An analysis of the growth and differentiation of B cells isolated from follicles of the ileal Peyer's patch of sheep.

We developed a method to isolate and culture cells from the lymphoid follicles of the ileal Peyer's (PP) patch of young sheep (6-12 weeks). These cells were 98% sIgM+ B cells and 1% T cells. Cultured follicular cells were used to investigate B-cell proliferation and differentiation. Less than 50% of B cells were viable after 24 hr of culture and this decrease in B-cell viability also occurred following co-stimulation with pokeweed mitogen (PWM) and recombinant bovine interleukin-1 (rBoIL-1) or rBoIL-2. In contrast, co-stimulation with PWM and either rBoIL-1 or rBoIL-2 induced a marked proliferative response that was maximal on Day 4 of culture. Cytokine-induced proliferation of the B cells required PWM co-stimulation and proliferation induced by rBoIL-1 and rBoIL-2 was neither additive or synergistic. This suggests that PWM bound a molecule or molecules that signalled responsiveness to both rBoIL-1 and rBoIL-2. Culture of follicular cells with PWM and both rBoIL-1 and rBoIL-2 also resulted in B-cell differentiation. This differentiation was associated with decreased proliferation, an increased number of viable B cells, and increased expression of both surface IgM and non-Ig membrane molecules. Thus, co-stimulation of ileal PP follicular cells with PWM and rBoIL-1 and rBoIL-2 resulted in both B-cell proliferation and differentiation.