Distribution of IgG subclasses in human colostrum and milk.

Immunoglobulin G (IgG) subclasses in human colostrum and milk were quantitated using mouse monoclonal antibodies specific for human IgG subclasses and an enzyme-linked immunosorbent assay (ELISA). The percentage of IgG1 was significantly increased and that of IgG2 was decreased in both colostrum and milk relative to the percentage distribution reported in healthy adult and maternal sera. Percentages of IgG3 and IgG4 in colostrum, milk and sera were similar. All IgG subclass concentrations decreased by 90% during the first week of lactation and remained constant thereafter. The possible antiviral role of high levels of IgG1 in colostrum and milk is discussed.