Modulation by human milk of IgG subclass response to hepatitis B vaccine in infants

The influence of breast and formula feeding on specific anti-hepatitis B surface antigen (HBsAg) IgG subclass production and distribution has been investigated in 40 healthy infants, born to HBsAg-positive mothers and vaccinated against hepatitis B virus (HBV). Twenty children were bottle fed and 20 were breast fed. Specific subclasses were detected at the 4th and 12th months using an enzyme-linked immunosorbent assay with monoclonal antibodies. A defect in total IgG and IgG subclasses was previously excluded. Significant differences were observed both at the 4th and 12th months for IgG1 and IgG2. Breast-fed infants had significantly higher levels of specific IgG2 (about three times higher), while IgG1 levels were significantly higher in formula-fed infants. Anti-HBsAg IgG4 levels were always higher in bottle-fed infants, but a statistical significance was never present. No difference was found in specific IgG3 levels. This study reports the evidence that breast feeding influences specific IgG subclass synthesis against a viral antigen and suggests an immunologic modulation of the response to vaccines dependent not only on age but also on factors present in human milk.