Inhibition of specific cell-mediated cytotoxicity by anti-T-cell receptor antibody

Specific suppression of MLC and CML by anti-idiotypic antibodies in the mouse

Rabbit antisera directed against idiotypic determinants of alloreactive mouse CBA anti-C57BL/6 T blasts were raised in the following manner: first, a rabbit serum directed against nonspecific CBA blasts cells was prepared by injecting CBA concanavalin A blasts three times at monthly intervals into a rabbit. Second, specific CBA anti-C57BL/6 T lymphoblasts were induced in a mixed lymphocyte culture (MLC), were purified by gravity sedimentation through a fetal calf serum gradient, and, finally, were incubated with the anti-blast serum from the first step. During this incubation, presumably all epitopes of the blast cell population were blocked by anti-blast antibodies, except for the greatly amplified set of CBA anti-C57BL/6 alloreactive idiotypes. The mixture was then injected into fresh rabbits, which were boosted with similar mixtures after 3 and 6 weeks. Blood samples were removed 10 days after each injection. Such sera, when used together with complement, inhibited specifically the stimulation of CBA cells by C57BL/6 antigens in MLC and the CBA anti-C57BL/6 killer cells.

Studies on the induction and expression of T-cell-mediated immunity. XIII. Membrane-associated antigens of cytotoxic T lymphocytes involved in cytotoxicity

An xenogeneic rat anti-mouse T-cell serum, designated RAT*, has been shown to block the cytolytic activity of cytotoxic T lymphocytes (CTL) at a postbinding step. RAT* serum or the IgG fraction was extensively absorbed with the target cell, P815, a DBA mastocytoma, and used with or without further absorption to immunoprecipitate specific molecules from radiolabeled membrane extracts of CTL derived from either in vivo-allosensitized mice or from cytotoxic clones maintained in in vitro cultures. Cell surface sialic acid residues were labeled by oxidation with sodium periodate (NaIO4) and reduction with tritiated sodium borohydride ([3H]NaBH4). Alternatively, cell surface proteins were labeled with 125I by lactoperoxidase-catalyzed iodination. Nonidet P-40 (NP-40)-solubilized radiolabeled membranes were then immunoprecipitated with RAT* serum and analyzed by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE). Three membrane-associated molecules of 95,000, 140,000 and 180,000 Mr were found by such analysis. The sensitivity of these three molecules to trypsinization and their susceptibility to labeling with [3H]NaBH4 suggested that they are glycoproteins. Moreover, when RAT* serum or the IgG fraction was absorbed with various cell types, its ability to immunoprecipitate the three molecules correlated with its ability to block cytolysis. Adsorption of RAT* serum with CTL, but not with nonimmune thymocytes, significantly reduced the ability of RAT* serum to inhibit cytotoxicity and to immunoprecipitate the 95k, 140k, and 180k molecules. Thus, these findings suggest that one or more of these cell surface molecules of CTL may be involved in the cytolytic process.

Lymphoid cell surface interaction structures detected using cytolysis-inhibiting monoclonal antibodies

We screened monoclonal antibodies obtained by xenogeneic immunization for their capacity to inhibit T cell-mediated cytolysis. These antibodies fell into two classes according to the cell structures they recognized, of 30-35 K and 94-180 K apparent molecular weight, respectively. The main features of these structures and of their interaction with the corresponding antibodies were reviewed. The inhibition of cytolysis by these antibodies was shown to occur mainly at the effector cell level, at the recognition stage of cytolysis, and to depend on the nature of target cells, effector cells, and link between these cells. T cell functions other than cytolysis were also inhibited by some of these antibodies. We considered various possible mechanisms to account for the inhibition of cytolysis by these mAb. We favor an hypothesis based on inhibition by these mAb of lymphoid cell surface interaction structures. This hypothesis was discussed within the general framework of cell interaction structures in immunological and non-immunological experimental systems.

