Polyreactive binding of antibodies generated by polyclonal B cell activation. I. Polyreactivity could be caused by differential glycosylation of immunoglobulins.

Abstract

The aim of this study was to gain knowledge of the pre-immune repertoire with reactivity directed to the carbohydrate antigen dextran B512 (Dx). Polyclonal activation of spleen cells in mice has been estimated to be a method of revealing the available repertoire. Hybridoma cell lines derived from lipopolysaccharide (LPS)-stimulated C57BL/6 spleen cells were screened for reactivity with Dx and with the non-related protein bovine serum albumin (BSA). Despite the lack of structural similarity between Dx and BSA we observed that nearly all of the Dx positive monoclonal antibodies (MoAbs) cross-reacted with BSA. The Dx and BSA crossreactive MoAbs were also found to bind to several foreign-and auto-antigens, and therefore we concluded that these MoAbs fulfilled the criteria of polyreactivity. The Dx and BSA cross-reactive antibodies were produced in an apparently random fashion as judged by the use of kappa and lambda light chains and the use of V(H) J558 subfamily genes. There are two possible explanations for this type of polyreactivity: (1) LPS induces a randomly generated polyreactive and a randomly generated specific immunoglobulin (Ig) repertoire; (2) polyreactivity can be the result of post-translational modifications. Since immunoglobulins are glycoproteins we considered the possibility that post-translational modifications such as glycosylation could be responsible for the generation of the polyreactive pool. Dextran-specific and Dx/BSA cross-reactive MoAbs showed different degrees of sensitivity to inhibition of glycosylation performed by treatment with tunicamycin (Tm), an inhibitor of the formation of N-glycosidic linkages. Other polyreactive, connective and specific MoAbs were also tested. The authors found that Tm treatment had a more profound effect in reducing the binding capacity of the polyreactive antibodies (Abs), suggesting that the polyreactive Abs may be more dependent than the specific Abs on the carbohydrate content of the molecule for binding to the antigens. The authors propose that lymphocytes may use differential glycosylation as a means to generate polyreactive or monospecific Abs.