Heterogeneity of the B cell subpopulation operationally defined by (a) differentiation antigen(s) common to MOPC 104E and mature IgM plasma cells.

An antiserum raised in rabbit against MOPC 104E myeloma cells was extensively absorbed by murine IgM, thymocytes and spleen cells. Using indirect immunofluorescence, the distribution of the corresponding mouse plasma cell antigen(s) (MPCA) was determined among immunized spleen cells. Only 1-3% of the cells were stained but this MPCA-bearing subpopulation included all IgM plasma cells, a sizable proportion of IgG plasma cells and about one third of the antigen binding cells identified following deliberate immunization. It is therefore proposed that MPCA is transiently expressed during the antigen-induced differentiation of virgin B lymphocytes into memory cells as it does during the maturation process into Ig-producing cells and thus reflects the ontogenic relationship of these two differentiation pathways.