Anti-self receptors. I. Direct detection of H-2L region-restricted receptors on murine thymocytes

Signal minus 1: a key factor in immunological tolerance to tissue-specific self antigens?

Recent data suggest that many autoreactive T cells, particularly to tissue-specific self antigens, can escape thymic deletion. The current dogma is that these autoreactive T cells are silenced by the failure of most tissues to provide co-stimulation (signal 2), antigen alone (signal 1) inducing T cell unresponsiveness. However, I propose that activation of autoreactive T cells frequently occurs but autodestruction by effector T cells is tightly regulated. This phenomenon is most evident with lymph node metastasizing tumour cells where the regional lymph node can mount a vigorous response to the invading tumour cells but tumour growth is unimpaired. I suggest that autodestruction is prevented by inhibitory receptors on T cells which recognize class I MHC structures on target cells. These receptors, which I propose deliver 'signal minus 1' to T cells, were recently described on NK cells and a subpopulation of peripheral T cells. They are also strikingly similar to a family of anti-self receptors that my laboratory described on murine T and B cells 15 years ago. In the 'signal minus 1' model, antigen-activated T cells acquire the inhibitory receptors when they become co-stimulation independent and gain the ability to exit lymphoid organs and enter non-lymphoid tissues. Thus, if autoreactive effector T cells encounter autoantigen in tissues they are functionally silenced by inhibitory receptor engagement and signal minus 1 delivery. In contrast, I propose that in response to intracellular infections, cells down-regulate expression of their ligands for inhibitory receptors. Such a model allows infected cells to be selectively eliminated by effector T cells. If correct, the model predicts that effector T cells, whether foreign-antigen- or autoantigen-specific, can selectively respond to infected cells. This apparent 'usefulness' of autoreactive T cells may explain their observed persistence even after an encounter with autoantigen. It is also suggested that signal minus 1 may silence autoreactive B cells specific for tissue-specific cell surface antigens and lack of signal minus 1 may partially explain the vigorous T cell response to allogeneic MHC. Finally, it is hypothesized that, in evolutionary terms, inhibition of autodestruction by the recognition of a 'self marker' and delivery of signal minus 1 is an ancient process which probably emerged in early metazoans.

Degree of chromatin fragmentation and frequency of nuclear pyknosis in Percoll-fractionated thymocytes of irradiated rats

The relationship between nuclear chromatin degradation to polydeoxyribonucleotides (PDN) and other features of interphase death were studied using thymocytes of normal and X-irradiated rats. Fractionation of the thymic cells in Percoll gradients was performed in order to separate dead from intact cells. The degree of radiation-induced chromatin fragmentation, as assessed by electrophoresis, was similar for PDN from all Percoll bands. Following irradiation 87-98 per cent of 'heavy' thymocytes were pyknotic and almost devoid of receptors to autologous erythrocytes thus comprising a dead cell population. A direct relationship between PDN content and nuclear pyknosis was noted throughout the gradient. The loss of autologous rosette-forming ability was directly related to other indices of interphase death. The possibility of PDN originating from pyknosis-prone cells and the capacity of radiosensitive thymocytes to form autologous rosettes are discussed.

Human autologous rosette-forming cells. V. Study of MHC control in erythrocyte-lymphocyte interaction

The role of the major histocompatibility complex (MHC) in human autorosette formation was studied. On a large series of healthy subjects who were typed for HLA antigens, we tested in blind rosette formation with 90 autologous and 295 allogeneic red blood cells (RBC). We found that the mean levels of auto- and allorosettes were similar, being significantly higher in females than in males. However, we failed to find any role for blood group antigens and any involvement of HLA antigens in the interactions between lymphocytes and RBC in rosette formation. Moreover, high or low autorosette levels were not associated with a particular HLA allele. The comparison of individual percentages of auto- and allorosettes indicated that 51% of the subjects displayed identical levels of auto- and allorosettes whereas 29% formed preferentially rosettes with auto- rather than allo-RBC and 20% exhibited lower autorosette than allorosette levels. Among the group of subjects who were better responders for autorosettes than allorosettes, we found an increased frequency of the haplotype A29, B44. Taken together these findings suggest that in contrast to the murine situation, the autorosetting phenomenon in humans is not HLA restricted.

