CD40 ligand is functionally expressed on human eosinophils.

CD40 ligand (CD40L), a surface molecule which can be expressed by T cells, mast cells and basophils, has been shown to be involved in the control of B cell proliferation, immunoglobulin class switching as well as in the activation of monocytes and T cells. We demonstrate that CD40L can also be expressed constitutively by eosinophils from an hypereosinophilic patient or, upon activation, by the eosinophilic cell line EOL-3 and normal blood eosinophils. Eosinophils were able to induce, in conjunction with IL-4, CD40L-dependent B cell proliferation in vitro. These results suggest that CD40L could play a role in the inflammatory processes during which eosinophil infiltration and activation are observed.

Human CD40-ligand: molecular cloning, cellular distribution and regulation of expression by factors controlling IgE production.

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, (CD45R0+) and (CD45RA+) subsets. We observed that IL-4, an inducer of IgE production, upregulated CD40-L mRNA level while IFN gamma, 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.