Autosensitization in vitro

Common Neurodegeneration-Associated Proteins Are Physiologically Expressed by Human B Lymphocytes and Are Interconnected via the Inflammation/Autophagy-Related Proteins TRAF6 and SQSTM1

There is circumstantial evidence that, under neurodegenerative conditions, peptides deriving from aggregated or misfolded specific proteins elicit adaptive immune responses. On another hand, several genes involved in familial forms of neurodegenerative diseases exert key innate immune functions. However, whether or not such observations are causally linked remains unknown. To start addressing this issue, we followed a systems biology strategy based on the mining of large proteomics and immunopeptidomics databases. First, we retrieved the expression patterns of common neurodegeneration-associated proteins in two professional antigen-presenting cells, namely B lymphocytes and dendritic cells. Surprisingly, we found that under physiological conditions, numerous neurodegeneration-associated proteins are abundantly expressed by human B lymphocytes. A survey of the human proteome allowed us to map a unique protein-protein interaction network linking common neurodegeneration-associated proteins and their first shell interactors in human B lymphocytes. Interestingly, network connectivity analysis identified two major hubs that both relate with inflammation and autophagy, namely TRAF6 (TNF Receptor Associated Factor 6) and SQSTM1 (Sequestosome-1). Moreover, the mapped network in B lymphocytes comprised two additional hub proteins involved in both inflammation and autoimmunity: HSPA8 (Heat Shock Protein Family A Member 8 also known as HSC70) and HSP90AA1 (Heat Shock Protein 90 Alpha Family Class A Member 1). Based on these results, we then explored the Immune Epitope Database "IEDB-AR" and actually found that a large share of neurodegeneration-associated proteins were previously reported to provide endogenous MHC class II-binding peptides in human B lymphocytes. Of note, peptides deriving from amyloid beta A4 protein, sequestosome-1 or profilin-1 were reported to bind multiple allele-specific MHC class II molecules. In contrast, peptides deriving from microtubule-associated protein tau, presenilin 2 and serine/threonine-protein kinase TBK1 were exclusively reported to bind MHC molecules encoded by the HLA-DRB1 1501 allele, a recently-identified susceptibility gene for late onset Alzheimer's disease. Finally, we observed that the whole list of proteins reported to provide endogenous MHC class II-binding peptides in human B lymphocytes is specifically enriched in neurodegeneration-associated proteins. Overall, our work indicates that immunization against neurodegeneration-associated proteins might be a physiological process which is shaped, at least in part, by B lymphocytes.

Self-tolerance for erythrocytes is not maintained by clonal deletion of T helper cells

Recent findings suggest that T helper cells specific for autologous erythrocytes are not deleted from the repertoire of the normal animal. Here, Craig Hooper proposes that tolerance of normal erythrocytes is achieved partly by conventional immunoregulation and partly by a novel process which normally prevents priming with autoantigens in vivo. The nature of the initial contact with antigen may determine which mechanism has the primary role.

Specific helper T cell reactivity against autologous erythrocytes implies that self tolerance need not depend on clonal deletion

Using a culture system which supports primary T cell proliferative responses to various antigens we have detected mouse red blood cell (RBC)-reactive T cells in lymphoid tissues from untreated mice. The release of significant amounts of interleukin 2 (IL2) indicates that T helper (or helper/inducer) cells are activated by stimulation with RBC. Upon restimulation in vitro these cells proliferate specifically against mouse RBC with the kinetics and magnitude characteristic of a secondary response. Since autologous RBC are tolerated in vivo in spite of the presence of such specifically reactive T helper cells, these findings imply that self tolerance, even to certain nonsequestered antigens, may depend largely on regulatory mechanisms rather than on clonal deletion or inactivation.

