. With cortisone-resistant thymocytes, 19% bound one or more kinds of immune complexes. Among these, 9% coexpressed IgG FcR and C3R, 14% coexpressed IgM FcR and C3R, and 14% bound IgG and IgM complexes. We could not detect the simultaneous expression of all three receptors on cortisone-resistant thymocytes. Using Isopaque-Ficoll fractionation of cells binding C3-sensitized cells, cortisone-resistant thymocytes were enriched and depleted of C3-receptor-bearing cells and their Lyt phenotypes were determined by immunofluorescence microscopy. The C3-receptor-enriched population contained 56% C3R+ cells which were 79% Lyt-1 positive and 100% Lyt-2 positive. The C3R-depleted population contained 1.3% C3R+ cells with 10% Lyt-1 positive and 22% Lyt-2 positive among the total. Surface phenotypic expression of normal and cortisone-resistant thymocytes was also evaluated by direct and indirect fluorescence by fluorescence-activated cell sorter (FACS).(ABSTRACT TRUNCATED AT 400 WORDS)

Structural characterization of the TAP molecule: a phosphatidylinositol-linked glycoprotein distinct from the T cell receptor/T3 complex and Thy-1

Here we characterize the T-cell-activating protein (TAP), an Ly-6 gene product involved in T cell activation, as a glycoprotein with a molecular weight of 10-12 kd under nonreducing conditions and 15-18 kd under reducing ones. Two of the three bands that are precipitated from metabolically labeled cells are expressed on the cell surface and can be recovered from the supernatants of cells treated with a phosphatidylinositol-specific phospholipase C. Thus TAP appears to be attached to the cell membrane via this lipid. Precisely the same anchorage is observed for the activating Thy-1 molecule, and is therefore of particular interest as a potentially novel linkage involved in membrane signal transduction.

Increased T epsilon cells in BALB/c mice with an IgE-secreting hybridoma

Since it has been proposed that T cells with receptors for the Fc portion of IgE (T epsilon) in rats, mice and humans are IgE-specific regulatory cells, it was investigated whether mice with an IgE-secreting hybridoma might be a source of large numbers of T epsilon cells. BALB/c mice with ascitic tumors of the IgE hybridoma B53 (epsilon, kappa, anti-DNP) developed high serum concns of monoclonal IgE which was followed by the appearance of large numbers of Lyt1-2+ L3T4- T epsilon cells. In contrast, mice bearing a non-IgE producing variant of B53 failed to develop T epsilon cells. Mice infused with cell-free ascites fluid (containing high levels of monoclonal IgE) from the IgE-secreting B53 hybridoma developed high serum IgE levels and also developed high numbers of T epsilon cells. Mice infused with cell-free ascites obtained from the non-IgE-secreting variant ENP-1 (containing very low amounts of IgE) did not develop either high serum IgE levels or T epsilon cells. These findings suggest that high serum IgE concns induce large numbers of T cells that express phenotypic markers of suppressor cells and have surface IgE-Fc receptors. These studies extend to IgE the principle that hybridomas and plasmacytomas induce large numbers of immunoregulatory T cells that express Fc receptors specific for the heavy chain class of the secreted monoclonal immunoglobulin. Since T epsilon cells are normally present only in small numbers, their marked increase in mice with IgE-secreting hybridomas identifies a ready source of large numbers of T epsilon cells that can be used to investigate their regulatory properties.

Highly malignant tumor variants retain tumor-specific antigens recognized by T helper cells

We have studied the components of a complex of tumor-specific antigens to determine if all of the components of the complex were lost during progression from a rather benign regressor tumor to a highly malignant (HM) cancer. We find that the HM tumor cells have lost antigens recognized by CTL but retained antigens recognized by Th cells. Immunization with variants expressing Th-defined antigens induced tumor-specific immunity to challenge with a parental variant that expressed a CTL-recognized target antigen, but did not induce immunity to challenge with the variant that expressed the Th-defined antigen alone. Together, these findings suggested that Th cells fail to exert direct selective pressure upon the tumor, resulting in retention of "lineage-specific," Th-recognized antigens by highly immunoselected variants. Possible advantage could be taken of this fact for the development of specific immunotherapy.

Expression of L3T4 molecules on Lyt-2+, class II-restricted antigen-specific T suppressor lymphocytes

Three bovine serum albumin-specific Lyt-2+ T suppressor (Ts) cell clones from CBA/J mice have been analyzed with regard to expression of L3T4 molecules. All three Ts-cell clones can be stained with monoclonal antibodies (mAb) to L3T4. Tested for the two clones restricted to recognition of Ek determinants, antigen-specific proliferation on antigen-presenting cells, but not the proliferation induced by conditioned medium can be inhibited by L3T4-specific mAb. In a similar way, Ts-cell cytolytic effector functions can be blocked by L3T4-specific mAb. Thus L3T4 structures seem to play a role in Ts-cell functions. Furthermore, the data support the view that L3T4 expression can be a property of class II-restricted T cells irrespective of their Lyt phenotype.

Stable expression of Lyt-2 homodimers on L3T4+ T cell clones

The murine T lymphocyte antigen Lyt-2 is considered to act as an accessory molecule to the class I-restricted T cell receptor during antigen recognition. We have previously described two unusual Lyt-2+L3T4+ class II-restricted T cell clones whose activation by antigen is inhibited by antibodies to L3T4 but not to Lyt-2 (B. Fazekas de St. Groth et al., Proc. Natl. Acad. Sci. USA 1986. 83: 2594). The Lyt-2 immunoprecipitated from one of these clones was indistinguishable from the molecule found on splenic T cells, as analyzed under reducing conditions on polyacrylamide gels, in two-dimensional charge/size separations and in peptide mapping. The molecule from the second clone showed slightly more extensive glycosylation but was within the range described for functional Lyt-2 on cytotoxic T cell lines. Lyt-2 mRNA from both clones showed no abnormalities on Northern analysis. Lyt-2 is normally expressed on thymocytes and peripheral T cells as a heterodimer disulfide bonded to the Lyt-3 glycopeptide, yet Lyt-3 could not be detected on the cell membranes of our clones; Lyt-2 existed as stable homodimers without Lyt-3. Thus Lyt-3 is not required structurally for the spontaneous expression of Lyt-2 on lymphoid cells.

