Reduced responsiveness of immature B cells to the B cell mitogen, lipoprotein.

When pre-B cells are isolated from bone marrow and incubated in vitro for several days, they spontaneously differentiate into LPS-reactive B cells. These newly produced B cells do not respond to another B cell mitogen, lipoprotein (Lp). The lack of Lp reactivity of newly produced B cells represents a qualitative difference between these cells and B cells in peripheral tissues that respond equally well to both LPS and Lp. Thus, responsiveness to different mitogens provides unique markers to identify B cells at early stages of development.