Quantitative and qualitative assay of rubella IgA antibody in breast milk.

Breast milk contains immunological factors, such as IgA antibody, which help to prevent infectious diseases. A total of 197 paired samples of colostrum and breast milk was collected from postpartum mothers in Gunma City, Japan, and examined for anti-rubella IgA antibody by enzyme-linked immunosorbent assay (ELISA) and Western blotting (WB). The anti-rubella virus IgA ranged from 0.5 to 78.5 U/ml with a mean of 6.05 U/ml and a median of 3.6 U/ml in colostrum, and from 0.5 to 32.7 U/ml with a mean of 2.74 U/ml and a median of 2 U/ml in milk. The differences between the means of titers of total IgA and anti-rubella virus IgA in colostrum and in milk were significant statistically. The levels of anti-rubella virus IgA in both colostrum and breast milk correlated positively with the anti-rubella virus hemagglutination inhibition (HI) titers in the sera of mother, indicating that the levels of these different classes of antibodies correlated. Based on WB, anti-rubella virus IgA in both colostrum and breast milk reacted with the rubella viral protein E1 and C, but not with the E2 protein.