The molecular basis for cytolytic T lymphocyte function: analysis with blocking monoclonal antibodies

During the past decade the mechanism of CTL-mediated killing has been resolved into 3 steps, and its cation requirements, and general nature have been well defined. However, biochemical understanding of the CTL-target interaction has made little progress. Recently, we have developed a monoclonal antibody (MAb) which blocks killing by binding to a previously undescribed molecule on the CTL membrane, a molecule which we therefore have termed lymphocyte function-associated antigen one (LFA-1). LFA-1 and Lyt-2,3 are the only presently identified sites for such blocking; antibodies to over a dozen other molecules expressed on the CTL do not block killing. Present evidence suggests that LFA-1 is crucial in the adhesive interaction of T cells with other cells (e.g., targets, macrophages, perhaps B cells) The continuing search for blocking MAbs provides a systematic way to link specific molecules with CTL function.

T cell receptors with allo-major histocompatibility complex specificity from rat and mouse. Similarity of size, plasmin susceptibility, and localization of antigen-binding region

Antisera specific for the constant part Ctau of T cell receptor molecules in mice and rats have been produced in rabbits by immunization with idiotype-positive rat T cell molecules. Such antisera could be shown to react with the majority of normal T lymphocytes from both rats and mice. Mixed leukocyte culture-activated T blasts displayed a higher percentage of positive cells than concanovalin A- or phytohemaglutinin-induced T blasts. Lipopolysaccharide-induced B blasts were not reactive with the antiserum. Lyt-1-,2+,3+ blasts displayed a significantly brighter straining than the corresponding Lyt-1+,2-,3- blasts. Isolation of the reactive molecules from T cells by immunosorption yielded a 70,000-dalton single chain polypeptide as the dominant group of molecules. Plasmin caused the chain to split into 45,000- and 25,000-dalton polypeptides, with the smaller fragment displaying antigen-binding capacity. Molecules identical in size and plasma degradation patterns were isolated from Lyt-1+,2-3- and 1-,2+,3+ blasts. Preliminary functional data supported the view that the antiserum is directed against the constant region Ctau relevant receptor structures on immunocompetent T lymphocytes.

Rabbit antisera with specificity for isolated mouse T-lymphocyte receptors

Rabbit antibodies obtained after immunization of mouse immunoglobulin (MIg)-tolerant rabbits with B6 anti-CBA IgG and having specificity for B6 anti-CBA IgG and T-cell receptors (antiserum 5936) were used to isolate 5936-reactive molecules from B6 anti-CBA mixed lymphocyte culture supernatants. Such 5936-reactive molecules were produced by the B6 T cells, and they did not react with rabbit anti-MIg antisera. They had a mol. wt of 50,000-75,000, and were single-chain polypeptides that did not react with concanavalin A (Con A)--Sepharose. These molecules were in turn injected into rabbits, and the antisera thus obtained had the following characteristics: (1) they reacted against B6 anti-CBA T-cell receptor material but not against B6 anti-CBA IgG; (2) they reacted with about 35% of B6 (H-2b, Ig-1b) anti-CBA T cells, 25% of B6 Con A blasts and 0-10% of normal B6 T cells but not with B6 lipopolysaccharide (LPS) blasts, C3H.B10 (H-2b, Ig-1j) anti-CBA or CBA anti-B6 T cells, CBA Con A blasts or normal CBA T cells; and (3) they reacted with the same 50,000-75,000 mol. wt, T-cell-derived molecules as did antiserum 5936. The implications of these findings are discussed in relation to the nature of T-cell receptors.

Inhibition of cell-mediated lysis by xenoantibodies reactive with effector T lymphocytes

The aim of the present study was to determine whether rabbit antisera against various murine tissue antigens contain antibodies that affect the activity of cytotoxic T lymphocytes in the absence of complement. Following heat inactivation, the xenoantisera were absorbed with mouse liver and kidney and tested for their capacity to inhibit cell-mediated lysis (CML). In the presence of complement (C), rabbit anti-brain antiserum (RABr), rabbit anti-thymus antiserum (RAT) and rabbit anti-boiled thymus antiserum (RABT) lysed effector T cells, and CML was abolished. In the absence of C, RAT maintained its strong inhibitory activity on CML, RABr had no inhibitory effect, whereas only some batches of RABT were effective. Monovalent Fab fragments of RAT inhibited CML as effectively as intact antibody molecules. The activity of RAT could be removed by absorption with T and B lymphocytes of various sources. Inhibitory antibodies could be removed by absorption with C3 H B lymphoma cells and upon elution from antibody-coated cells proved again highly effective in inhibiting CML. These results show that RAT contains antibodies which react with determinants shared by T and B lymphocytes and which block the activity of cytotoxic T cells.

