Expression of the Fc gamma receptor on Ly-1+ B lymphocytes.

The expression of IgG Fc receptor (FcR) molecules was examined on Ly-1+ B cells and B cells tumors. FcR molecules were found on a representative Ly-1+ B cell lymphoma of the pre-B and as well as of the mature cell B phenotypes. The expression of the FcR did not change on these cells during their differentiation to B cells or to antibody-secreting cells, respectively. Ly-1+ B cells were found at low frequency (approximately 2%) in the spleens of normal mice, and in the peritoneal cavity where their representation was greater. The frequency of Ly-1+ B cells declined after birth, although their numbers increased in both organs. These Ly-1+ B cells expressed the FcR molecule throughout ontogeny. Furthermore, the amount of FcR expressed on Ly-1+ B cells was similar to the levels expressed on their "conventional" (Ly-1-) B cell counterparts. The FcR was also found on Ly-1+ B cells from autoimmune mice. The significance of the expression of FcR molecules on Ly-1+ B cells is discussed.