Lymphocyte population kinetics during the development of the immune system. B cell persistence and life-span can be determined by the host environment.

We have investigated the kinetic behaviour of LPS reactive B cells during the development of the immune system. By studying the persistence of LPS reactive spleen cells transferred from adult C57BL/6 donor mice into histocompatible C57BL/10 Sc.Cr LPS non-responder mice we have confirmed that B cell populations obtained from adult donor mice decay rapidly after transfer into adult recipients. In contrast, the same cell populations after transfer into neonatal recipients are able to divide and maintain their numbers for approximately 2-5 weeks in the host's spleen. In fact, comparison of hosts at different ages show that with the increasing age of the host the fate of donor B cells evolves to mimic the behaviour observed upon transfer into adult recipients. Kinetic studies of LPS reactive spleen cells obtained from newborn (2 weeks old) C57BL/6 donors after transfer into adult C57BL/10 Sc.Cr mice have shown that young donor cells were able to keep at constant numbers in the adult environment for the first approximately 10-15 days after transfer and to decay afterwards in the host's spleen at the same rate as observed upon transfer of spleen cells from adult donors into adult hosts. These studies provide the first evidence for the different kinetic behaviour of lymphoid B cell populations in developing and mature immune systems, confirm that cell persistence correlates with cell activation and division, and show that B cell life-span is also dependent on the host environment.