The effect of xenoantisera on T-lymphocyte functions in the absence of complement

An attempt was made to determine whether xenoantisera can detect functional receptors on mouse T lymphocytes. Antisera were raised by immunizing rabbits with BALB/c thymus cells, boiled thymus homogenate, brain homogenate or bone marrow cells. Following heat inactivation these antisera were absorbed with mouse kidney and liver homogenates, and studied for their effect, in the absence of C', on the activity of murine T lymphocytes. Rabbit anti-bone marrow serum (RAB) had no effect on the mixed lymphocyte reaction (MLR) nor on cell-mediated lysis (CML). In contrast, rabbit anti-thymus serum (RAT) and anti-boiled thymus serum (RABT) inhibited strikingly, the MLR, CML, and the response to concanavalin A and phytohemagglutinin. Rabbit anti-brain serum (RABR) caused a marked increase of the proliferation of lymphocytes both in the presence or absence of various stimuli and had no effect on the CML. Absorption experiments indicated that a number of antigens are involved in the inhibitory activity of RAT. Antibodies to a T cell specific antigen interfere with the response of T lymphocytes to mitogenic stimuli, while the activity of cytotoxic T cells is inhibited by antibodies to a determinant shared by B and T lymphocytes.

Inhibition of the activity of cytotoxic murine T lymphocytes by antibodies to idiotypic determinants

The nature of the receptors on the surface of cytotoxic T lymphocytes (CTL), which enable these cells to recognize antigens on allogeneic targets, is still a matter of controversy. In the present study various mouse alloantisera were tested for their capacity to inhibit, in the absence of complement, the cytotoxic activity of sensitized peritoneal T lymphocytes. The only antiserum which, even after heat inactivation, consistently inhibited cytotoxic T lymphocytes was an antiserum elicited in (C3H X C57B1/6)F1 mice by immunization with AKR/Cum thymus cells. The serum inhibited the cytotoxic reaction of either AKR/J or AKR/Cum CTL on EL-4 target cells but had no inhibitory activity on the cytotoxic reaction of AKR/J cells against P-815 target cells. Thus the inhibitory activity of the serum could not be attributed to antibodies against Ly-3 determinants present in the serum. This conclusion was strengthened by the finding that the inhibitory activity of the serum could be removed by absorption, not only with AKR/J thymus cells but also with AKR/J bone-marrow cells, a procedure which did not affect the titre of Ly-3 antibodies. The serum failed to exert any inhibition on cytotoxic T lymphocytes of BALB/c and C3H mice reacting against EL-4 target cells, indicating that the inhibitory activity of the antiserum did not result from contamination by antibodies against C57B1 antigenic determinants. It was concluded that the inhibitory activity of the antiserum resulted from the presence of antibodies against idiotypic determinants expressed on AKR/Cum thymus cells reacting against the hybrid hosts. It seems, therefore, that idiotypic determinants expressed on the surface of cytotoxic T lymphocytes may be directly involved in their cytotoxic activity.

Surface glycoproteins of resting and activated human T lymphocytes

This review summarizes some recent studies on the surface glycoproteins of human thymocytes and T lymphocytes. Purified cells were surface labeled by the galactose oxidase-NaB3H4 or periodate-NaB3H4 techniques. The radioactive membrane glycoproteins were separated by polyacrylamide slab gel electrophoresis and visualized by fluorography. Thymocytes and T lymphocytes show characteristic surface glycoprotein profiles which are easily distinguishable from those of the other main groups of human leukocytes. We observed specific changes in the surface glycoprotein patterns which correlate with the degree of maturation and functional activation of T cells. Surface molecules carrying T cell specific antigens were identified by immune-precipitation from lysates of surface labeled thymocytes and T lymphocytes using rabbit anti-human T cell antibodies. Finally we describe a leukocyte membrane glycoprotein which is a precursor of serum alpha 1 acid glycoprotein (orosomucoid).

