Effect of anti-carrier antibody on carrier-determined tolerance

The distribution of heterophilic antigens and their relationship with autoimmune diseases

Introduction

Microbial infections are associated with the occurrence of autoimmune diseases, but the mechanisms of microbial infection inducing autoimmune diseases are not fully understood. The existence of heterophilic antigens between microorganisms and human tissues may explain part of the pathogenesis of autoimmune diseases. Here, we investigate the distribution of heterophilic antigens and its relationship with autoimmune diseases.

Methods

Monoclonal antibodies against a variety of microorganisms were prepared. The titer, subclass and reactivity of antibodies with microorganisms were identified, and heterophilic antibodies that cross-reacted with human tissues were screened by human tissue microarray. The reactivity of these heterophilic antibodies with different individuals and different species was further examined by immunohistochemistry.

Results

In this study, 21 strains of heterophilic antibodies were screened. The results showed that these heterophilic antibodies were produced due to the existence of heterophilic antigens between microorganism and human body and the distribution of heterophilic antigens had individual, tissue and species differences.

Conclusion

Our study showed that heterophilic antigens exist widely between microorganisms and human body, and the heterophilic antigens carried by microorganisms may break the immune tolerance of the body through carrier effect and initiate immune response, which may be one of the important mechanisms of infection inducing autoimmune diseases.

Isolation and characterization of six monoclonal antibodies raised against human RAD51 recombinant protein

Monoclonal antibodies were produced against recombinant human RAD51 recombination protein. The antibodies of IgG subclasses were isolated from serum-free cell culture medium and purified by affinity chromatography on protein A-Sepharose. The antibodies can be used to detect specifically RAD51 protein on immunoblots of total cell lysates. Native RAD51 protein is specifically precipitated from lysates of human cells. In addition, these antibodies readily detect RAD51 in the cell nucleus by immunofluorescence staining. Epitope mapping on overlapping peptides spanning the complete primary amino acid sequence of human RAD51 revealed that three monoclonals recognize an epitope on RAD51 very close to the N-terminus of the protein (amino acids 16 to 20); the other three monoclonals interact with amino acids 85 to 95 of human RAD51.

Antigen-independent activation of T cells mediated by a novel cell surface heterodimer (Tp135-145)

A new heterodimeric structure, Tp135-145, which can mediate interleukin 2 (IL2) production and Ca2+ mobilization by Jurkat cells is described. This structure was identified by a monoclonal antibody, MX24, on the surface of either T3/TcR+ or T3/TcR- human T cell lines as well as on B cell lines. Biochemical studies showed that antibody MX24 precipitated two polypeptide chains of 135 and 145 kDa, respectively, in lysates from 125I-labeled T cells. After reduction the 135-kDa polypeptide chain shifted to 140 kDa, whereas the molecular mass of the other polypeptide remained unchanged. The apparent molecular masses of the desialylated polypeptides differed by 5 kDa. No common peptide fragments between the two polypeptide chains were found after limited proteolysis by Staphylococcus aureus V8 protease. The expression of Tp135-145 was independent of the expression of the T3/TcR molecular complex. Incubation of Jurkat cells with anti-TcR or anti-T3 monoclonal antibody induced complete modulation only of the T3/TcR complex but not of Tp135-145. Conversely complete modulation of Tp135-145 was observed after incubation of these cells with MX24 antibody. Functional studies showed that anti-Tp135-145 antibody MX24 induced high levels of IL2 production in Jurkat cells. In addition, incubation of these cells with MX24 resulted in Ca2+ mobilization from internal stores. In peripheral blood, Tp135-145 was found to be expressed by 39%-76% of resting T cells in individual donors. Two-color flow microfluorimetry showed that the Tp135-145+ cells were equally distributed on the CD4+ and CD8+ subsets. Incubation of peripheral blood T cells with antibody MX24 resulted in IL2 production and cell proliferation. Taken together these results suggest that Tp135-145 is a novel surface molecule involved in antigen-independent pathway of T cell activation.

