Immunoglobulins of colostrum. V. Localization of structural differences between serum and colostral ovine and bovine IgG1 and IgG2 immunoglobulins.

Studies on localization of structural differences between ovine and bovine serum and colostral IgG immunoglobulins are described. Comparison of heterogeneity, susceptibility to proteolytic enzymes, peptide maps, amino acid compositions, and antigenic properties of immunoglobulins and their Fab and Fc fragments and H and L chains showed that structural differences are localized in the Fc region. The strongest differences were found in case of IgG2. It was also shown that no Fc fragments could be obtained from bovine serm IgG2 and ovine serum and colostral IgG2 due to their susceptibility to papain and trypsin. The results obtained confirmed our suggestion that colostral IgG2 are locally synthesized in mammary glands, whereas colostral IgG1 might be a mixed population of molecules locally synthesized and transferred from the serum.