Bm5 B cell A memory B cell arising in the germinal center that is IgD-negative and has undergone somatic mutation of the variable region of the immunoglobulin heavy and light chain genes. Bm5 B cells are also reportedly CD10-positive, CD23-negative, CD38-negative, CD39-positive, CD44-positive, CD71-positive, and CD77-negative. Bm5 B lymphocyte Bm5 B-cell Bm5 B-lymphocyte cell IgD-negative memory B cell