Isolation and sequence of L3T4 complementary DNA clones: expression in T cells and brain

T lymphocytes express on their surface not only a specific receptor for antigen and major histocompatibility complex proteins, but also a number of additional glycoproteins that are thought to play accessory roles in the processes of recognition and signal transduction. L3T4 is one such T-cell surface protein that is expressed on most mouse thymocytes and on mature mouse T cells that recognize class II (Ia) major histocompatibility complex proteins. Such cells are predominantly of the helper/inducer phenotype. In this study, complementary DNA clones encoding L3T4 were isolated and sequenced. The predicted protein sequence shows that L3T4 is a member of the immunoglobulin gene superfamily. It is encoded by a single gene that does not require rearrangement prior to expression. Although the protein has not previously been demonstrated on nonhematopoietic cells, two messenger RNA species specific for L3T4 are found in brain. The minor species comigrates with the L3T4 transcript in T cells, whereas the major species is 1 kilobase smaller.

Transcripts of functionally rearranged gamma genes in primary T cells of adult immunocompetent mice

The T-cell specific, rearranging gamma-chain genes bear striking resemblance to T-cell receptor and immunoglobulin genes, but the role of gamma remains unknown. A central problem is to understand the conditions under which gamma RNA is expressed in cells. The transcription of gamma is abundant in T cells of fetal thymi, but is negligible in peripheral T cells of adults, suggesting that gamma is involved in development of the T-cell repertoire. However, gamma RNA was originally cloned from established lines of cytotoxic T cells (CTLs) derived from adult mice and this expression has been ascribed to non-physiological cell growth. Possibly consistent with this, most of the gamma RNA derives from genes rearranged abortively at the V gamma-J gamma junction of immunoglobulin genes, where V is the variable segment and J the joint segment. Here, we report the detailed analysis of gamma transcription in T cells of adult mice, and find that transcription may occur in T cells with a broad range of surface phenotypes; that it is predominantly of a single V gamma-C gamma unit (where C is the constant region); and that in cells freshly explanted from animals it can be of productively rearranged genes.

T cell receptor expression and receptor-mediated induction of clonal growth in the developing mouse thymus. High surface beta-chain density is a requirement for functional maturity

The ontogeny of T cell antigen receptor expression and function in the mouse thymus has been studied using a monoclonal antibody, F23.1, which recognizes a determinant on the beta chain of the receptor, and stains 25% of mature T cells and around 7-15% of adult thymocytes from most mouse strains. The same monoclonal antibody selectively activates Lyt-2+ peripheral T cells. Receptors are detectable by staining and fluorescence-activated cell sorter analysis from fetal day 17, and thereafter the overall frequency increases steadily towards adult levels. However, late fetal thymocytes express all of their antigen receptor beta chain at a very low level, visible by staining as a "shoulder" on the peak of negative cells. Thymocytes with high-density surface beta chain, visible by staining as a distinct peak, appear only after birth and are a prominent feature at neonatal day 4. In the late fetus, expression of beta chain can be detected on thymocytes with the "mature" L3T4-, Lyt-2+ phenotype. Despite this, F23.1-responsive precursors are not found in the fetal thymus, and appear in two waves, the first during day 1 of postnatal life and the second between days 3 and 4. These data suggest that high-density surface expression of T cell receptor beta chain occurs in parallel with functional maturation.

Expression of T-cell-activating protein in peripheral lymphocyte subsets

T-cell-activating protein (TAP) is an allelic 12-kDa membrane protein that participates in T-cell activation. Soluble anti-TAP monoclonal antibodies can trigger antigen-specific, major histocompatibility complex-restricted T-cell hybridomas to produce interleukin 2 and are mitogenic for normal T cells and thymocytes. TAP is expressed on 10% of thymocytes, which are mainly cortisone-resistant and mature. In the periphery, TAP is expressed on 70% of resting T cells but not on resting B cells. In this report, we analyze in detail the nature of TAP expression on peripheral lymphocyte subsets by immunofluorescence techniques. We show that all inducer (L3T4+) T cells are TAP+. In contrast, only 50% of Lyt-2+ T cells express detectable TAP. Functional studies demonstrated that at least part of the heterogeneity of TAP expression is present in the Lyt-2+ cytolytic T-cell (CTL) subset. Unstimulated CTL precursors are TAP- but are induced to express TAP in the effector state. Furthermore, this reflects actual synthesis of TAP, as TAP is detectable on activated Lyt-2+ CTLs passaged in vitro under conditions where passive acquisition can be ruled out. To extend this observation, we have studied the expression of TAP on activated T and B cells. Upon activation, all T and B cells became TAP+. Furthermore, the TAP molecules on B and T cells are indistinguishable by NaDodSO4/polyacrylamide gel electrophoresis. This suggests that TAP expression defines further heterogeneity of lymphocytes, with activation being one parameter influencing its expression.

Isolation of cell lines possessing functional and serological properties resembling those of thymocyte precursors

Thymocytes develop from a committed haematopoietic progenitor, referred to as a prothymocyte. They are uniquely capable of migrating to and restoring the thymus of a lethally irradiated host, a property which has been exploited as a specific assay for these cells. Like other committed haematopoietic progenitors, prothymocytes are found only in small numbers in even the richest sources (0.05-1.0% of the nucleated cells in bone marrow). Purification has proved difficult both in terms of finding a suitable starting material and in the degree of enrichment achieved. We now report the isolation of cloned lines of cells with some of the serological and functional properties of prothymocytes. One of these lines has been in continuous culture for almost 2 years. When injected into irradiated recipients, cells from this line migrate to the thymus and there develop into cells which resemble normal cortical thymocytes.

Monoclonal antibodies to promote marrow engraftment and tissue graft tolerance

Allogeneic reactions are the major limitation to organ transplantation. These are manifested as rejection of the grafted tissue, and also, in the case of bone marrow transplantation (BMT), graft-versus-host disease (GVHD). Recent methods of avoiding GVHD, by depleting T cells from donor marrow, have led to an increased incidence of marrow graft rejection. Current recipient conditioning protocols involving drugs or irradiation cannot safely be increased, so alternatives must be found. Monoclonal antibodies can be used to control immune responses in vivo, and would be useful in this context if we could define and deplete the cells responsible for marrow rejection. We show here that elimination of residual L3T4+ and Lyt-2+ cells from mice receiving fully mismatched bone marrow abrogates rejection and promotes tolerance to donor-type skin grafts, even in sub-lethally irradiated recipients.

