Localization in membrane microdomains of the Ig-α/β component of the BCR expressed by a B lymphoma variant

The B cell antigen receptor (BCR) composed of the ligand-binding membrane IgM (mIgM) and the signaling component, Ig-α/β, is known to inducibly associate with membrane microdomains rich in cholesterol and sphingolipids, termed lipid rafts. In this study we tested whether the Ig-α/β portion of the BCR has targeting information that allows it to be localized in lipid rafts. In order to do this, we cross-linked the Ig-α/β on the cell surface of the variant B cell line, WEHI 303.1.5, a derivative of the immature murine B cell line WEHI 231 that lacks μ heavy chain and expresses the Ig-α/β on the cell surface by itself. Using two methods to isolate detergent-insoluble, lipid raft-like fractions, we found that Ig-α/β without accompanying mIgM was constitutively located in these raft-like fractions and that the amount was marginally increased after Ig-α/β cross-linking. These results suggest that the Ig-α/β portion of the BCR has the ability to be compartmentalized into raft-like membrane domains even when not associated with mIgM and perhaps this targeting information is normally regulated by the presence of the mIgM portion of the receptor.