CD40 LIGAND IS FUNCTIONALLY EXPRESSED ON HUMAN EOSINOPHILS

CD40 ligand (CD40L), a surface molecule which can be expressed by T ce lls, mast cells and basophils, has been shown to be involved in the co ntrol of B cell proliferation, immunoglobulin class switching as well as in the activation of monocytes and T cells. We demonstrate that CD4 0L can also be expressed constitutively by eosinophils from an hypereo sinophilic patient or, upon activation, by the eosinophilic cell line EOL-3 and normal blood eosinophils. Eosinophils were able to induce, i n conjunction with IL-4, CD40L-dependent B cell proliferation in vitro . These results suggest that CD40L could play a role in the inflammato ry processes during which eosinophil infiltration and activation are o bserved.