Human autologous rosette-forming cells. III. Binding of erythrocytes from different species to the T-cell receptors for autologous red blood cells

Spontaneous rosette formation in humans is restricted to a subpopulation of the circulating T cells. We have previously shown that the interaction between lymphocytes and autologous red blood cells (auto-RBC) is not mediated by a self-recognition mechanism, since allogeneic (allo-) RBC bind to T cells through the same receptors. In this work, we have extended these observations to thymocytes. Using a mixed-rosette assay in which one type of erythrocyte was identified by FITC labeling, we have shown that almost all the thymocytes which attached auto-RBC could also fix allo-RBC. However, as for the peripheral blood lymphocytes (PBL), binding of human RBC to thymocytes occurred with varying affinities according to the erythrocyte's origin. In order to further study the specificity of the erythrocyte to lymphocyte binding in rosette formation, PBL were mixed with auto-RBC and erythrocytes of xenogeneic (xeno-) origin. Although very disparate incidences of rosettes were found according to the species from which the RBC were derived, most of the autorosetting lymphocytes also had receptors for xeno-RBC. In addition, preincubation of PBL with monoclonal antibody OKT11A (directed against the sheep RBC receptors on T cells) completely abrogated rosette formation with all the erythrocytes tested (human auto- and allo-, sheep, pig, and rabbit) except mouse RBC. Taken together these data strongly suggest that human auto- or allo-, as well as sheep or some other xeno-RBC, bind to T lymphocytes by a single receptor and that the combining sites are expressed with different densities or varying affinities depending upon the RBC's origin. Therefore, spontaneous autorosettes may represent T lymphocytes having high-affinity receptors for sheep RBC.

Lymphocytes express a diverse array of specific receptors for sulfated polysaccharides

Lymphocyte receptors for sulfated polysaccharides were detected in two ways, namely, by the ability of lymphocytes to form rosettes with sheep red blood cells (SRBC) coupled with one of fourteen different sulfated polysaccharides, and by the ability of cholate extracts of lymphocytes to hemagglutinate the same sulfated polysaccharide-coupled SRBC. It was found that murine lymphocytes lacked receptors for a number of glycosaminoglycans, such as hyaluronic acid, chondroitin-4-sulfate, chondroitin-6-sulfate, and dermatan sulfate, but reacted strongly with heparin, arteparon, and a number of sulfated polysaccharides of plant and bacterial origin. In each case receptor activity was demonstrated by rosetting and by the ability of lymphocyte lysates to strongly agglutinate sulfated polysaccharide-coupled SRBC. The receptors exhibited a high degree of diversity as evidenced by (a) only subpopulations of lymphocytes, particularly splenic B cells, expressing receptors for some of the sulfated polysaccharides and (b) hemagglutination-inhibition analyses revealing numerous subsets of receptors with different binding specificities. Receptor diversity was further highlighted by a 48% difference in the hemagglutination-inhibiton results between thymus and spleen. It is proposed that these receptors are involved in cell-cell communication and lymphocyte homing and recirculation. The likely target structures for the receptors in vivo are the heparan sulfates, a ubiquitous and structurally diverse family of sulfated glycosaminoglycans.

Autorosette formation in humans: study of the specificity of the T cell receptors for autologous erythrocytes

Spontaneous autorosette formation has been described as being restricted to a subpopulation of the circulating helper/inducer T cell subset. In order to study the specificity of the binding between human lymphocytes and autologous red blood cells (auto-RBC), we have investigated the relationship between autorosette forming cells (auto-RFC) and rosettes formed with allogeneic (allo-) or xenogeneic (xeno-) RBC. Using a mixed rosette assay in which the origin of the erythrocytes was assessed by the FITC labeling of one type of erythrocyte, we have shown that auto-RFC and allo-RFC belong to the same T cell subset, and that the T cells which rosette with auto-RBC can also bind xenogeneic (pig, sheep, rabbit) RBC, although a disparate incidence of rosettes is found depending upon the origin of the erythrocytes. Whether T lymphocytes co-expressed distinct receptors for RBC of different species was then investigated. Preincubation of lymphocytes with monoclonal antibody OKT11A (directed against the T cell receptors for sheep RBC) completely abrogated rosette formation with auto- or allo-RBC, indicating that auto- and allo-RBC interact with the lymphocytes by their receptors for sheep RBC. Therefore, the auto-RFC may represent T lymphocytes having high affinity receptors for sheep RBC.