Functional role in self reactivity for Ia antigens on murine synovial cells

Cultures of synovial cells from normal CBA mice were established after collagenase treatment of synovial tissue collected from the knee joint. Morphological studies using light and electron microscopy have shown that confluent monolayers are composed of 90% triangular or stellate dendritic cells with numerous microvilli and 5% secreting cells containing many dense granules. Less than 5% contaminating cells, such as fibroblasts or macrophages, are present. The class I and class II antigens of the major histocompatibility complex, detected by indirect immunofluorescence or complement-dependent cytotoxicity, are expressed on the cell surface of normal CBA synovial monolayers. Functional Ia antigens borne by synoviocytes are evidenced by the proliferative responses they elicit from syngeneic (or allogeneic) spleen cells after a 3-day co-culture. Similarly, monolayers of Ia+ synovial cells were obtained from both MRL/lpr mice, which spontaneously develop an autoimmune syndrome, and the control MRL/n mice. Spleen cells from young MRL/lpr exhibited significantly higher levels of blastogenesis in syngeneic co-cultures than those from MRL/n mice. Conversely, with advancing age the syngeneic proliferative responses declined minimally for MRL/lpr mice and were unchanged for MRL/n mice. These findings suggest that Ia+ synovial cells can effectively interact with syngeneic lymphocytes and may initiate autoimmune reactivity.

An immunochemical analysis of a myelin basic protein serum factor: cross reactivity with residues 69-71 of the rabbit encephalitogenic sequence 65-74 of myelin basic protein

A partially purified myelin basic protein serum factor (MBP-SF), cross-reactive with residues 65-74 (TTHYGSLPQK) of myelin basic protein, has been employed in an immunochemical study to identify the nature of the cross-reacting determinant more precisely. To probe the structural requirements of this determinant, Scatchard inhibition analyses and competitive peptide inhibition radioimmunoassays were employed with a series of peptide analogs of the 65-74 region and with three different reagent antisera: a rabbit anti-rat myelin antiserum (#My05) and two antisera, one rabbit (#162) and one chicken (#66), raised against synthetic peptide S24 (TTHYGSLPQKG). Scatchard inhibition analyses with MBP-SF revealed specific inhibition of binding of 125I-S24 to #162 and #My05, but not to #66. Further delineation of the structural requirements of the cross-reactive determinant, employing a liquid-phase radioimmunoassay, revealed a unique reactivity pattern for the chicken anti-S24 antiserum which, unlike #162 and #My05, did not cross-react under high-affinity conditions with synthetic peptide S20 (GSLPQK, representing the C-terminal half of S24). This, in concert with the Scatchard data, is suggestive of the presence of a cross-reactive determinant centered around residues 69-71 of MBP.

Induction of suppressor T cells in culture--I. Cell-cell interactions

The present study was designed to examine the cellular requirements for the generation of the suppressor T cells induced in the presence of fetal calf serum in culture. When C57Bl/6 mouse spleen cells were cultured for 4-5 days, these precultured cells were shown in mixing experiments to suppress the generation of cytotoxic effector cells (CTL) against allogeneic P815 cells or the generation of anti-SRBC humoral response by freshly explanted C57Bl/6 spleen cells. Spleen cells cultured in the presence of silica (0.5 mg) for 4 days, did not develop suppressor activity. However, when silica was added 3 days after the start of the suppressor generation culture, the development of suppressor cells was only slightly affected, although the phagocytic activity of these spleen cells was still totally abolished. When plastic or G-10 Sephadex column nonadherent spleen cells were cultured alone for 4-5 days, these cells did not suppress the generation of CTL or anti-SRBC humoral response. When the nonadherent spleen cells were cultured with plastic adherent spleen cells, however, suppressor cells developed and the suppressor activity of these cells was dependent on the number of adherent spleen cells co-cultured with the non-adherent spleen cells. This activity of the adherent spleen cells was insensitive to treatment with anti-Thy 1.2 serum plus complement and to X-irradiation. Furthermore, adherent PEC could not substitute for adherent spleen cells, indicating a possible tissue specificity for the macrophages in the adherent cell fraction which can function in supporting and/or accelerating the differentiation of "immature" suppressor T cells. Finally, culture-induced suppressor T cells were sensitive to X-irradiation and their activity was refractory to IL2 (TCGF), whereas the activity of alloantigen-induced suppressor cells was sensitive to IL2.

