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 a ccompanying diseases such as arthritis, allergy, asthma, and autoimmun ity. 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 nanog rams per milliliter of plasma to mice. Ten days of exposure to such le vels of PD caused splenic and thymic atrophy, which was accompanied by a 50% decrease in the numbers of circulating lymphocytes. Flow cytome tric analysis (FACS) of the effects of PD on the BM revealed a threefo ld decrease in the proportion of B220(+)IgM(-) pre-B-cells and immatur e IgM(+)IgD(-) B-cells. However, the mature IgM(+)IgD(+) cells were re asonably resistant to the effects of PD. A 25% decrease in small nucle ated cells presumed to be part of the lymphocyte compartment was also noted from the scatter profiles of the marrow of PH-treated mice. Thes e marked changes in BM composition were also accompanied by significan t reductions in capacity of the BM to respond to trinitrophenylated-li popoly-saccharide (TNP-LPS) after exposure to PD either in vivo or in vitro. Studies to ascertain whether apoptosis played a role in the dec line 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 heterogenou s 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 asso ciated with apoptotic cells previously termed the A(0) or ''hypodiploi d'' region. Thus, these data indicate that chronic exposure to low lev els of PD significantly altered the B-cell compartment of the murine b one marrow both in vivo and in vitro, potentially inducing apoptosis i n these cells. (C) 1994 Academic Press, Inc.