Receptors for IgM on murine lymphoid cells.

Murine lymphoid cells from the thymus, lymph node and spleen were shown by indirect immunofluorescence, to bear membrane receptors for purified IgM of human origin. The bond between IgM and the cells took place through the Fc re gion, as demonstrated with isolated fragments of the normal IgM molecule. Two distinct myeloma IgM lacked this biological activity. The cytophilic origin of part of the immunoglobulin usually described on T-cell membranes is discussed.