Regulation of bone marrow lymphocyte production: IV. Altered kinetic steady state of lymphocyte production after chronic changes in exogenous stimuli.

A transient increase in B lymphocyte production in mouse bone marrow has previously been shown to follow a single administration of various exogenous agents. The effect of sustained changes in exogenous stimuli on the level of bone marrow B lymphocyte production has now been studied. In mice given multiple injections of sheep red blood cells (SRBC) for four weeks the production of bone marrow lymphocytes was augmented, as indicated by increased numbers of cytoplasmic mu-chain-bearing pre-B cells and of surface mu-chain-bearing B lymphocytes, as well as increased rates of pre-B cell proliferation and small lymphocyte turnover. In an attempt to reduce potential external stimuli, mice were raised on an elemental diet. When compared to conventionally reared mice, however, they showed little difference in bone marrow small lymphocyte production and an identical pre-B cell proliferation rate. In addition, the small lymphocyte production rate in the thymus was not consistently altered either in SRBC-treated mice or elemental diet-fed mice, whereas small lymphocyte renewal in the spleen showed changes reflecting those in the bone marrow. The results demonstrate that a chronic increase in exposure to extrinsic agents can produce a long-term elevation of the population size and production rate of bone marrow B lineage cells. This suggests that the level of the kinetic steady state of primary B lymphocyte production normally observed in the bone marrow may reflect the level of exposure to potential stimulants in the external environment.