APOPTOSIS ACCOMPANIES A CHANGE IN THE PHENOTYPIC DISTRIBUTION AND FUNCTIONAL-CAPACITY OF MURINE BONE-MARROW B-CELLS CHRONICALLY EXPOSED TO PREDNISOLONE

Prednisolone (PD) is commonly used for the treatment of inflammation accompanying diseases such as arthritis, allergy, asthma, and autoimmunity. While it is well documented that PD induces apoptosis in immature T-cells of the mouse, the effects of PD on development of immature B-cells in normal bone marrow (BM) was not known. An implantation system was developed which chronically delivered PD at a rate of a few nanograms per milliliter of plasma to mice. Ten days of exposure to such levels of PD caused splenic and thymic atrophy, which was accompanied by a 50% decrease in the numbers of circulating lymphocytes. Flow cytometric analysis (FACS) of the effects of PD on the BM revealed a threefold decrease in the proportion of B220(+)IgM(-) pre-B-cells and immature IgM(+)IgD(-) B-cells. However, the mature IgM(+)IgD(+) cells were reasonably resistant to the effects of PD. A 25% decrease in small nucleated cells presumed to be part of the lymphocyte compartment was also noted from the scatter profiles of the marrow of PH-treated mice. These marked changes in BM composition were also accompanied by significant reductions in capacity of the BM to respond to trinitrophenylated-lipopoly-saccharide (TNP-LPS) after exposure to PD either in vivo or in vitro. Studies to ascertain whether apoptosis played a role in the decline in the number of developing B-cells of marrow exposed to PD were performed in vitro in order to reduce the possibility of phagocytosis of apoptotic cells. A recent modification of FACS cell cycle analysis, which is highly quantitative and allows rapid analysis of heterogenous tissues such as the marrow, was used to detect the apoptotic cells. After 16 hr of culture in 10(-7) M PD, approximately 40% of IgM(+) and B220(+) cells of BM resided to the left of G(0)/G(1) in a region associated with apoptotic cells previously termed the A(0) or ''hypodiploid'' region. Thus, these data indicate that chronic exposure to low levels of PD significantly altered the B-cell compartment of the murine bone marrow both in vivo and in vitro, potentially inducing apoptosis in these cells. (C) 1994 Academic Press, Inc.