Lymphoma models for B-cell activation and tolerance. II. Growth inhibition by anti-μ of WEHI-231 and the selection and properties of resistant mutants

Regulation of the growth of murine B-cell lymphomas has been used as a model for tolerance induction. The inhibition by anti-immunoglobulin reagents of the growth of WEHI-231 and several variant clones has now been studied. The parental line is exquisitely sensitive to growth inhibition by heterologous or monoclonal anti-μ or anti-K reagents and ceases to incorporate thymidine within 24-48 hr of exposure to anti-immunoglobulin reagents. Growth inhibition is initially reversible, but prolonged exposure to anti-μ results in cell death. This inhibition is specific for immunoglobulin light and heavy chains since growth is not inhibited by antibodies directed at either class I or class II histocompatibility antigens. In order to study the mechanism of growth inhibition, we have mutagenized WEHI-231 with ethylmethane sulfonate and cloned the surviving colonies in the presence of anti-μ. Such variants, which have been repeatedly recloned, are able to grow normally in the presence of anti-μ up to 100 μg/ml. These "resistant" clones, while expressing amounts of surface IgM similar to that observed on WEHI-231, do not differ markedly in their ability to cap their immunoglobulin receptors compared to the parental line but appear to have lost class II antigens. Cell cycle analysis revealed that anti-μ causes a block in the transition of WEHI-231 from G₁ to S phase. The relevance of these processes to models of B-cell tolerance induction are discussed.