Characterization of a calcium dependent immune response to human serum albumin
Frankel, M.E.; Liberti, P.A.
Journal of Immunology 125(1): 18-23
1980
ISSN/ISBN: 0022-1767 PMID: 6155395 Document Number: 157465
Ca dependent antigen-antibody reactions are well known for glutamyl containing random sequence polypeptide antigens serve as model systems for physico-chemical studies of such reactions. To develop similar systems for studying protein-anti-protein interactions, a search was made for the possible existence of Ca dependency in anti-protein reactions. An examination of antibody responses in sheep and rabbits against human serum albumin showed that all animals tested produce some antibodies that are Ca dependent. The extent of these reactions when determined with immune adsorbants varied from 1-10% of total antibodies and appears to be greater in sheep. When such reaction were abolished by EDTA addition, effects on precipitin reactions far exceeded these values. Antibodies so eluted from sheep antisera were predominantly IgG. By using a radioimmune assay system, the cation specificity of these reactions was examined and found to be highly specific for Ca, with 10 mM Ca2+ resulting in maximal reaction; an affinity constant for antigen-antibody combination of 8 .times. 108 M-1 was determined; and the absence of cross reactions for related protein antigens was found. The number of Ca dependent determinants on human serum albumin was determined from ultracentrifugal analysis of complexes formed with antigen and Fab or antibody in the presence of Ca2+ and was found to be 2.