Role of Ly-6 in lymphocyte activation. II. Induction of T cell activation by monoclonal anti-Ly-6 antibodies

The Ly-6 locus controls the expression and/or encodes for alloantigenic specificities found primarily on subpopulations of murine T and B lymphocytes. We have recently identified and characterized a new rat mAb, D7, that recognizes a nonpolymorphic Ly-6 specificity. After crosslinking by anti-Ig reagents or by Fc receptor-bearing accessory cells, mAb D7 could induce IL-2 production from T cell hybridomas, and in the presence of PMA could trigger a vigorous proliferative response in resting peripheral T cells. The addition of mAb D7 to cultures of antigen- and alloantigen-, but not mitogen-stimulated T cells resulted in a marked augmentation of the proliferative response. A number of other well-characterized mAbs to Ly-6 locus products could also stimulate a T cell proliferative response after crosslinking by anti-Ig and in the presence of PMA. These results strongly suggest that Ly-6 molecules may play a critical role in the T cell activation cascade, either as receptors for an unidentified soluble or cell-associated ligand or as transducing molecules that modulate signals initiated by antigen stimulation of the T3-Ti complex.

Detection of rearranged T cell receptor beta-chain gene and induction of cytolytic function in interleukin 2-responsive day 14-15 murine fetal thymocytes

A subpopulation of interleukin 2 (IL 2) receptor-positive day 14-15 murine fetal thymocytes can be induced by recombinant IL 2 to proliferate over prolonged time periods in dissociated cell cultures. The proliferating day 14-15 fetal thymocytes exhibit no cytolytic effector function, nor do they rearrange T cell receptor beta chain genes. This contrasts with thymic organ cultures in which day 14-15 thymocytes do rearrange beta chain genes and give rise to immunocompetent cells. However, such events can also take place in dissociated cell cultures, provided the IL 2-responsive thymocytes are cultured on syngeneic feeder cells in the presence of IL 2 and the mitogen concanavalin A. Under such conditions rearrangement of the beta chain gene complex becomes detectable and cytolytic effector cells are generated. The frequency of inducible cytolytic precursor cells in day 14-15 thymocytes is 1/7000. These data either imply that immunocompetent cells are already present in the day 14-15 fetal thymus, or differentiation from precursors to immunocompetent cells must occur in dissociated cell cultures.

Inducer T-cell-mediated killing of antigen-presenting cells

L3T4+ inducer/helper T-cell clones, once activated by antigen-presenting cells (APC) expressing the appropriate Ia allele and antigen, autonomously kill their target APC. All 13 L3T4+ inducer T-cell clones tested demonstrated this cytolytic activity. In addition, 11 different target cells representing the three major APC types, namely, macrophages, B cells, and dendritic cells, were all sensitive to this cytolytic activity. Moreover, normal macrophages which were treated with interferon-gamma to increase Ia expression were also killed. These observations convincingly demonstrate that the cytolytic activity of L3T4+ inducer T-cell clones is a general phenomenon. In contrast to other reports, lysis of target APC could not be detected following 4-6 hr of incubation. Marginal lysis was observed after 9 hr and a 20-hr incubation period was required to achieve maximal killing. The kinetics of killing paralleled other parameters of T-cell activation such as IL-2 release and cell proliferation. Activation of T cells for cytolysis of APC requires the interaction of T-cell receptors with Ia and antigen. Monoclonal antibody to Ia, L3T4 and the T-cell receptor inhibited the cytolysis of APC. The ability to mediate nonspecific bystander killing was variable depending on both the T-cell clone and the target. The implications of these findings to immune regulation and autoimmunity are discussed.

Regulation of the cytotoxic activity of alloreactive cytotoxic T lymphocytes by helper cells and lymphokines

The cytotoxic activity of alloreactive cytotoxic T lymphocytes (CTL) was maintained and augmented by transferring cells from a 5-day mixed lymphocyte culture MLC into a host culture (HC) containing indomethacin, freshly explanted normal spleen cells, and peritoneal cells which were syngeneic to the MLC cells. The MLC cells used in the transfer experiments were generated by culturing untreated H-2b splenic responders with irradiated H-2d stimulators, or were generated by culturing Lyt-2-depleted H-2b splenic responders with irradiated H-2d stimulators. The allo-CTL were found to be derived from the donor MLC (first culture) when unfractionated MLC cells were transferred into a host (second) culture and incubated for 5 days. In contrast, the allo-CTL were derived from host culture cells when Lyt-2-depleted MLC cells were transferred and the combined cultures incubated for 5 days. In the former case, the augmentation of MLC-derived cytotoxicity did not result from nonspecific expansion of all donor T cells; instead it was mediated by lymphokine(s), distinct from IL-2, produced by helper T cells generated in host culture, which appeared to selectively expand the antigen-specific CTL or to increase the cytotoxic activity of these CTL. The helper T cells were Thy-1+, L3T4+, and Lyt-2-. These findings indicate that antigen-nonspecific help was provided by helper cells or helper factors (lymphokines) generated in the host culture, which maintained and augmented the cytotoxic activity of the fully generated allo-CTL. This helper effect was also seen in the induction of primary allo-CTL responses which could be generated with fewer stimulating cells and with a stronger cytotoxic response at different R/S ratios tested. The generation of allo-CTL in second culture following transfer of Lyt-2-depleted MLC cells to host cultures appears to have involved antigen carryover from the MLC; however, antigen carryover alone was not sufficient. It appears that in the absence of Lyt-2+ suppressor T cells, antigen-specific help might be generated in donor cultures (Lyt-2-depleted MLC) which promoted or recruited the generation of antigen-specific CTL in host culture.