Solubilization of a human lymphocyte factor for autorosette

With incubation at 45 degrees C, human peripheral blood lymphocytes (PBL) loose 80% of their capacity to form 1-hr autorosettes (AR). However, the addition of supernatant from heated lymphocytes (SHL) restores 93% of their rosette-forming capacity, while producing an inhibitory effect on nonincubated lymphocytes. A soluble factor present in SHL is active to a 1/5000 dilution; is absorbable on autologous red blood cells but not on sheep red blood cells; is RNase and DNase resistant and sensitive to trypsin and pronase; and acts variably on allogenic cells.

Human autologous rosette-forming cells. II. Specificity of the binding between lymphocytes and erythrocytes

The relationship between autorosettes and allorosettes was investigated using a mixed rosette assay in which the origin of the erythrocytes was assessed by the fluorescein isothiocyanate (FITC) labeling of one type of erythrocyte. The data show that auto- and allorosettes belong to the same T-cell subset: in most of the subjects, the percentages of T cells binding autologous red blood cells (auto-RBC) are equivalent to those binding allogeneic RBC (allo-RBC); the percentage of rosettes formed after the simultaneous addition of auto- and allo-RBC is similar to that of autorosettes alone or allorosettes alone; and nearly 80% of the rosetting cells bind both types of RBC as directly visualized in the mixed rosette assay. The experiments in which the lymphocytes are rosetted first with one type of RBC, and then with the other type support the finding that auto- and allo-RBC may bind to the lymphocytes through a single receptor which exhibits a varying affinity for RBC according to their origin.

Altered lymphocyte recognition repertoire during ageing. III. Changes in MHC restriction patterns in parental T lymphocytes and diminution in T suppressor function

Irradiated C57BL/6 and (C57BL/6 X C3H)F1 mice have been reconstituted with bone marrow prepared from young (2 month) or aged (24 month) C57BL/6 donors. Indirect examination of the T cell receptor for H-2d alloantigens on H-2b splenocytes of these reconstituted mice, using the suppression of the H-2b anti-H-2d response induced by (H-2b X H-2d)F1 anti-(H-2b anti-H-2d) suppressor cells, suggests that the allo-receptor repertoire derived from bone marrow of aged mice is different from that of T cells derived from young bone-marrow precursors. These observations were supported by direct evidence, from rosette formation with murine erythrocytes, for changes in the T cell receptor of these different (radiation-chimaera) sources of H-2b-T cells. Along with these subtle changes in the allo-receptor repertoire of T cells derived from bone marrow of aged mice grown in irradiated F1 hosts, there is a decrease (compared with mice reconstituted with bone marrow from young donors) in the apparent frequency of T cells recognizing antigen in association with the new MHC-restricting elements in these parent F1 chimaeras. Analysis of those cell subsets reported to be involved in the regulation of MLC responses suggests that some of the differences observed between T cell differentiation from bone-marrow stem cells of young or aged donors may in part be explained by a diminution in the production from bone marrow of aged mice of those cells important for homeostasis within the immune system.

Possible association of membrane and nuclear changes in gamma-irradiated rat thymocytes

gamma-irradiated rat thymocytes were incubated in medium containing fresh rat serum. After 6 hours in culture, an equal dose dependency was noted for nuclear pyknosis and the loss of surface receptors to autologous erythrocytes. Decreased rosette formation preceded the expression of pyknosis. A possible relation between the membrane changes and pyknosis during interphase death of the thymocytes is discussed.

The relationship between mouse thymocyte receptors for syngeneic and allogeneic erythrocytes and receptors for IgG

Mouse thymocytes lose the affinity for syngeneic erythrocytes in the rosette formation test after heating in the isotonic medium for 1 h at 45 degrees. The thymocyte receptors for syngeneic erythrocytes appear in the medium after heating. The rosetting of heated and washed thymocytes is restored after incubation with the supernatant obtained from heating in medium thymocytes. The receptors for allogeneic erythrocytes were not separated from thymocytes under the same conditions of heating and washing. The receptors for syngeneic erythrocytes separated by heating can be adsorbed on the column with IgG-Sepharose conjugate and probably are connected with the receptors for Fc portion of IgG.

