Regulation of IL-5R expression in normal, non-Ly-1 (CD5) B cells was evaluated. Freshly isolated unfractionated spleen B cells express little or no detectable IL-5R. In contrast, B cells stimulated with anti-Ig-dextran conjugates express substantial numbers of IL-5R. Phenotypic analysis of the B cells responding to anti-Ig-dextran, and expressing IL-5R, demonstrates that these cells do not express Ly-1 or Mac-1. Scatchard analysis of B cells stimulated with anti-IgD-dextran reveals two classes of IL-5R: a high affinity receptor with a Kd of 17 pM and approximately 300 receptors/cell, and a low affinity receptor with a Kd of 0.6 nM and approximately 1000 receptors/cell. Peak receptor expression in response to anti-IgD-dextran is seen 72 h after stimulation and with a dose of 10 ng/ml. The induced receptors are functional, because both proliferation and Ig secretion by B cells treated with anti-IgD-dextran are enhanced by IL-5. Other B cell mitogens such as LPS, soluble anti-Ig/IL-4, or phorbol esters/ionomycin are poor inducers of the IL-5R. Finally, not only does LPS fail to induce significant IL-5R expression on spleen B cells, it suppresses both high and low affinity IL-5R expression induced by anti-IgD-dextran. These data indicate that normal, non-Ly-1 B cells are capable of expressing both high and low affinity IL-5R but that receptor expression is critically dependent on the type of stimulus provided to the B cell. A stimulus that produces extensive cross-linking of surface Ig on B cells, i.e., anti-Ig-dextran, is very effective in inducing IL-5R whereas a variety of other B cell mitogens are ineffective.

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