The presence of secretory component-free human colostral IgA in early colostrum

Human secretory IgA was prepared from colostrum. Different elution diagrams from CM-cellulose were obtained depending on the time of collection of colostrum. In case of early colostrum, collected within 6 hours post partum, two IgA fractions were obtained after chromatography on CM-cellulose. Both fractions have different molecular weights and different amino acid compositions. The results obtained suggest that the first fraction is a dimer of IgA monomers containing J chain with a molecular weight of 330,000 whereas the second fraction having the molecular weight 395,000 daltons is composed of IgA dimer, J chain and SC. When colostrum collected 48 or more hours was used as a source of IgA, only the second IgA fraction was obtained. The problem of SC-free IgA immunoglobulins is discussed.