B cell growth factor activity in supernatants of MRL-lpr/lpr derived T cell hybridomas.

The aim of this study was to characterize B cell growth factor (BCGF) activity derived from autoimmune MLR-lpr/lpr cells. In order to obtain supernatants containing BCGF that are free of suppressor lymphokines, MLR-lpr/lpr spleen cells were fused with BW 5147 thymoma cells to form T cell hybridomas. High fusion frequencies were obtained without prestimulation in vitro indicating a high degree of preactivation in vivo. Nineteen of 172 of the resulting hybridomas produced a B cell growth factor, which induced proliferation of small B cells when co-cultured with low doses of an anti-mu antibody. Maximal augmentation of B cell proliferation by supernatants containing BCGF required low cell concentrations and the presence of factor during the initiation of the culture. These data indicate that one of the possible active components of the supernatants containing BCGF is the recently characterized lymphokine interleukin 4 (IL-4).