Analysis of T-cell subsets in rejection of Kb mutant skin allografts differing at class I MHC

The T-cell subpopulations which initiate and mediate tissue allograft rejection remain controversial. In the present study we attempted to identify the phenotype and function of the T-cell subset(s) primarily responsible for the rejection of skin allografts differing at a single class I locus in the major histocompatibility complex (MHC). We found that the rejection rates by B6 mice (H-2b) of four different class I mutant (Kbm) skin allografts form a distinct hierarchy. This hierarchy correlates strikingly and uniquely with the relative precursor frequencies of Lyt2+ interleukin-2-secreting T-helper cells reactive against the various Kbm mutants. To investigate the role of Lyt2+ T cells in the rejection of class I-disparate skin allografts directly, H-2b nude mice were engrafted with Kbm skin allografts and then reconstituted with L3T4+ or Lyt2+ T-cell subpopulations from syngeneic H-2b mice. Lyt2+ T cells were observed to be both necessary and sufficient for the rejection of class I-disparate Kbm skin allografts, whereas L3T4+ T cells were neither necessary nor sufficient. These results identify the Lyt2+ interleukin-2-secreting T-cell subset as the critical cell type determining the rejection rate of class I-disparate Kbm skin allografts.

Modification of suppressor/cytotoxic and helper subsets in lentil lectin-pretreated mice

The effect of lentil lectin (LCA) on various lymphocyte subpopulations in the spleen, lymph nodes and thymus of CBA mice was studied. The most marked effect after five 1-mg LCA doses was observed in the spleen. LCA caused a drop in both the total and relative number of cells carrying all the markers examined, i.e., Thy 1, L3/T4a, Lyt 2, and sIg, so that large numbers of lymphocytes did not express any of them. A dramatic decrease in the Thy 1-positive cell number is mainly due to depletion of the L3/T4a (helper) T cell subpopulation, whereas the Lyt 2+ (suppressor/cytotoxic) cells are less affected. The decrease in the Thy 1+, Lyt 1+ and L3/T4a+ cell numbers in the thymus and lymph nodes is smaller, the percentage of Lyt 2+ cells is even increased after LCA treatment. Our results indicate that two mechanisms play a role in the induction of allotransplantation tolerance by LCA: 'depletion' of helper T cells and a relative increase in the regulatory (suppressor) cell ratio, which may support allograft survival.

Experimental strategies for the study of cellular immunity in renal disease

This overview has examined some of the current experimental options available for the study of cellular immunity in the immunopathogenesis of renal disease. T cell immunity, where it has been examined, seems to have a particularly pivotal role in orchestrating and regulating functional patterns of renal injury. The use of the research methods presented here for the study of cell-mediated interactional events in kidney disease, however, has lagged behind similar efforts in other organ systems. We hope, therefore, this report will serve to stimulate and strengthen further interest in the cell biology of the nephritogenic immune response.

Transformation of T-lymphoid cells by Abelson murine leukemia virus

Abelson leukemia virus (A-MuLV) is an oncogenic murine retrovirus whose genome contains sequences homologous to those of a normal cellular gene, c-abl. It has been demonstrated to cause rapid transformation of several cell types, including pre-B lymphocytes, macrophages, and fibroblasts. More recently, A-MuLV has been reported to induce thymic tumors in a mouse strain (C57BL/Ka) previously thought to be resistant to disease induction. We showed that the masses occurring after intrathymic injection of the virus were composed of lymphocytes of a previously described immature T-cell phenotype. This phenotype has been defined here by flow cytometry of 10 primary tumor samples stained with antibodies to several thymocyte differentiation antigens. Hybridization of DNAs from these tumors with v-abl, immunoglobulin mu, and T-cell antigen receptor beta-chain probes confirmed the T-lymphoid, polyclonal nature of the primary tumor cells. The primary tumors were malignant, as clearly shown by reinjection into Thy-congenic host animals. Further, four Thy- in vitro cell lines derived from three tumors differed from the majority of primary tumor cells and were similar to previously described A-MuLV-transformed pre-B cells. The consistent T-lymphoid phenotype exhibited by primary A-MuLV thymomas may represent one stage of normal thymocyte differentiation.

Purinergic modulation of T-lymphocyte activation: differential susceptibility of distinct activation steps and correlation with intracellular 3',5'-cyclic adenosine monophosphate accumulation

The mechanism by which purinergic agonists modulate murine T-lymphocyte activation and proliferation was investigated. Adenosine and other compounds such as ATP and 2-chloroadenosine (ClAdo) were found to block T-cell mitogenesis induced by concanavalin A (Con A) in a dose-dependent fashion. The nonmetabolizable adenosine analog ClAdo was the most potent agent capable of inhibiting T-cell mitogenesis. Extracellular addition of the permeable cAMP analog dibutyryl cyclic AMP (dbcAMP) also led to a dose-dependent blockade of T-cell mitogenesis, although with less efficiency when compared to ClAdo. Addition of IL-2-enriched fluids failed to reverse blockade of T-cell mitogenesis by ClAdo or dbcAMP. ClAdo blocked T-cell enlargement induced after 20 hr of culture with Con A. We analyzed the effect of micromolar concentrations of ClAdo on interleukin-2 (IL-2) production, expression of IL-2 receptors (7D4 and 3C7 surface antigens), and induction of IL-2 responsiveness after in vitro cultivation with Con A. ClAdo inhibited both IL-2 secretion and induction of IL-2 responsiveness up to control levels in the same dose range it inhibited T-cell mitogenesis. However, cell surface expression of IL-2 receptors was not affected. Short incubations of resting splenic T cells with ClAdo led to a dose-dependent accumulation of cyclic AMP in responding cells. This effect was markedly reduced by the purinergic antagonist 3-isobutyl-1-methylxanthine (IBMX) but was not prevented by the adenosine uptake blocker dipyridamole. ClAdo elicited cAMP accumulation in the same dose range it inhibited T-cell activation events. Extracellular administration of dbcAMP to splenic T cells stimulated by Con A mimicked the effects of ClAdo on T-cell activation parameters, as revealed by a dose-dependent blockade of both IL-2 secretion and IL-2 responsiveness induction, without affecting IL-2 receptor expression. Short incubations of Con A-activated T-cell blasts with ClAdo also led to a dose-dependent accumulation of cAMP. We then analyzed the effect of purines and dbcAMP on IL-2-mediated activated T-cell growth. Purines caused a dose-dependent inhibition of IL-2-mediated T-cell proliferation and ClAdo was the most potent purinergic agonist tested. The effect of ClAdo on Con A-induced T blasts was shifted to the right, if compared to earlier T-cell activation steps.(ABSTRACT TRUNCATED AT 400 WORDS)

