Differential activity of recombinant lymphokines on mouse B cell proliferation and cell cycle progression are revealed by 5-bromo-2'-deoxyuridine/Hoechst 33258 dye flow cytometry.

Activation of resting mouse B cells with anti-mu chain antibodies (anti-mu) leads to cell proliferation. We have investigated the effect of recombinant T cell interleukins (IL 2 to IL 6) on such anti-mu-induced proliferation. No proliferative response was detected when IL 2, IL 3 and IL 6, either alone or in combination with anti-mu, were studied. Furthermore, neither IL 4 nor IL 5 could induce proliferation when added alone to B cell cultures. However, when combined with anti-mu, IL 4 as well as IL 5 stimulated cell growth. Analysis by 5-bromo-2'-deoxyuridine/Hoechst 33258 flow cytometry revealed distinct effects of IL 4 and IL 5 on B cell growth. In the presence of anti-mu, both IL 4 and IL 5 co-stimulated unfractionated splenic B cells. However, when B cells were separated into subpopulations by density, IL 4 proved to be a cell cycle progression factor, stimulating the majority of resting B cells to enter the cell cycle. In contrast, IL 5 had little effect on the resting fraction of B cells. Rather, IL 5 acted as a co-competence factor, stimulating predominantly low-density B cells. Following exposure of anti-mu alone, most B cells accumulated in the G1 of the second cycle. Upon addition of IL 4, the cells acquired the ability to progress into the next S phase compartment. Contrary to what is seen when B cells are stimulated by other mitogens, very few cells are in the G2 compartments after anti-mu plus IL 4 stimulation. This phenomenon was not due to a differential cell cycle progression rate. Our findings provide an analytical basis for fractionating cell-cycle-compartment-specific B cells for their molecular study.