A. I.29µ+ B lymphoma cells were treated with LPS to induce differentiation towards IgM secretion. At the indicated times, cells were lysed in TritonX114 to separate soluble and integral membrane proteins (aqueous and detergent phases, respectively). Aliquots from the two phases were resolved electrophoretically and the blot was decorated by anti-µ antibodies. The blue arrow points at a band likely corresponding to µs2L2C575OX, the intensity of which increases upon LPS stimulation. 