The Effect of Glucocorticoids on Mitogen-Stimulated B-Lymphocytes: Thymidine Incorporation and Antibody Secretion*

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Abstract
The effects of glucocorticoids on lipopolysaccharide (LPS)-stimulated lymphocytes undergoing proliferation and differentiation were studied using cells from a corticosensitive species, the mouse, and a relatively corticoresistant species, the guinea pig. A B-cell-specific mitogen, LPS, caused a 5-fold increase in [3H]thymidine ([3H]TdR) incorporation in murine splenic lymphocytes compared to that in nonmitogen-stimulated cells. Increasing concentrations of various glucocorticoids decreased [3H]TdR incorporation. The order of biological effectiveness of the glucocorticoids was triamcinolone acetonide > dexamethasone > cortisol = corticosterone > estradiol. Triamcinolone acetonide (TA) caused decreases in [3H]TdR incorporation ranging from 24% at 10-13 M to 75% at 10-5 M. Neither cortexolone nor progesterone alone affected [3H]TdR incorporation in LPS-stimulated murine cells, but these antiglucocorticoids at a 1000-fold excess blocked the inhibitory effect of TA on [3H]TdR incorporation. Nonmitogen-stimulated murine splenic lymphocytes were also sensitive to glucocorticoids, with the same order of biological effectiveness. In contrast to the murine cells, LPS-stimulated guinea pig lymphocytes were only affected at relatively high concentrations of glucocorticoids (10-7-10-5 M), as determined by decreased [3H]TdR incorporation. When [3H]TdR incorporation was measured with time after the addition of 10-7 M TA, normal guinea pig lymphocytes were inhibited by TA, whereas leukemic guinea pig B-cells (L2C) were unaffected. The effects of glucocorticoids in vitro on LPS-induced, immunoglobulin- secreting murine B-cells were also studied. LPS caused a 5-fold increase in plaque-forming cells (PFC) at 4 days in murine spleen cell populations, and this response was unaffected by 10-13-10-9 M TA. However, 10-7 and 10-5 M TA reduced the PFC per culture by 35% and 41%, respectively. Since the number of viable cells decreased with increasing concentrations of TA, the ratio of PFC to viable cells increased with the addition of increasing concentrations of TA. We concluded that precursor B-cells induced by LPS to secrete immunoglobulin are relatively less sensitive to glucocorticoids than mitogen-stimulated B-cell populations in general.