Differential susceptibility of rabbit sIgA subclasses to trypsin cleavage: characterization of the fragments obtained from the g subclass
Tseng, J.; Knight, K.L.
Journal of Immunology 115(2): 454-461
1975
ISSN/ISBN: 0022-1767 PMID: 807638 Document Number: 84369
Rabbit secretory IgA (sIgA) was digested with trypsin at 37 deg C for 30 min and 4 fractions were isolated by gel filtration. These fragments were characterized by ultracentrifugation, and by their antigenic properties as undigested sIgA, Fab2 alpha and Fc2 alpha . (Two Fc2 alpha fragments differing in their content of secretory component were obtained.) The IgA-f subclass molecules were resistant to cleavage and were found in the undigested sIgA fraction; the IgA-g subclass molecules were cleaved into Fc2 alpha and Fab2 alpha fragments. The g allotypic determinants of IgA-g molecules were found on both the Fc2 alpha fragments and the Fab2 alpha fragments. The Fc2 alpha and Fab2 alpha fragments obtained from trypsin-digested sIgA were compared by means of antigenic properties and peptide maps with the Fc2 alpha and Fab2 alpha fragments obtained from papain-digested sIgA; no differences attributable to the alpha -chain were found. Thus, papain and trypsin cleave the alpha -chain of IgA-g molecules at similar but not necessarily identical positions.