Fractionation of detergent lysates of cells by ammonium sulphate-induced phase separation

A procedure is described for fractionating detergent lysates of cells based on the ability of (NH4)2SO4 to induce phase separation of detergents such as Triton X-100, sodium deoxycholate, and sodium cholate, into detergent-rich and detergent-depleted phases. An analysis of six murine lymphocyte cell surface molecules revealed that the partitioning in Triton X-100 of each molecule was highly dependent upon the (NH4)2SO4 concentration, each antigen partitioning into the detergent-rich phase at a defined salt concentration. In contrast, none of the six molecules appeared in the detergent-rich phase of a Triton X-114 phase separation, even though two of the molecules, namely Ly-2/3 and L3T4, are well-characterized integral membrane proteins. It was also observed that (NH4)2SO4 resulted in the partitioning of many nonmembrane proteins into the detergent-rich phase, indicating that the procedure can be used to fractionate all cellular proteins. By judicious choice of (NH4)2SO4 concentrations, precipitation of cellular proteins at two different (NH4)2SO4 concentrations, and combining the method with subcellular fractionation prior to detergent solubilization, substantial enrichment and concentration of particular cellular proteins could be achieved.

Role of L3T4 antigen in the activation of various functions of Lyt-1+2- T cells against vaccinia virus

The present study defines assay systems for vaccinia virus-reactive Lyt-1+2- T cells mediating various functions and investigates the positivity of L3T4 antigen on these Lyt-1+2- T cells as well as the role of L3T4 antigen in the activation of these T cells with respect to their functions. C3H/He mice were immunized against vaccinia virus by inoculating viable virus intraperitoneally (i.p.). Anti-vaccinia virus reactivity in lymphoid cells from these immunized mice was assessed by proliferative response, helper T cell activities involved in cytotoxic T lymphocyte (CTL) and B cell (antibody) responses, delayed type-hypersensitivity (DTH) response, and production of lymphokines such as interleukin 2 (IL2) and macrophage-activating factor (MAF). The results demonstrate that all of the above anti-vaccinia virus responses were mediated by Lyt-1+2- T cells and that these Lyt-1+2- T cells expressed L3T4 antigens on their cell surfaces. Moreover, such anti-vaccinia Lyt-1+2- T cell responses were inhibited in the presence of anti-L3T4 antigen antibody. These results indicate that there is a reciprocal relationship between Lyt-2 and L3T4 markers, and that L3T4 antigen is closely related to the activation of various functions of anti-vaccinia virus Lyt-1+2- T cells.

Autoreactive T cell clones from mice infected with Mycobacterium bovis, strain Bacillus Calmette-Guérin (BCG). I. Phenotype, specificity and in vitro function

Mice were infected with the intracellular microorganism, Mycobacterium bovis BCG, and draining lymph node cells were collected. A T cell line was established which was cultured in the presence of syngeneic accessory cells (AC) and killed BCG. Stimulation of this line depended on syngeneic accessory cells and did not require BCG as a source of antigen, indicating that it was autoreactive. T cell clones derived from this line had the L3T4 helper/inducer phenotype and reacted with self-Ia on syngeneic macrophages or B cell blasts. Cloned T cells were also stimulated by syngeneic accessory cells pretreated with the lysosomotropic agent chloroquine and by H-2 compatible, background gene disparate, accessory cells, suggesting that they were specific for self-Ia. After in vitro stimulation, the T cell clones secreted interleukin 2 (IL 2) and interferon-gamma (IFN-gamma), helped B cells in antibody production and activated macrophages for secretion of reactive oxygen metabolites.

The mechanism of antigen presentation by dendritic cells and splenic adherent cells in the induction of an allogeneic cytotoxic T-lymphocyte response to H-2Kk liposomes

Induction of an allogeneic cytotoxic T-lymphocyte (CTL) response to purified alloantigen is partially dependent on uptake and processing of the class I alloantigen by antigen-presenting cells (APC) followed by recognition of the alloantigen and self Ia by helper T cells (TH). The activated TH provides the helper signal(s) to the alloantigen-specific CTL for proliferation and differentiation into an active effector CTL. The role of antigen processing and presentation of major histocompatibility complex alloantigens was examined and the ability of different types of APC to present purified H-2Kk liposomes was investigated. Splenic adherent cells (SAC), splenic dendritic cells (DC), and B-cell lymphoblastoid lines were all shown to be effective in the presentation of H-2Kk liposomes. The relative ability of these cells to serve as APC was determined to be DC greater than B-cell tumors greater than SAC. The role of processing of H-2Kk liposomes by SAC and DC was examined by investigating the effect of weak bases on pulsing of the APC. These experiments suggest that presentation of alloantigen by both SAC and DC involves a step which is sensitive to inhibition by weak bases. We examined whether the TH were activated by similar mechanisms when stimulated by the various APC. The functional involvement of the T-cell surface marker L3T4 was demonstrated in the induction of TH. In contrast, L3T4 was not involved in the subsequent generation of CTL since monoclonal antibody (MAb) specific for L3T4 was not effective in blocking CTL function in the presence of nonspecific T helper factor (THF). Similarly, Ia on the APC was shown to be involved in the stimulation of the TH pathway but not directly in the differentiation of the CTL. Thus, DC and B cells in addition to SAC can present H-2Kk to TH. The presentation of alloantigen by both cell types may involve an intracellular route as demonstrated by the blocking of the TH response by weak bases. Both Ia and L3T4 are required on the APC for induction of the TH response. The minimal requirements for activation of the CTL were H-2Kk liposomes and a source of THF.

Developmental potential and dynamic behavior of hematopoietic stem cells

We have used retrovirus-mediated gene transfer to mark hematopoietic stem cells in vitro and have tracked the fate of these cells after their transplantation into lethally irradiated recipients. Several classes of stem cells are demonstrated, including cells whose progeny completely repopulate all hematopoietic lineages as well as cells that contribute predominantly to certain lineages or to specific anatomical locations. In a majority of recipients, we find that few (1 or 2) stem-cell clones account for the majority of the mature hematopoietic cells. These results coupled with retransplantation studies suggest an in vivo mechanism for the temporal control of stem-cell use. Further studies based on periodic sampling of primary recipients suggest that normal hematopoiesis results from the sequential activation of different stem-cell clones rather than from an averaged contribution of the entire stem-cell pool.