Autocytotoxic cells against normal leucocytes identified in mouse mesenteric lymphnodes

Plaques were formed in monolayers of leucocytes prepared from mesenteric lymphnodes (LN) of normal mice. The plaques were first detected after 2 h incubation, followed by a sudden increase in number at 7 h, and reached a peak between 11 and 21 h. Large cells were observed in almost all plaques under the microscope. The large cells attached surrounding leucocytes via cytoplasmic extensions, and held aggregated leucocytes on their cell surface. Aggregated leucocytes were lyzed and/or phagocytized by the large cells. Results suggest that plaque formation was due to the direct, indiscriminate killing of normal leucocytes by the large cells. The large cells increased with age. The large cells were contained in the adherent cell fraction but not the non-adherent fraction, and were removed from leucocytes by the carbonyl iron method. Thus, the large effector cells may be related to macrophages.

Generation of autologous mixed leucocyte reactions during the course of infection with Theileria parva (East Coast Fever) in cattle

During the course of East Coast Fever (ECF) in cattle, an examination was made of the evolution of autologous mixed leucocyte reactions (MLR) between normal responder lymphocytes collected prior to infection and stimulators cells prepared from infected lymphoid organs at intervals after challenge. Proliferative responses were induced by spleen cells, peripheral blood leucocytes (PBL) and cells (LNC) from both regional and distant lymph nodes. The proliferation by normal PBL in response to LNC occurred earlier in the course of infection and was of greater magnitude than the MLRs induced by spleen cells and PBL. The ability of LNC to stimulate an autologous MLR declined after 14 days post-challenge, whereas both spleen cells and PBL were stimulatory for normal PBL until the death of the host at 18--20 days after challenge. The results imply that the earliest stimulation to the lymphocyes involved in cell-mediated immunity is afforded in the absence of detectable macroschizonts (less than 0 . 1 %). The inductive signal(s) probably emanates from transformational or parasite-coded antigens on blast cells which first appear around 8--10 days after infection. The continual generation of infected lymphoblasts may initiate proliferation of additional leucocytes involved in cell-mediated immunity at later intervals during the course of infection. The capacity of the host to mount humoral and cell-mediated responses to the infected cells is late in relation to the pathogenesis and outcome of the infection.

Susceptibility of adherent versus suspension target cells derived from adherent tissue culture lines to cell-mediated cytotoxicity in rapid 51Cr-release assays

Preparation of target cells from tissue culture lines which grow adherent to tissue culture vessels is often desirable for tests of cell-mediated cytotoxicity (CMC). In the present study we used cells derived from adherent tissue culture lines to compare the merits of suspension vs. adherent target cells in short-term 51Cr-release assays. Cytotoxic activity of murine spleen cells sensitized in vitro against allogeneic spleen cells or syngeneic sarcoma cells was tested with fibroblast or sarcoma target cells. In parallel tests, aliquots of tissue culture lines were detached and used as either suspension or adherent target cells in CMC assays, matching the concentrations of suspension and adherent target cells. In both allogeneic and syngeneic combinations adherent target cells released less 51Cr spontaneously and were more susceptible to CMC than their suspension counterparts.

Studies on induction and control of cell-mediated autoimmunity. I. Induction of "autoreactive" T lymphocytes in mice by cyclophosphamide

Injection of a single dose of cyclophosphamide (CY) (125 mg/kg) or a combination of a small dose of CY (20 mg/kg) and 2.5 mg/kg lipopolysaccharide induces a transient appearance of autoreactive T lymphocytes (T-ARC) in the spleens of mice. The T-ARC activity reaches a peak 6 days after CY injection and could not be detected 8 days after this treatment. For testing T-ARC activity, spleen cells were injected into the footpads of syngeneic recipients, and the resulting lymph node enlargement at the draining site of cell inoculation and the content of nucleated cells in the lymph node was determined. Possible explanations of this autoimmune phenomenon are discussed. It is postulated that CY-resistant precursors of T-ARC are stimulated by "new" antigenic sites present on the surface of B lymphoblasts repopulating the CY-damaged spleen in a period of transient absence of CY-sensitive suppressor cells.

Proliferative reactivity of T cells to autologous, cell-associated antigens

T cells capable of proliferating in response to signals from autologous cells can be demonstrated in normal peripheral blood. The stimulating cell is contained among populations enriched in B cells, "null" cells, and monocytes, but not among populations enriched in T cells. Density gradient fractionation indicated that the autologous reactive T cell may represent a subpopulation of cells responsive in allogeneic mixed lymphocyte cultures. This was confirmed by negative selection (BUDR and light) experiments which also indicated that the "autologous" stimulus can be mediated by at least some allogeneic cells. In a portion of patients with active systemic lupus erythematosus, autologous reactivity was reversibly blocked. Prior incubation of either responding T or stimulator cells at 37 degrees C restored this reactivity.

