title: Enumeration of the antigenic determinants of human secretory component (SC) and secretory IgA (sIgA).
abstract: The number of antigenic determinants of human SC and sIgA was determined with specific anti-SC antibodies isolated from a pool of two hyperimmunized sheep. The Fab' antibody fragments were prepared and [125I] labelled, while pure SC and pure sIgA, isolated from colostrum, were labelled with 131I. The [125I] Fab' antibodies were added, in very large molar excess, to the [131I] antigens at various ratios. The Fab'-Ag complexes were separated from the antibody excess by gel-filtration. The highest Fab'/Ag molar ratios of the complexes, which correspond to the maximal number of accessible antigenic determinants, were calculated. We found at least 16 sites (16.6 +/- 1.36) on free SC while only 12 (12.27 +/- 0.51) were located on sIgA. These results confirm the existence of a significant number of hidden determinants of the SC subunit of sIgA and establish that about 1/4 of the SC molecule is implied in this binding.
mesh_terms: D001666:Binding Sites, Antibody; D011232:Chemical Precipitation; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D000939:Epitopes; D006801:Humans; D007070:Immunoglobulin A; D007071:Immunoglobulin A, Secretory; D007140:Immunoglobulin Fab Fragments; D007128:Immunoglobulin Fragments; D007457:Iodine Radioisotopes; D008970:Molecular Weight; D012635:Secretory Component
chemical_list: D000939:Epitopes; D007070:Immunoglobulin A; D007071:Immunoglobulin A, Secretory; D007140:Immunoglobulin Fab Fragments; D007128:Immunoglobulin Fragments; D007457:Iodine Radioisotopes; D012635:Secretory Component