The gene encoding the T-cell surface protein T4 is located on human chromosome 12

The surface glycoproteins T4 and T8 define functionally distinct populations of T lymphocytes. We have obtained cDNA and genomic clones encoding the T4 molecule and used these as probes to determine the chromosomal location of this gene. Genomic blotting experiments, along with in situ hybridization analyses, indicate that the T4 gene resides on the short arm of human chromosome 12, at region p12-pter. Thus, the T4 gene is not linked to any known member of the immunoglobulin gene family, including its counterpart gene, T8, which resides on human chromosome 2 immediately distal to the immunoglobulin kappa locus.

Partial primary structure of the T4 antigens of mouse and sheep: assignment of intrachain disulfide bonds

The T4 antigens of mouse and sheep have been purified to homogeneity and partially sequenced using protein and peptide microsequencing techniques. Both mouse and sheep antigens bear distinct homology to human T4, having an amino-terminal segment that is homologous to the K-chain variable region (VK). A surprisingly high degree of sequence divergence was nevertheless evident between the T4 antigens of the three mammalian species, suggesting an unusually rapid rate of evolution that is possibly related to the functional role of T4 in class II major histocompatibility complex antigen recognition. The mouse and sheep T4 antigens contain at least three intrachain disulfide bonds which in all cases connect adjacent cysteine residues. All three intrachain disulfide linkages are situated within the putative extracellular domain, and the amino-terminal disulfide bond probably involves the two cysteine residues homologous to those which form the intrachain bridge within the VK domain of immunoglobulin molecules. The structural relationship of the T4 antigen to other members of the immunoglobulin supergene family is discussed.

Inhibition of rat autoimmune T cell activation by monoclonal antibodies

The essential requirement for adoptive transfer of autoimmune diseases such as experimental allergic encephalomyelitis (EAE) by T lymphoblasts from established T cell lines, is a prior activation of these cells by autoantigen or mitogen. We have investigated the possibility of modulating this activation process by using monoclonal antibodies directed against rat leukocyte differentiation antigens. We report here that antigen-driven activation of autoimmune, encephalitogenic T cells from established myelin basic protein (MBP)-specific rat T cell lines can be inhibited by some, but not all, antibodies against RT1.B Class II restriction elements. In addition, monoclonal antibodies with specificity for rat leukocyte common antigen (OX-1) and T cell differentiation antigens W3/13 and W3/25 are inhibitory, while monoclonal antibody OX-8 with specificity for T cytotoxic/suppressor cells has no effect. We also observed that concanavalin A-induced activation of the T cells is more resistant to the inhibitory effect of monoclonal antibodies, and can be blocked effectively only by antibody OX-1. This demonstration that autoimmune T cell function can be inhibited by monoclonal antibodies points the way in suggesting cellular targets for immunotherapeutic purposes.

T-cell receptor variable region gene usage in T-cell populations

We have examined T-cell receptor alpha- and beta-chain variable (V) region gene usage in T-cell populations predicted to have different major histocompatibility complex-restriction specificities. Using a sensitive ribonuclease protection assay to measure T-cell receptor mRNA levels, we found no striking differences in the usage of three V alpha genes and three V beta genes in T-cell populations from three congeneic H-2-disparate strains of mice and between the mutually exclusive Ly2+ L3T4- and Ly2- L3T4+ T-cell subpopulations. These results suggest that major histocompatibility complex restriction cannot be explained by the differential usage of nonoverlapping V alpha or V beta gene pools. In contrast, striking but unpredictable differences were seen in V gene usage in populations of T cells selected by activation with particular alloantigens.

Functions of purified L3T4+ and Lyt-2+ cells in vitro and in vivo

The expression of L3T4 and Lyt-2 cell surface molecules separates T cells into two broad, non-overlapping subsets: typical T helper cells are L3T4+ Lyt-2- whereas most T killer cells and their precursors are L3T4- Lyt-2+. This review compares highly purified populations of unprimed L3T4+ and Lyt-2+ cells for their capacity to respond to class I vs. class II H-2 alloantigens. Various parameters are considered, including generation of mixed lymphocyte reactions (MLR) and cell mediated lympholysis (CML) in vitro, proliferative responses in irradiated mice, graft-versus-host reactions and skin allograft rejection. In all of these assays the two T cell subsets exhibit marked specificity in their response to H-2 alloantigens, L3T4+ cells responding only to class II and not class I differences and Lyt-2+ cells showing reciprocal specificity. Contrary to current dogma, the bulk of the evidence suggests that primary responses of Lyt-2+ cells do not depend on exogenous help provided by other T cells.

Control of hemopoiesis in mice by sensitized L3T4+ Lyt2-lymphocytes during infection with bacillus Calmette-Guérin

When injected intravenously with bacillus Calmette-Guérin (BCG; 10(7) viable units), C57BL/6 mice rapidly develop a transient anemia associated with an increased number of granulocytes and monocytes, whereas C3H/He mice do not. Because these two features are lacking in C57BL/6 nude mice we postulated that T lymphocytes can regulate hemopoiesis during infection. To assess further the role in hemopoiesis of T lymphocytes present in bone marrow of C57BL/6 and C3H/He mice, the frequency of BCG-specific T lymphocytes and their surface marker phenotype were determined by limiting dilution analysis and use of monoclonal antibodies. The number of BCG-specific T lymphocytes was estimated to be 50- to 100-fold higher in bone marrow of C57BL/6 than in that of C3H/He mice. Although L3T4+ Lyt2-and L3T4- Lyt2+ BCG-specific T lymphocytes were generated in mice of both strains, in C57BL/6 mice L3T4+ cells were induced preferentially from day 1 through day 5 after infection in correlation with hemopoietic changes. The relation between T-cell immune response and hemopoietic changes was substantiated by results obtained after in vivo treatment with monoclonal antibodies. Selective depletion of L3T4+ T cells by in vivo injection of anti-L3T4 monoclonal antibodies (GK 1-5) inhibited the development of the anemia and the related increased production of phagocytes in C57BL/6 mice receiving BCG.