In vitro induction of tumour-specific immunity V. Detection of common antigenic determinatnts of murine fibrosarcomas

Two 3-methylcholanthrene and a spontaneous BALB/c fibrosarcoma were examined for tumour-associated antigens (TAA) by in vivo and in vitro induction of tumour-immune responses. When BALB/c mice were immunized to these fibrosarcomas by surgical tumour removal, cross-reacting tumour-associated transplantation antigens (TATA) were detected on all 3 tumours. Cytotoxic effector cells (CL) were then induced in vitro by co-culture of BALB/c spleen cells with the spontaneous, or one of the carcinogen-induced fibrosarcomas. These CL were shown to be cytotoxic T cells (Tc) and to be directed against cross-reacting TAA on all 3 tumours, by two in vitro 51Cr-release assay systems, direct 51Cr-release cytotoxicity and cellular competitive inhibition of 51Cr release. Further studies demonstrated that the fibrosarcoma TAA involved in in vitro induction of Tc were not present on normal adult or foetal tissues. A secondary cytotoxic response was also detected in vitro when spleen cells from mice immunized to a carcinogen-induced fibrosarcoma were tested. The patterns of cross-reactivity detected by the in vivo and primary in vitro tumour-immune responses suggested that the TAA detected in vivo (TATA) were not identical to the TAA detected in vitro.

Immunological T-cell memory in the in vitro-induced experimental autoimmune orchitis: specificity of the reaction and tissue distribution of the autoantigens

Immunological memory has been induced in vitro against testicular autoantigens by priming normal rat T lymphocytes against autologous testis cells, and by permitting the isolated blast cells to revert back to small secondary lymphocytes (secondary EAO cells) in the absence of the priming antigen. The secondary EAO cells vigorously respond in a secondary response when reconfronted with syngeneic testis or lymphoid cells. Their responsiveness to nonself stimulator cells is, however, reduced. Secondary cells derived from concanavalin A-stimulated blasts, do not show that pattern of specificity. The specificity of the secondary EAO cells is definite, and cannot be affected by further culture on allogeneic fibroblasts, which are antigenic for unprimed T lymphocytes. At least part of the autoantigens are determined by the major histocompatibility gene complex (MHC). Factors provided by the culture system do not appear to determine the specificity of this reaction. Only minor cell populations can restimulate secondary EAO cells. One of these populations is presumably phage-like cells within the lymphoid populations can elicit a secondary EAO response. Thus, the autoantigens relevant in the secondary EAO response are either MHC antigens restricted to these testicular and lymphoid subpopulations, or MHC antigens recognized in conjunction with organ-specific non-MHC determinants.

Identification of a subpopulation of lymphocytes in human peripheral blood cytotoxic to autologous fibroblasts

A naturally occurring subpopulation of human peripheral blood lymphocytes is cytotoxic to autologous and/or allogeneic fibroblasts. The autocytotoxic lymphocytes have a receptor for the third component of complement and for aggregated gamma globulin, do not form rosettes with sheep red blood cells, and are not removed by passage through nylon. The autocytotoxic subpopulation is not present in the thymus and tonsils of normal children or in the peripheral blood of individuals with X-linked agammaglobulinemia. Fibroblast absorption experiments demonstrate that the autocytotoxic cells are "sensitized" to antigens expressed on allogeneic fibroblasts in addition to the antigens expressed on autologous cells. Some normal individuals have a second subpopulation of lymphocytes that may "regulate" the autocytotoxic cells. The relevance of these observations to the murine autocytotoxic cells is discussed.

