AbstractThe B cell mitogens lipopolysaccharide (LPS), purified protein derivative of tuberculin (PPD) and fetal calf serum (FCS) all stimulate spleen cells from nude mice to increased DNA‐synthesis 14 to 16 h after the initiation of mitogenic stimulation. The three mitogens also induce the maturation of B cells to plaque‐forming cells (PFC). All three mitogens stimulate largely identical B cell populations. The extent to which B cells are stimulated to DNA synthesis and to the development of PFC varies from mitogen to mitogen.PFC arise by clonal growth through proliferation and maturation. A “hot pulse” of radioactive thymidine given between 0 and 20 h of stimulation has no effect on the development of PFC during subsequent mitogenic stimulation. Pulses given between 24 and 36 h after stimulation abolish the development of over 90 of the PFC. The minimum pulse time required for maximum inhibition of the development of PFC during that time is 6 h. Beyond 36 h of stimulation by either of the three mitogens, PFC emerge rapidly. Between 60 and 72 h less than 10 of all PFC emerging at 72 h are abolished by a “hot pulse”.The kinetics of the clonal development of PFC after mitogenic stimulation are compared to that of antigenic stimulation. The comparison suggests that B cells stimulated by antigen in thein vivoprimary immune response culture system go through a longer period of proliferation than when they are stimulated by mitogen before matura
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