BackgroundCCL28 (MEC) binds to CCR3 and CCR10 and recruits IgA-secreting plasma cells (IgA-ASC) in the mucosal lamina propria (MLP). Mucosal HIV-specific IgA are detected in HIV-infection and exposure. The CCL28 circuit was analyzed in HIV-infected and-exposed individuals and in HIV-unexposed controls; the effect of CCL28 administration on gastrointestinal MLP IgA-ASC was verified in a mouse model.Methodology/FindingsCCL28 was augmented in breast milk (BM) plasma and saliva of HIV-infected and –exposed individuals; CCR3+ and CCR10+ B lymphocytes were increased in these same individuals. Additionally: 1) CCL28 concentration in BM was associated with longer survival in HIV vertically-infected children; and 2) gastro-intestinal mucosal IgA-ASC were significantly increased in VSV-immunized mice receiving CCL28.ConclusionsCCL28 mediates mucosal immunity in HIV exposure and infection. CCL28-including constructs should be considered in mucosal vaccines to prevent HIV infection of the gastro-intestinal MLP via modulation of IgA-ASC.

Taken together, these results show that soluble gp120 contributes to HIV-1 replication and dissemination, via the activation of multiple cell signaling pathways and the induction of Tat-cofactor expression, underscoring its potential as a therapeutic target in HIV-1-mediated pathogenesis.

Whereas gp120 CD4-induced structures have been largely documented and at least in part elucidated by crystallization, information about gp120 coreceptor-induced structures remains incomplete despite numerous studies. In this work, mutations were carried out in a selected internal region of HIV-1/YU2 gp120, proximal to the CD4-binding site, because of its highly conserved nature among retroviruses and its high structural stability. The targeted residues, belonging to the beta16/beta17 beta-hairpin, modulate gp120 binding to CD4 and gp120-CD4 complex binding to CCR5. Thus, it appears that this gp120 structure acts as a hinge between the CD4-binding site and the putative coreceptor binding structure. Substitution of amino acid residues like E381A did not affect gp120 binding to CD4 and did not induce significant structural changes in gp120, as demonstrated by epitope analysis, BIACORE analysis, and circular dichroism. Nevertheless, E381 has a critical influence on the maintenance of CCR5 coreceptor binding by forming a salt bridge with K207. Another important element of the beta-hairpin in this interaction is the probable hydrophobic link between F383 and I420. Altogether, these results suggest that the beta-hairpin structure likely governs interactions between the surface of gp120 with native CCR5 or the CCR5 amino-terminal domain (CCR5-Nt). The mutations within the beta-hairpin had a direct effect on the proximal surface of the bridging sheet, the putative CCR5 surface, and the gp120 YU2 HIV-1-CD4 binding site. These results on the gp120-CCR5-Nt binding mechanism contribute to our understanding of CCR5 and HIV-1 gp120 association and HIV-1 entry; they may also contribute to designing novel inhibitors.

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