The human B cell response to IL-13 is dependent on cellular phenotype as well as mode of activation

Normal mature quiescent human B lymphocytes, isolated as a function of buoy ant density, require activation for up-regulation of IL-13R constituents. C ell activation through a combination of surface Ig and CD40 receptor ligati on leads to the most substantial message production for IL-13R alpha 1. Fun ctional consequences of this receptor variation, in initially quiescent cel ls, includes demonstrable effects on cellular proliferation in response to ligand exposure. Variations in the method of surface activation, with parti cular emphasis on the CD40 receptor, reveals that immobilized CD40 ligand m ay be sufficient, in and of itself, to up-regulate IL-13R alpha 1, which ma y bear significance for B-lymphocyte bystander proliferation. Regulation of the IL-13R alpha 1 protein and message also differs as a function of cellu lar phenotype, Although values are greater in memory than naive B cells, as they are initially isolated from extirpated tonsils, variations in the mag nitude of message and protein, as a function of surface stimulation, are mo re substantial in the naive subset. The magnitude of variation in message p roduction in naive cells is associated with a more vigorous proliferative r esponse to IL-13 than seen in memory lymphocytes. The cellular response to IL-13, as a function of activation and phenotype, is the converse of that d emonstrated for IL-2. Evaluation of proliferation, receptor message, ligand binding protein production, and the response to putatively synergistic cyt okines reveals that IL-2 is the predominant lymphokine utilized by memory c ells. This is in contradistinction to IL-13, which along with IL-4, are the predominant moieties for naive lymphocytes.