B lymphocyte-derived IL-16 attracts dendritic cells and Th cells

Interaction of B lymphocytes with Th cells is a fundamental step in the est ablishment of humoral immunity, and recent evidence suggests that direct in teraction between B lymphocytes and dendritic cells (DCs) is also an import ant prerequisite, Factors involved in the selective recruitment of Th cells and DCs by B lymphocytes are insufficiently defined. We set out to delinea te the role of IL-16, the soluble ligand of CD4, which is expressed on Th c ells and DCs. B lymphocytes express IL-16 mRNA and synthesize bioactive IL- 16 protein, and IL-16 is expressed in lymph node follicles in situ, B lymph ocyte supernatant efficiently induces migration of CD4(+) Th cells, monocyt e-derived DCs, and circulating blood DCs in nitrocellulose filter-based ass ays, Neutralization of IL-16 bioactivity strongly inhibits this migratory r esponse, suggesting that IL-16 might be a major chemotactic factor derived from B cells. The present data further support the idea that IL-16 might ha ve a role in the initiation of cellular as well as humoral immunity by medi ating the cellular cross-talk among T lymphocytes, B cells, and DCs, leadin g to recruitment of these cell types at common anatomical sites.