Neutralizing antibodies in mucosal secretions: IgG or IgA?

The mucosal immune response to HIV weighs in heavily on the battle against it, as the majority of infections occur via the mucosal route. The antibody response in the mucosae, specifically the genital tract, is characterized by binding and, in some studies, neutralizing HIV-specific IgG and IgA antibodies. Ample evidence, however, points to discrepancies and difficulties in the detection of HIV-specific IgA in HIV-positive subjects, and an even more pronounced divide surfaces in studies done with individuals exposed to HIV, but uninfected. Reports in the literature detail HIV-specific (in some cases, neutralizing) IgA antibodies, in the absence of specific IgG, in the serum and mucosal secretions of virus-exposed, seronegative subjects; this has given rise to speculation that HIV-specific IgA provides a protective immune response to the virus in high-risk individuals who remain seronegative. Contradictory results, however, describe the absence of both IgA and IgG HIV antibodies in the mucosal secretions of similar cohorts. Considering the importance of the antibody response to ascertaining the correlates of HIV immunity, as well as on vaccine research and development, this review addresses the relevant studies and their implications.