Lymphocyte transformation induced by autologous cells. IV. Human T-lymphocyte proliferation induced by autologous or allogeneic non-T lymphocytes

An autologous mixed lymphocyte reaction was demonstrated between T and non-T lymphocytes. Sheep erythrocyte rosetting was used to separate human lymphocytes into T and non-T lymphoid preparations. Non-T lymphocytes stimulated the proliferation of autologous T lymphocytes. The cell in this preparation that was most stimulatory had the characteristics of a K lymphocyte. The allogeneic mixed lymphocyte reaction was also shown to reflect the proliferation of T lymphocytes stimulated by allogeneic non-T lymphocytes. Proliferation of T lymphocytes in the allogeneic mixed lymphocyte culture probably reflects a response to both foreign histocompatibility determinants and determinants present on non-T lymphocytes. It is suggested that the proliferative response of T lymphocytes to autologous non-T lymphocytes may be a step in the process by which T lymphocytes regulate immunity.

Coexistence in human sera of a cell (membrane?) ANTIGEN AND Of autoantibodies directed against it

Antibodies purified from sera of patients with Burkitt's lymphoma by absorption onto and elution from cultured lymphoblastoid cells, were labeled with 125I and repurified by repeating the absorption-elution procedure. The doubly purified antibodies could bound with a high degree of efficiency to immunoadsorbents prepared by entrapping in polyacrylamide gel normal human serum or exudate fluids from patients with ovarian or breast cancer. Binding was specific, as it could be inhibited by high dilutions of human sera but not by animal sera. Globulin fractions of human sera were strongly inhibitory. Their capacity to inhibit was lost after treatment with rabbit anti-human IgG serum, indicating that at least part of the inhibition could be ascribed to antibodies. Some inhibitory activity was also found, however, in the "albumin" fractions of sera, suggesting that an antigen was also involved. It appears, therefore, that practically all human sera contain antibodies reacting with an antigen(s) which is present on human cells and is also circulating freely in serum and other body fluids. Sera of patients with Burkitt's lymphoma contained, on the average higher concentrations of these antibodies, as compared to sera of individuals not suffering from this disease. This antigen is thought to be associated with the cell membrane and has been identified in cells of widely differing origin.

Immunosuppression by fetal liver as a model for tolerance to self

The embryonic liver chimera system was used as a model to study the development of tolerance to self antigens. It was found that the permanent tolerant state which was induced in (C3H/eb x C57BL/6)F1 irradiated hosts following reconstitution with parental C57BL liver cells could be due to the development of suppressor cells within the liver cell inoculum, which specifically prevent reactivity of immunocompetent cells. General suppressor activity could be found in embryonic liver cells at early stages of gestation. However, the differentiation of such cells into specific suppressor of "self" antigens is dependent on the presence of the thymus.

The role of thymus on autosensitization against syngeneic normal and malignant cells

Mouse lymphocytes were exposed to syngeneic fibroblasts and tumor cells in Millipore chambers inserted into the peritoneal cavity of intact and thymectomized mice. Autosensitization to fibroblasts occurred only if the chambers were carried by thymectomized mice. Sensitization to tumor-specific antigens also took place in intact mice. If thymic extract was administered to thymectomized mice autosensitization in the chambers was inhibited.

Significance of spontaneous autorosettes in rats

Between 10(3) and 10(4) auto-rosette-forming cells (RFC) per 10(6) lymphocytes are observed in lymphoid organs of normal rats in vitro. Counts are significantly higher in the thymus than in other organs. Contrary to what has been previously described in mice, auto-RFC are not inhibited by fresh normal rat serum. The data presented are compatible with the hypothesis that auto-RFC differ from the lymphocytes which recognize only alloerythrocytes according to histocompatibility differences. There is evidence which suggests that autorosette formation is linked to the expression of new determinants on ageing erythrocyte membranes.

In vitro "education" on autologous human sarcoma generates non-specific killer cells

The cytotoxic effects mediated by lymphocytes from cancer patients after in vitro "education" on autologous tumor cells have been investigated. Peripheral blood lymphocytes from three sarcoma patients were cultivated on autologous tumor-cell monolayers and tested thereafter in a micro-cytotoxicity assay against tumor and fibroblast cells. This procedure led to the progeny of non-specific killer cells. As the phenomenon did not occur when the same lymphocytes were co-cultivated with autologous fibroblasts, the generation of non-specific effector cells may have been caused by specific antigenic triggering. The presence of autologous serum during "education" was found to inhibit the manifestation and/or the generation of killer cells. The same serum was without effect when added during the cytotoxicity assay only.