Analysis of the function of L3T4+ T cells by in vivo treatment with monoclonal antibody to L3T4

We have used MAb to L3T4 to examine the function of L3T4+ T cells in normal and autoimmune mice. Treatment of mice with MAb to L3T4 profoundly depleted L3T4+ cells from the blood, spleen, and lymph nodes, but not the thymus. In BALB/c and C57BL/6 mice, selective depletion of L3T4+ cells blocked both primary and secondary humoral immune responses and inhibited, but did not prevent, cellular immune responses. In lupus-prone B/W and BXSB mice, depletion of L3T4+ cells significantly retarded autoimmune disease. Because the L3T4 antigen in mice is homologous to the CD4 antigen in humans, these findings have implications regarding the function of CD4+ T cells and the prospects for using MAb to CD4 as therapeutic agents.

Antigen presentation by liposomes: inhibition with antibodies

The involvement of both antigen and class II major histocompatibility complex (MHC) molecules in T cell activation by liposome-bound antigens was investigated. We used a pigeon cytochrome c (PCC)-specific Ek-restricted T cell hybridoma that can be activated to produce interleukin 2 by liposomes carrying either PCC and Ek molecules, or a high concentration of PCC alone. We demonstrated that the MHC-restricted response of this hybridoma to liposomes is specifically blocked by both anti-MHC and anti-PCC monoclonal antibodies, whereas unrestricted activation is only inhibited by PCC-specific antibody.

Tolerance to rat monoclonal antibodies. Implications for serotherapy

The antiglobulin response is a major complication of mAb therapy. It has been suggested that, in clinical practice, this might be avoided by using human or chimeric mAbs, or by prior induction of tolerance to the therapeutic mAb. In this study, we show that it is possible to induce tolerance in mice to the constant regions of rat IgG2b mAbs by both classical deaggregation methods and by anti-L3T4 mAb therapy. Mice tolerant to IgG2b constant region determinants failed to make an antiglobulin response when immunized with a number of mAbs of the same isotype that had no binding specificity for mouse cells, but produced vigorous antiidiotypic responses to cell-binding mAbs. Binding of antibodies to hemopoietic cells rends their idiotypic determinants major immunogens even in the presence of tolerance to constant region epitopes. These findings suggest that the use of human or chimeric mAbs will not be sufficient to eliminate the antiglobulin response, and that additional methods need to be investigated.

In vitro granuloma formation using defined antigenic nidi

The in vitro granuloma model provides an excellent tool to study granulomatous hypersensitivity. In our studies of granuloma formation in schistosomiasis, we have demonstrated the utility of the model with respect to analysis of human PBL responses, cloned T cells, purified antigens of the parasite, and regulatory mechanisms. We have also presented data which demonstrate the applicability of this model to other antigenic systems. While the suggestion that this model may be suitable for the study of sarcoidosis may be premature, we would propose that the system may be adapted to screen potentially causative antigens. Furthermore, with the identification of the critical antigen(s), the in vitro granuloma model will facilitate studies at the clinical level.

Mechanisms of lymphocyte adhesion to human vascular endothelial cells in culture. T lymphocyte adhesion to endothelial cells through endothelial HLA-DR antigens induced by gamma interferon

The effects of interferons (IFNs) on lymphocyte adhesion to cultured human vascular endothelial cells (EC) were investigated using an in vitro assay. Endothelial cells obtained from umbilical vein were first cultured at a low density with a conditioned medium (CM) from 12-O-tetra decanoylphorbol 13-acetate-concanavalin A (TPA-Con A) stimulated human peripheral blood lymphocytes (PBL), or with recombinant (r) gamma interferon (IFN-gamma) or r alpha interferon (IFN-alpha), and then were incubated with freshly isolated PBL. Natural IFN-gamma in the TPA-Con A CM and rIFN-gamma (12.5-500 U/ml) induced major histocompatibility complex-class II antigens (HLA-DR, HLA-DP, and HLA-DQ) and significant lymphocyte adhesion to the EC, whereas rIFN-alpha did not. The lymphocyte adhesion to the EC and the expression of DR antigens on the EC were well correlated in terms of both kinetics and the dose-response pattern of rIFN-gamma. When EC expressing I region associated (Ia) antigen were preincubated with monoclonal anti-DR antibody before the addition of lymphocytes, the lymphocyte adhesion was significantly inhibited in both allogeneic and syngeneic combinations, whereas anti-HLA-DP, anti-HLA-DQ, and anti-HLA-ABC antibodies did not inhibit the binding at all. Cell fractionation experiments indicated that the majority of lymphocytes adhering to Ia-expressed EC were Leu-3+ T cells, whose binding was again almost completely inhibited by anti-DR antibody. Moreover, anti-Leu-3a, but not anti-Leu-2a, antibody effectively inhibited the T cell adhesion to the EC. These results strongly suggest that the interaction of the Leu-3(T4) receptor of T cells with IFN-gamma-induced DR antigens on EC plays a central role in the selective adhesion of Leu-3+ T cell to EC.

Induction of tolerance by monoclonal antibody therapy

A major goal in immunology has been to find a means of selectively abolishing an individual's potential to mount an immune response to certain antigens, while preserving responsiveness to others. The facility to induce such specific immunological unresponsiveness in an adult would have major implications for tissue-grafting, the control of allergy and for treatment of autoimmune disease. Classical work has shown that immunosuppressive regimes, such as irradiation, anti-lymphocyte globulin or thoracic duct drainage, may facilitate tolerance induction. We describe here a technique by which the immune system of mice can be manipulated to be tolerant to certain protein antigens by administering these during a brief pulse of treatment with a monoclonal antibody directed to the L3T4 molecule on helper T lymphocytes. This technique has the potential to form the basis of a novel generalized means of tolerance induction.

