BLC (CXCL13) is expressed by different dendritic cell subsets in vitro andin vivo

Dendritic cells (DC) attract both T and B lymphocytes to induce an efficien t antigen-specific immune response. Recently, it was shown that naive T cel ls are attracted to DC by dendritic cell chemokine 1 (DC-CK1, CCL18). The p otent B lymphocyte chemoattractant BLC (CXCL13) was previously shown to be essential for homing of lymphocytes into secondary lymphoid organs and for the development of B cell follicles. As the cells that produce BLC are larg ely unknown and BLC could be a candidate chemokine for the recruitment of B cells to DC, we analyzed different DC subsets for expression of BLC. Here we demonstrate that monocyte-derived DC as well as activated blood DC indee d express and secrete BLC. Interestingly, ligation of the CD40 molecule dow n-regulated BLC expression in monocyte-derived DC. Staining of tonsilar sec tions indicated that BLC is expressed by follicular dendritic cells and ger minal center dendritic cells (GCDC) in vivo. Real-time quantitative PCR con firmed the expression of BLC in isolated GCDC. Since both B cells and activ ated T cells express the receptor for BLC, our findings implicate an import ant role for BLC in establishing the interaction of DC with T cells and B c ells. Furthermore, CD40/CD40 ligand interactions could modulate this proces s by down-regulating the expression of BLC.