Quantification of IgA and IgG and specificities of antibodies to viral proteins in parotid saliva at different stages of HIV-1 infection

Abstract

Paired sera and parotid saliva from 75 HIV-1-infected patients, divided in three equal groups with CD4⁺ cell counts > 500, 200–500 and < 200/mm³, respectively, were analysed for IgG, IgA and secretory IgA (sIgA) concentrations and for IgG and IgA antibody directed to HIV-1. Twenty-nine age-matched HIV⁻ subjects were used as controls. In serum the concentrations of immunoglobulins were significantly increased in HIV-infected subjects compared with controls, and a progressive increase of IgA and sIgA was noticed while the CD4⁺ cell count decreased. In contrast, concentrations of IgA and sIgA were not different in parotid saliva between the four subject groups. By an ELISA test directed towards HIV-1 proteins, 73 of the 75 serum specimens from the HIV-infected subjects (97%) and 43 of the corresponding saliva (57%) were found positive for specific IgA antibodies to HIV-1, with an even distribution among the three groups of patients. By Western blotting multiple specificities of IgA to HIV-1 proteins were not frequently found in patients. By contrast, in spite of an IgG concentration in saliva about 100 times lower than that of IgA, reactivities were significantly higher for IgG than for IgA antibodies, especially to env and to pol HIV-1 products. Altogether, these data suggest that the regulation of IgA production in HIV-infected subjects is independent in serum and in parotid saliva. This imbalance of IgA/IgG antibodies to HIV-1 at the mucosal level appears to be a specific feature of HIV-1 infection, and may raise important issues in terms of local protection after immunization.

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