Three B-cell surface molecules associating with membrane immunoglobulin

Three cell-surface molecules associated with surface Ig on murine B cells have been identified. Surface-iodinated resting B cells were lysed in digitonin or Nonidet P-40. The lysates were then examined by immunocoprecipitation with anti-Ig reagents and SDS-PAGE. By this procedure, a 73,000 MW heterodimer, composed of 35,000 and 38,000 MW disulphide-linked subunits, was found to be associated with both mIgM and mIgD. This association was detectable in the detergent digitonin, but not Nonidet P-40. As an alternative approach, resting B cell mIg was capped and internalized by anti-Ig induced mIg cross-linking. The resulting 'modulated' cells were then screened for surface reactivity with a panel of monoclonal antibodies. Most antibodies tested (anti-class I, -class II, -LFA, -FcR gamma, -FcR epsilon) reacted equally well with control and modulated B cells. With two, however, there was a significant reduction in surface representation on modulated B cells. One determinant corresponds to a previously undescribed 90,000 MW murine surface marker, and the other was a polydisperse glycoprotein recognized by the mAb J11D.