Secretory IgA as a measure of resistance to infectious disease: comments on Stone, Cox, Valdimarsdottir, and Neale.

We examined recent assertions of Stone, Cox, Valdimarsdottir, and Neale regarding the use of S-IgA concentrations in whole saliva as a measure of mucosal immune competence. Our conclusions are markedly different from theirs. In this article, we report the results of a meta-analysis that reveals a significant relation between psychosocial variables and salivary S-IgA concentrations. Second, we note that an inverse relation between salivary flow and S-IgA would not preclude studying salivary S-IgA concentration. Third, we present a different perspective on the assertion of Stone et al that IgA proteases in whole saliva potentially lead to erroneous results from the radial immunodiffusion assay. Fourth, we report a meta-analysis suggesting a statistically significant relation between S-IgA salivary concentrations and the incidence of acute upper respiratory illnesses. We conclude that there is no empirical or logical reason to prefer the measurement of another aspect of immunity to total S-IgA concentration in whole saliva.