Identification of a novel 45-kDa cell surface molecule involved in activation of the human Jurkat T cell line

This report describes a surface molecule, Tp45, which appears to be involved in interleukin 2 production and Ca2+ mobilization by Jurkat cells. The Tp45 molecule was identified by a monoclonal antibody, MX13, on the surface of either T3/TCR+ or T3/TCR- human T cell lines. Biochemical data showed that mAb MX13 precipitated a single polypeptide chain of 45 kDa both under reduced and nonreduced conditions from lysates of 125I-surface-labeled cells. Sequential immunodepletion experiments using lysates of 125I-labeled T3/TCR+ cells showed that Tp45 was distinct from the alpha chain of the TCR complex. However, incubation of such cells with either anti-T3 or anti-TCR monoclonal antibody induced complete modulation of both the T3/TCR complex and Tp45. Conversely, complete modulation of both Tp45 and the T3/TCR complex was observed after incubation with anti-Tp45 antibody. Functional studies showed that anti-Tp45 antibody induced high levels of interleukin 2 production in Jurkat cells. In addition, incubation of these cells with the antibody resulted in Ca2+ mobilization from internal stores. Anti-Tp45 antibody reacted with 3-19% peripheral blood (E-rosette-positive) T cells in individual donors. The magnitude of the proliferative response elicited by anti-Tp45 antibody for peripheral blood T cells was lower than that induced by an anti-T3 antibody. This observation is compatible with the idea that only a subpopulation of T cells is reactive with anti-Tp45. Multicolor flow cytometry analysis showed that the Tp45+ cells belong preferentially to the T8 subset.

A novel 90-kDa polypeptide (Tp90) possibly involved in an antigen-independent pathway of T cell activation

A novel surface molecule, Tp90, is described which appears to be involved in an antigen-independent pathway of human T lymphocyte activation. The Tp90 molecule was identified by a monoclonal antibody (mAb), MX20, obtained from a fusion using spleen cells of a mouse immunized with cells from two T cell leukemia lines, Jurkat and HPB-ALL. Biochemical data show that Tp90 is distinct and physically independent from the structures already known to be involved in T cell activation, namely T11, T44 or T3/TCR. These results were confirmed by antibody-induced antigen modulation experiments. Modulation of Tp90 had no effect on the expression of T3 and of the T cell receptor. Conversely, the expression of Tp90 was not affected by modulation of the T3/TCR molecular complex by either anti-T3 or anti-TCR antibody. Functional studies showed that anti-Tp90 mAb MX20 induced high levels of interleukin 2 production in Jurkat cells. Modulation of the T3/TCR complex significantly decreased the response of Jurkat cells to stimulation by antibody MX20, suggesting that the T3/TCR complex regulates the ability of the Tp90 molecule to induce IL 2 synthesis. In addition to its effect on Jurkat cells, anti-Tp90 mAb was found to be mitogenic for peripheral blood T cells. As the magnitude of the proliferative response elicited by anti-Tp90 mAb was lower than that induced by anti-T3 mAb, the possibility was considered that only a subpopulation of T cells is reactive with anti-Tp90. Indeed as determined by FACS analyses, only 3-14% of E-rosette-positive cells were stained with mAb MX20. In addition, multicolor flow cytometry analysis showed that the Tp90+ cells belong preferentially to the CD8 subset.

Detection of the common acute lymphoblastic leukemia antigen in the serum of leukemia patients

The common acute lymphoblastic leukemia antigen (CALLA) has been detected in biological fluids using a radioimmunoassay based on the inhibition of binding of 125I-labeled monoclonal anti-CALLA antibody to glutaraldehyde-fixed NALM-1 cells. With this assay, we showed first that CALLA was released in culture fluids from NALM-1 and Daudi cell lines but was absent from culture fluids from CALLA negative cell lines. Then, we found that the sera of 34 out of 42 patients (81%) with untreated common acute lymphoblastic leukemia (c-ALL) contained higher CALLA levels than any of the 42 serum samples from healthy controls. The specificity of these results was further demonstrated by testing in parallel the sera from 48 patients with CALLA negative leukemias, including 26 acute myeloid leukemia (AML), 12 T-cell acute lymphoblastic leukemia (T-ALL), and 10 acute undifferentiated leukemia (AUL). All of these sera gave negative results, except for one patient with AUL, who had a significantly elevated circulating CALLA level, and one patient with AML, who had a borderline CALLA level, 3 SD over the mean of the normal sera. Preliminary results suggest that circulating CALLA is associated with membrane fragments or vesicles, since the total CALLA antigenic activity was recovered in the pellet of the serum samples centrifuged at 100,000 g. In addition, the CALLA-positive pellets contained an enzyme considered as a membrane marker, 5'-nucleotidase. Evaluation of the clinical importance of repeated serum CALLA determinations for the monitoring of c-ALL patients deserves further investigation.