The H-2dm1 mutation and Qa antigens

The effect of the H-2dm1 mutation on Qa-m2 expression was examined. The mutant strain B10.D2-H-2dm1 showed a fourfold increase in Qa-m2 expression when compared with the parental strain B10.D2. Qa-m2 molecules immunoprecipitated from B10.D2-H-2dm1, C57BL/10, and B10.D2 spleen cells were identical by two-dimensional (2-D) gel electrophoresis [isoelectric focusing (IEF) followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE]). It is likely therefore that the increased Qa-m2 expression is not due to gross structural alterations of the Qa-m2 molecule; in the present study, alternative explanations are discussed.

Automated rosetting assay for cell surface antigens and autorosetting lymphocytes

An automated procedure, using a Coulter counter, is described for enumerating rosette-forming lymphocytes in 2 rosetting systems in mice, detecting antibodies to cell surface antigens, and the interaction of autologous erythrocytes with thymocytes (autorosetting). The procedure gives results comparable with determinations of rosettes by light microscopy. The procedure not only estimates rosetting percentages, but can be used to titrate anti-lymphocyte antibodies, to detect autorosette inhibition factor in serum and to assay cell surface antigens in detergent lysates of spleen cells.

T cell idiotypes recognizing self-major histocompatibility complex molecules: H-2 specificity, allotype linkage, and expression on functional T cell populations

An anti-idiotypic serum (antiserum 5936, B. Rubin et al., J. Exp. Med. 1979. 150: 307) was used to demonstrate receptor sites for self-major histocompatibility complex (MHC) antigens on T lymphocytes. The antiserum was raised by injecting rabbits tolerant to mouse Ig with a B6 anti-CBA (anti-H2k) alloantibody. It recognized a large proportion of T cells from H-2k strains carrying the b, c, d or e allele at the Igh-1 locus, but only a few T cells from H-2k strains with Igh-1 alleles a, f and j. Allotype linkage of the 5936 idiotype was also demonstrated by segregation analysis. The antiserum did not recognize either H-2k B cells or T cells from other H-2 haplotypes despite the presence of a permissive Igh-1 allele. The 5936 idiotype was found to be associated with several different antigen specificities, indicating that it is not located on the binding site for foreign antigen. Furthermore, the 5936 antiserum inhibited the binding of soluble Ik antigens by H-2k, Igh-1b, T cells, and, in the presence of complement, eliminated T cells responding to different antigens in an I-Ak-restricted fashion. Collectively, the data indicate that the structure bearing the 5936 idiotype is a receptor for I-Ak antigens, expressed by strains carrying the I-Ak allele and a permissive allele at the Igh-1 locus. The relevance of this finding to the MHC-restricted recognition of antigens by T cells is discussed.

Anti-self receptors. V. Properties of a mouse serum factor that blocks autorosetting receptors on lymphocytes

Murine lymphocytes spontaneously bind autologous and allogeneic erythrocytes via receptors that primarily recognize self H-2L molecules on the erythrocyte surface. Normal mouse serum contains a factor, termed autorosette inhibition factor (AIF), that very effectively blocks autorosette formation. This paper describes experiments that determine the origin and nature of serum AIF. It was found that AIF lacks strain and species specificity, serum from several mammalian and non-mammalian species inhibiting the autorosetting of BALB/c thymocytes. However, mouse strains differed in the levels of AIF in their serum. Furthermore, AIF appears to directly interact with autorosetting receptors on lymphocytes as thymocytes from the BALB/c-H-2dm2 mutant strain, which lack autorosetting receptors, were unable to absorb the factor. Several lines of experimental evidence indicated that AIF is secreted by a population of short-lived, radiosensitive macrophages (or monocytes). Firstly, in vivo administration of the anti-macrophage agents carrageenan and silica profoundly depressed AIF levels in serum. Secondly, in vitro culturing of different lymphoid cells revealed that AIF is secreted by an adherent population of peritoneal cells. Thirdly, total body irradiation experiments demonstrated that AIF production is dependent upon a radiosensitive cell that is bone marrow derived. Finally, AIF was purified to homogeneity from mouse plasma and shown to be a single polypeptide chain with a molecular weight of 84,000.

