Differential expression of IL-4 receptors in human T and B lymphocytes.

IL-4R have been described in unstimulated human T and B lymphocytes. However, a precise comparative study on the expression and regulation of IL-4R in isolated human T and B cell populations has not yet been fully assessed. We examined the mRNA levels and the cell membrane expression of IL-4R in freshly isolated T and B lymphocytes as well as in in vivo- and in vitro-stimulated cells. IL-4R protein expression and transcript levels were higher in tonsillar unstimulated B cells than in T cells. Splenic and peripheral blood B lymphocytes also expressed higher surface IL-4R in their membranes than T cells did. Large B lymphocytes from tonsils (in vivo-activated cells) obtained by Percoll gradient centrifugation displayed higher IL-4R levels than resting cells. On activation in vitro of T lymphocytes with IL-2 or PHA, slight increments on the IL-4R mRNA and protein levels were achieved. However, maximal levels of IL-4R expression were obtained on T cell incubation with IL-4 at a concentration of 100 U/ml. Similarly, the same concentration of this lymphokine up-regulated the surface IL-4R molecules and the IL-4R mRNA levels in purified B lymphocytes. Cross-linkage of surface Ig by insolubilized anti-IgM potentiated the effect of IL-4 in up-regulating IL-4R expression in B cells, probably by inducing outgrowth of IL-4R positive subpopulations. The B cell mitogen, Staphylococcus Aureus Cowan I, although inducing cell proliferation, was ineffective in promoting new receptor synthesis. Cell proliferation was not required for IL-4-dependent IL-4R up-regulation on both T and B lymphocytes.