Here we report the cloning of the cDNA for human CD40-Ligand (CD40-L) from a CD4-positive T cell clone. The deduced amino acid sequence predicts a type II membrane protein of 261 amino acids. Northern blot and FACS analysis of PBMNC revealed that the human CD40-L can be detected on T cells and is absent from B cells and monocytes. The human CD40-L is expressed on both CD4- and CD8-positive T cells, (CD45RO+) and (CD45RA+) subsets. We observed that IL-4, an inducer of IgE production, upregulated CD40-L mRNA level while IFNy, an inhibitor of IgE synthesis, reduced the expression of CD40-L mRNA. These data suggest a the correlation between human CD40-L expression and IgE production.