T-lymphocyte differentiation and the extracellular matrix: identification of a thymocyte subset that attaches specifically to fibronectin

A population of murine thymocytes adheres specifically to fibronectin but not to vitronectin, laminin, or collagen type I. The interaction of these thymocytes with fibronectin could be inhibited by the synthetic peptide Gly-Arg-Gly-Asp-Ser-Pro, which comprises the previously identified cell-attachment determinant of the molecule, suggesting that the cell attachment site on fibronectin is recognized by these cells. A similar peptide, in which the aspartate residue had been replaced with glutamate, had no effect on this adhesion. The fibronectin-adherent thymocytes were found to be cortisone-sensitive; to bind peanut agglutinin; to have a Thy-1.2+, Ia- surface phenotype; and to express H-2 antigen only weakly on their surface. In addition, approximately 80% of the fibronectin-adherent cells expressed L3T4 and 80% expressed Ly-1 on their surface, whereas greater than 95% were positive for Ly-2. The data suggest that these cells, which constitute 10% of all thymic lymphocytes, are cortical thymocytes. We propose that their adhesion to fibronectin may be important for their differentiation. The binding to fibronectin provides a means to selectively isolate these cells for study.

Production and characterization of cloned T-cell hybridomas that are responsive to Rickettsia conorii antigens

T-cell hybridomas produced by the fusion of Rickettsia conorii immune T cells to the AKR thymoma BW 5147 produced interleukin-2 when stimulated with the antigens of three different R. conorii strains. One cloned hybridoma responded only to R. conorii antigens, whereas a second and third cloned hybridoma also responded to the antigens of Rickettsia rickettsii Sheila Smith and Rickettsia sibirica 246, respectively. Antigen responses required antigen-presenting cells, and this interaction was major histocompatibility complex restricted. Fluorescence-activated cell-sorter analysis demonstrated that all three hybridomas were of the Thy-1.2+, Lyt-2- phenotype and that two of the three were L3T4+. These data demonstrated the presence of an antigenic epitope that is R. conorii species specific and other epitopes that are common to various members of the spotted fever group which can stimulate interleukin-2 production by T-cell hybridomas.

Involvement of Lyt-2 and L3T4 in activation of hapten-specific Lyt-2+ L3T4+ T-cell clones

The murine T-cell surface molecules Lyt-2 and L3T4 play a role in the activation of antigen-specific T cells. The currently accepted model for the function of these molecules proposes that Lyt-2 and L3T4 increase the overall avidity of the interaction between the T-cell antigen receptor and antigen in association with the major histocompatibility complex (MHC) molecules on the antigen-presenting cell. We have used two unusual Lyt-2+ L3T4+ class II MHC-restricted T-cell clones to test whether Lyt-2 can substitute for L3T4 when the T-cell antigen receptor is class II MHC-restricted. Monoclonal antibodies against L3T4 profoundly inhibited antigen-induced lymphokine production by both T-cell clones. Anti-Lyt-2 monoclonal antibody had no effect. These results strongly suggest that L3T4 and the class II-restricted T-cell antigen receptors are physically close during antigen recognition, probably as part of a multimolecular complex from which Lyt-2 is excluded. The ability of L3T4 but not Lyt-2 to participate in such a complex with class II-restricted T-cell antigen receptors may explain the striking correlation between class II restriction and L3T4 expression in the peripheral T-cell pool.

Cloned cytotoxic T lymphocytes that recognize an I-A region product in the context of a class I antigen

Cloned CTLs QM3 and QM7 isolated from a bulk CTL line B10.QBR anti-B10.MBR recognized a combination of the H-2Kb molecule and an I-Ak subregion gene product. Such a combinatorial specificity was revealed by complementation of the target antigen in F1 animals between two negative parental strains carrying H-2Kb and I-Ak, respectively. We confirmed the involvement of the H-2Kb molecule by blocking killing with anti-Kb mAb and failure of certain mutant H-2Kb genes to complement with I-Ak to generate the determinant in F1 animals. Although the nature of the I-Ak subregion gene product is not definitive, there was a correlation between the expression of Ia antigens on the cell surface and susceptibility of the cells to lysis by these CTLs, suggesting that it is the classical I-Ak class II antigen.

Characterization of two distinct primary T cell populations that secrete interleukin 2 upon recognition of class I or class II major histocompatibility antigens

This study has characterized the primary T cell subpopulations that secrete IL-2 in response to recognition of either class I or class II MHC encoded determinants. The addition to culture of anti-IL-2-R mAb inhibited the consumption of IL-2 by activated lymphocytes during the response period, permitting a much more accurate assessment of the amount of IL-2 produced in the response cultures. Using this response system, we found that primary T cell populations contain two IL-2-secreting T cell subsets that express reciprocal phenotypes and different MHC recognition specificities: an L3T4+, Lyt-2- T cell subset responsive to both class I and class II MHC alloantigens, and an L3T4-Lyt-2+ T cell subset responsive only to class I MHC alloantigens. The L3T4+ T cell subset expressed a broad functional response repertoire in that L3T4+ T cells were triggered to secrete IL-2 upon recognition of unmodified self-Ia determinants, allogeneic Ia determinants, and class I alloantigens presented by self-Ia determinants. The activation of L3T4+ IL-2-secreting T cells, even those responsive to class I MHC alloantigens, could be blocked completely by anti-Ia mAbs, confirming that the L3T4+ T cell subset was in fact class II restricted. In contrast, the Lvt-2+ T cell subset expressed a narrow functional response repertoire in that they were triggered to secrete IL-2 only in response to allogeneic class I MHC determinants, and were not triggered to secrete IL-2 even in response to TNP-modified self-MHC determinants. The specificity of Lyt-2+ IL-2-secreting T cells for class I MHC allodeterminants was confirmed by the observations that: (a) their activation could be blocked completely by anti-class I mAbs, (b) they could be triggered by Ia- cell lines which expressed class I MHC alloantigens and possessed accessory function, and (c) they responded to class I MHC alloantigens but failed to respond to class II MHC alloantigens, even in the presence of exogenously added second signals that circumvented the requirement for alloantigen-bearing accessory cells. Finally, the frequency of primary Lyt-2+ T cells that secreted IL-2 in response to class I (Kbm1) MHC alloantigens was shown to be only minimally lower than that of L3T4+ T cells that secreted IL-2 in response to class II (I-Abm12) MHC alloantigens.(ABSTRACT TRUNCATED AT 400 WORDS)