José M. Rodríguez Frade

The chemokine SDF‐1α triggers a chemotactic response and induces cell polarization in human B lymphocytes

We studied the expression and possible functional role of chemokine receptors CXCR3, CXCR4 and CCR5 in normal human B lymphocytes. B cells from both peripheral blood and tonsils expressed high levels of CXCR4 but not the other chemokine receptors tested. CXCR4 ligand, stromal cell‐derived factor (SDF)‐1α, elicited a potent chemotactic response and induced a polarized motile phenotype in B cells, resulting in redistribution of the adhesion molecule ICAM‐3 to a posterior appendage of the cell, termed uropod, and of CXCR4 receptor to the leading edge of migrating B cells. Time‐lapse videomicroscopy studies revealed that SDF‐1α‐treated cells recruited additional bystander B cells through the uropod. SDF‐1α induced levels of cellular recruitment comparable to those elicited by polarization‐inducing anti‐ICAM‐3 monoclonal antibody, in an LFA‐1/ICAM‐1, −3‐dependent fashion. Moreover, this chemokine increased intracellular Ca2+ levels in B lymphocytes, and induced a rapid CXCR4 receptor down‐regulation on the cell surface membrane. These results provide new insight into the important biological role of SDF‐1α in physiological processes in which B cells participate, and suggest a key role for chemokines in normal B cell trafficking and recirculation.

CCR5/CD4/CXCR4 oligomerization prevents HIV-1 gp120IIIB binding to the cell surface.

Significance HIV-1 enters host cells via CD4 and the coreceptors CXCR4 or CCR5. Most HIV-1 variants isolated from newly infected individuals use CCR5 (R5 strains) and infect Th1 cells, among other cell types. In ∼50% of patients, R5 strains shift to X4 strains (which use CXCR4) and infect mainly Th2 cells, leading to poor prognosis and rapid disease progression. In Th2 cells, CD4 and CXCR4 levels resemble those of Th1 cells, but they express little CCR5. We report that CCR5 expression in CD4+ T cells reduced X4 strain cell entry and infection; the molecular mechanism involves CD4/CXCR4/CCR5 oligomer formation. CCR5 expression altered CD4/CXCR4 heterodimer conformation, blocking virus binding. Oligomeric complexes should thus be considered a target for reducing HIV-1 binding and infection. CCR5 and CXCR4, the respective cell surface coreceptors of R5 and X4 HIV-1 strains, both form heterodimers with CD4, the principal HIV-1 receptor. Using several resonance energy transfer techniques, we determined that CD4, CXCR4, and CCR5 formed heterotrimers, and that CCR5 coexpression altered the conformation of both CXCR4/CXCR4 homodimers and CD4/CXCR4 heterodimers. As a result, binding of the HIV-1 envelope protein gp120IIIB to the CD4/CXCR4/CCR5 heterooligomer was negligible, and the gp120-induced cytoskeletal rearrangements necessary for HIV-1 entry were prevented. CCR5 reduced HIV-1 envelope-induced CD4/CXCR4-mediated cell-cell fusion. In nucleofected Jurkat CD4 cells and primary human CD4+ T cells, CCR5 expression led to a reduction in X4 HIV-1 infectivity. These findings can help to understand why X4 HIV-1 strains infection affect T-cell types differently during AIDS development and indicate that receptor oligomerization might be a target for previously unidentified therapeutic approaches for AIDS intervention.