Immunoglobulin A antibody response to respiratory syncytial virus structural proteins in colostrum and milk

Immunoglobulin A (IgA) antibody response to respiratory syncytial virus (RSV) structural proteins in colostrum and milk was investigated by a radioimmunoprecipitation assay. By using [35S]methionine-labeled RSV-infected HEp-2 cells and antiserum to human IgA as the capture antibody, IgA antibody responses to large glycoprotein, fusion protein, nucleoprotein, phosphoprotein, and matrix protein were demonstrated in colostrum and milk. The IgA antibody response was mainly directed against fusion protein, whereas IgA activity against matrix protein was more variable and was not comparable to the antibody responses to other structural proteins. Maternal mammary IgA response after RSV infection in the infant was monitored in four cases, and the appearance of anti-RSV IgA activity against several RSV structural proteins was observed in convalescent-stage milk samples of two mothers in whom RSV infection was demonstrated.