IL-4 induces conformational change of CD20 antigen via a protein kinase C-independent pathway. Antagonistic effect of anti-CD40 monoclonal antibody

Abstract

The CD20 molecule is a unique phosphoprotein exclusively expressed on B cells during most stages of B cell ontogeny. We here report that rIL-4 down-regulates the expression of CD20 with anti-Leu-16 mAb (clone L27) on both unstimulated and anti-mu preactivated normal and leukemic B cells. None of the other recombinant lymphokines tested (IL-1, IL-2, IL-3, IL-6, IFN-α, and IFN-γ, granulocyte/macrophage-CSF, transforming growth factor-β, TNF-α, and lymphotoxin) decreased CD20 expression. Incubation of unstimulated or anti-mu preactivated B cells with IL-4 did not affect the steady state CD20 mRNA, suggesting that IL-4 exerted its effect mainly at a nontranscriptional level. Hence, IL-4 selectively down-regulates the CD20 epitope recognized by clone L27 without affecting seven other different epitopes, indicating that IL-4 acts by modifying the conformation of the CD20 molecule rather than by inhibiting its production or inducing its internalization. IL-4 most likely utilizes a protein kinase C-independent signal transduction pathway to modify CD20 molecule inasmuch as staurosporine, an inhibitor of protein kinase C, antagonizes phorbol esters (PMA) but not IL-4-induced CD20 down-regulation. In contrast, anti-CD40 mAb reverses the IL-4 but not the PMA inhibitory effect on CD20 expression. Given that CD20 may be part of a Ca2+ ion channel and plays a role in B cell activation and proliferation, it is proposed that the ability of anti-CD40 mAb to maintain the CD20 molecule in a given epitopic configuration on IL-4-stimulated B cells may be related to the long term proliferation of normal B cells that are strictly dependent on the presence of IL-4 and cross-linked anti-CD40 mAb for their continuous growth.