Two maturation-associated mouse erythrocyte receptors of human B cells. II. Isolation and partial characterization of a B-cell lectin with specificity of R1

Trypsin treatment of chronic lymphocytic leukaemia (CLL) cells which have the capacity to rosette with mouse erythrocytes (M), the BM+ subtype, inhibits their capacity to rosette and releases a substance into the supernatant which agglutinates mouse and rat erythrocytes but not erythrocytes of five other species tested. This substance has been named immature B-cell lectin (IBL). The specificity of IBL was further demonstrated by fluorescence labelling, absorption and latex rosetting. IBL does not bind to pronase-treated M (pro M), indicating that it has the specificity of R1 as distinct from R2 which binds to a pronase-resistant ligand on M. Other evidence that IBL is associated with B-cell membrane receptors for mouse erythrocytes is as follows: (1) The amount of IBL released into the supernatant correlated with the trypsin sensitivity of M rosetting with different clones of BM+ CLL cells. (2) Only small amounts of IBL were released from non-rosetting cells (T cells and mature B cells). (3) Binding properties of IBL were inhibited by extract of M but not extract from ox erythrocytes. (4) High-titre solutions of IBL conferred the capacity to form M rosettes on certain types of non-rosetting B cells. IBL has a dual binding specificity. Its binding to M is inhibited by fetuin and mannan, while its binding to B cells is not inhibited by these substances. The relationship of IBL to other membrane lectins including fibronectin is discussed. Preliminary characterization indicates a high-molecular-weight (at least 300,000 daltons) glycoprotein which has a pronounced tendency to aggregate in solution. The relationship of IBL to stages of human B-cell maturation is discussed.

Autologous rosette-forming T cells regulate responses of T cells. Phenotypic and functional analysis of suppressor cells generated from autologous rosette-forming T cells after autologous mixed lymphocyte reactions

An average of 5--9% of human peripheral blood of T lymphocytes from rosettes with autologous erythrocytes (ARFT). This population responded only slightly against autologous and allogeneic non-T cells. In contrast, T cells that did not form rosettes with autologous erythrocytes (NRFT) proliferated to a greater degree in auto- and allogeneic mixed lymphocyte reactions (MLR) and also in reactions to trinitrophenyl (TNP) modified autologous non-T cells (TNP-auto-MLR) as compared with ARFT or unfractionated T cells. The ARFT populations could suppress the increased allogeneic (allo)MLR and TNP-auto-MLR of NRFT when the ARFT were added to the NRFT at the beginning of the cultures. Fluorescence-activated cell-sorter (FACS) analysis of these freshly obtained T cell fractions using monoclonal antibodies to subpopulations of T cells did not demonstrate any selective gain or less of T cell subsets in the ARFT and NRFT as compared with unfractionated T cells. But when each T cell fraction was cultured separately for a week in the presence of autologous non-T cells (auto-MLR) and the cells were again analyzed by fluorescence-activated cell sorter, there was an increase in OKT8-positive cells (suppressor/cytotoxic subset) only in the ARFT fraction. The above findings strongly suggest that suppressor T cells are generated from the ARFT fraction during an auto-MLR, these may then regulate the responses on NRFT.

Anti-self receptors. III. Lack of allelic exclusion and thymic epithelium dependence of H-2L-region-restricted receptors on lymphocytes

Murine thymocytes and peripheral lymphocytes bind autologous erythrocytes via H-2L-region-restricted receptors. After inhibiting autorosetting with different erythrocyte sonicates the specificity of these anti-self receptors was examined in F1 hybrid and chimaeric mice. Most F1 lymphocytes simultaneously expressed receptors against both parental haplotypes. Furthermore, analysis of lymphocytes from allogeneic and semi-allogeneic chimaeras clearly demonstrated that radioresistant elements in the recipient thymus did not modify the haplotype specificity of the receptors on donor-derived lymphocytes.

Anti-self receptors. IV. H-2-restricted receptors on thymocytes recognize carbohydrate structures on target cells

Rosetting between thymocytes and autologous erythrocytes in mediated by receptors on thymocytes that primarily recognize self H-2L molecules on erythrocytes. This paper describes preliminary attempts to chemically characterize the receptor and acceptor molecules involved in this H-2-restricted interaction. On the basis of sugar inhibition studies and the sensitivity of the receptors to protease and glycosidase treatments it appears that a protein receptor on thymocytes recognizes the carbohydrate portion of a glycoprotein on erythrocytes. Furthermore, the thymocyte receptor appears to recognize terminal D-galactose, D-mannose and sialic acid residues on a branched-chain carbohydrate structure on erythrocytes, with mouse strains of different H-2 haplotype expressing carbohydrate structures that differ in the linkage of these three terminal sugars. These findings indicate that H-2-restricted carbohydrate-protein interactions can occur between cells, a conclusion with important theoretical implications.