Search

SUMMARYA human monoclonal anticardiolipin autoantibody (ACA) of the IgA-k isotype, designated 185/ 12, is described. The antibody was prepared from peripheral B cells, obtained from a patient with a history of habitual abortion, by immortalization with Epstein Barr virus (EBV). The antibody displays a strong binding activity to cardiolipin and phosphatidyl i-serine. but not to phosphatidyicholine, phosphatidylinositol, ssDNA and dsDNA, It binds to cardiolipin in a concentration-related and saturable manner (Kd = 3·0 × 10−8 M). This reaction is dependent upon the presence of bovine serum, and is fully inhibited by cardiolipin vesicles. The 185/12 antibody exhibits different binding patterns to the solid-phase bound cardiolipin-serum complex and to its individual components (cardiolipin and bovine serum). The βmax of 185/12 binding to the complex (0·968 OD units) is higher than the sum of the βmax values calculated for each one of the complex components (0·352 + 0·179 = 0·531 OD units). Bovine serum as well as purified /Vglycoprotein I (β2-GPI) in suspension inhibit the binding of 185/12 to the complex. 185/12 binding capacity increases in direct relation to the rising concentration of/β2 -GPL Collectively, these data may be interpreted to suggest that 185/12 antibody, which is an IgA isotype. exhibits characteristics usually attributed only to antiphospholipid autoantibodies (APA) of the IgG isotype. that are associated with the clinical spectrum of APA syndrome (APA-S). It is, therefore, possible that autoantibodies of the IgA isotype could play a pathogenic role, which may be different from that of the IgG isotype. in the development of autoimmune phenomena.

Nonadherent Fc gamma receptors (Fc gamma R) expressing cells from SEYF-a tumors that form rosettes with sheep erythrocytes coated with IgG antibodies (EA) were isolated by Percoll density gradients. The EA-IgG rosette-forming cells were characterized by the parameters of 1) binding of IgG immune complexes; 2) binding of purified monoclonal antibodies against mouse FcR; 3) sensitivity to complement-dependent lysis mediated by syngeneic anti-SEYF-a antibodies; 4) expression of parental H-2 antigen when grown in F1 hybrids; 5) incorporation of [125I]5-iodo-2'-deoxyuridine; and 6) growth in syngeneic mice. The nonadherent EA-IgG rosette-forming cell population was found to be composed of both host lymphocytes as well as of tumor cells. Tumor-seeking lymphocytes then were removed from SEYF-a tumors by velocity sedimentation on Percoll. The remaining cell population was tumorigenic and expressed FcR, as well as tumor antigens. These tumor EA-IgG rosette-forming cells exhibited a very low rate of DNA synthesis compared with that of non-rosetting tumor cells.

Eluates of SEYF-a cells (from polyoma virus-induced sarcoma grown in A.BY mice) containing cytotoxic anti-SEYF-a antibodies mediated complement-dependent cytotoxicity of normal lymph node cells. Some lymphocytotoxicity was also mediated by sera of tumor-bearing mice, but the pattern of cytotoxicity was different from that exhibited by tumor eluates. The titer of lymphocytotoxic antibodies in the serum was lower than the titer of anti-SEYF-a antibodies, whereas eluates exhibited similar titers toward both target cells. These results indicated that tumor cells selectively absorbed the lymphocytotoxic antibodies from the serum. Tumor eluates had cytotoxic activity also against thymocytes, splenocytes, and even bone marrow cells. The strain distribution of sensitive thymocytes to the antibodies present in eluates indicated that Thy 1 was not involved. Unfractionated eluates as well as IgG fractions isolated from eluates were active.

We examined the specificity of the lg "coating" on murine tumor cells grown in vivo. Cells were treated in vitro for release of cell-bound lg from ascites tumors. Such uncoated cells showed an increased expression of tumor-associated antigens and a parallel decrease in intensity of the lg coat, but displayed no changes in the expressions of other normal membrane antigens. This was shown by a complement-dependent cytotoxicity assay and radioimmunoassay. These changes were attenuated if the tumor originated from animals that had been irradiated before tumor inoculation. No alterations were found with corresponding cells propaged in vitro and submitted to the same treatments. Our findings and others suggest tumor-specific antibodies among the lg coats detected on tumor cells grown in vivo.

A kinetic study of the disappearance of sensitizing antibody from metabolizing EL 4 cells in C57BL/6 mice revealed that this disappearance was at least partly due to the degradation of the antibody into dialyzable products. The degradation took place at 37 degrees C, but not at 4 degrees C, and occurred on or inside the cell. The process was specific inasmuch as only those IgG molecules that could bind to the cells were degraded, whereas unrelated third-party antibodies present in the culture medium remained intact. Although nonmalignant cells also have the capacity to degrade cell-bound antibodies, possibly the degradation of proteinaceous structures on antitumor effector mechanisms is, in part, responsible for decreased antitumor immunity.