The Radioimmunoassay of Serum and Salivary Blood Group A and LeaGlycoproteins

S ummary . A radioimmunoassay was developed for the detection of A and Le a blood group activities in glycoprotein fractions extracted with perchloric acid (PCA) from normal serum. The technique was also applied to studies of salivary blood group glycoproteins. Blood group A activity was detected in all group A sera tested. Higher levels of A activity were found in sera from group A 1 than from A 2 donors, and sera from both group A 1 and A 2 secretor donors gave higher levels of A activity than sera from non‐secretor donors. No difference was found in the levels of A activity in group A 1 and A 2 secretor salivas but only small numbers were assayed. Parallel radioinimunoassay inhibition lines, indicating immunological identity, were obtained with PCA‐extracts of A 1 and A 2 secretor plasma and with extracts of A 1 and A 2 secretor salivas. Le a activity was detected in all sera tested. The levels of Le a activity were higher in sera from Le(a + b ‐) donors than from h(a ‐ b +) or Le(a ‐ b ‐) donors and were unaffected by ABO group. Radioimmunoassay inhibition lines indicated qualitative differences in the Le a antigen in salivas from secretors and non‐secretors, consistent with a lower density of Le a antigen on salivary glycoprotein from secretor donors.