Distribution of IgG subclasses in human colostrum and milk

Abstract 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 IgG 1 was significantly increased and that of IgG 2 was decreased in both colostrum and milk relative to the percentage distribution reported in healthy adult and maternal sera. Percentages of IgG 3 and IgG 4 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 IgG 1 in colostrum and milk is discussed.