Mouse alloantibodies capable of blocking cytotoxic T-cell function. I. Relationship between the antigen reactive with blocking antibodies and the Lyt-2 locus

In an attempt to produce allonatibodies to cytotoxic T-cell receptors, hyperimmune anti-lymphocyte antisera have been raised in mice of various strain combinations, and have been tested for their ability to block allogeneic cell-mediated lymphocytotoxicity (CML) in the absence of complement at the T killer cell level. Most of the sera failed to show any significant and reproducible inhibitory effects. However, among C3H anti-B10.BR antisera, some sera were found to be capable of significantly inhibiting CML. This effect was attributable to antibodies reacting with the killer population rather than the target cells, because the sera inhibited B10 anti-C3H CML but not C3H anti-b10 CML. Among mouse strains tested, A/J, BALB/c, B10, and B6 strains were sensitive to the inhibitory effect of the sera whereas AKR, CBA, C3H, and DBA/2 strains were insensitive. The sensitivity of killer cells to the inhibitory effect correlated well with the strain distribution of the Lyt-2.2 antigen. In the presence of complement, these same sera were toxic to 100% of spleen cells of AKR, BALB/c, B10, and DBA/2 strains, with comparable cytotoxic titers. Thus, the inhibitory activity of the sera could not be explained by nonspecific effects of high-titered antibodies. To study the relationship between the antigen(s) responsible for the blocking effect and Lyt-2-linked genes, killer cells from Lyt-2 congenic strains were tested and conventional anti-Lyt-2.2 antisera were raised in an appropriate congenic strain combination. Killer cells from B6, but not from B6.Ly2.1 animals, were significantly sensitive to the blocking effects of the inhibitory C3H anti-B10.BR sera. The conventional anti-Lyt.2.2 sera did produce CML blocking, although there was no apparent correlation between such blocking and the anti-Lyt-2.2 cytotoxic titer. These results thus indicate that the target molecules responsible for blocking of killer cells are encoded or regulated by genes that are closely linked to or identical with Lyt-2.

Studies on the structure of T lymphocyte receptors using xenogeneic anti-idiotype antibodies

The present study is an attempt to produce xenogeneic anti-idiotype antibodies (Id) against mouse anti-H2 antibodies. The purpose is to obtain such anti-Id antibodies with reactivity against both B and T cells in quantities which will allow thorough investigation of the biochemical nature of the T cell receptor for alloantigen. Data are presented from experiments performed with an antiserum 5936 which was obtained after immunization with C57B1/6 anti-CBA antibodies.

Characterization of surface glycoproteins of mouse lymphoid cells

We have labeled exposed surface glycoproteins of mouse lymphoid cells by the galactose oxidase-tritated sodium borohydride technique. The labeled glyco-proteins were separated by polyacrylamide slab gel electrophoresis and visualized by autoradiography (fluorography). The major thymocyte surface proteins have molecular weights of 170,000 and 125,000. Thymocytes from TL antigen-positive mouse strains showed an additional band with a molecular weight of 27,000. Highly purified T lymphocytes contain two major surface glycoproteins with molecular weights of 180,000 and 125,000. Purified B lymphocytes have one major surface glycoprotein with a molecular weight of 210,000. When T lymphocytes are stimulated in vitro by concanavalin A or phytohemag-glutinin, the major proteins characteristic of T cells are relatively weakly labeled, but new components of lower molecular weights appear on the cell surface. A similar change is seen in B lymphocytes stimulated by Escherichia coli lipopolysaccharide. T lymphoblasts isolated from mixed lymphocyte cultures show a slightly different surface glycoprotein pattern. A polypeptide with a molecular weight of 57,000, which was labeled without enzymatic treatment by tritiated sodium borohydride alone, is strongly labeled in proliferating cells.

Cell-bound receptors for alloantigens on normal lymphocytes. II. Antialloantibody serum contains specific factors reacting with relevant immunocompetent T lymphocytes

The rat popliteal node graft-vs.-host assay was shown to depend on the presence of parental T cells in the inoculum. Antialloantisera raised in F(1) hybrid rats against alloantibodies of one parent directed at transplantation antigens of the other parent displayed some or all of the following specific effects on parental T cells: They inhibited local GvH by purified T-cell suspensions; they blocked the capacity of GvH-reactive cells to adsorb onto fibroblast monolayers of the relevant genotype; together with complement, they killed GvH-reactive cells.