Radioimmunoassay of "pregnancy-specific"-beta 1-glycoprotein (SP1).

A radioimmunoassay for SP1 ("pregnancy-specific" beta 1-glycoprotein) is described in which a sensitivity of 0.1 microgram/L was achieved by use of an antiserum with Ka approximately equal to 1.7 x 10(11) L/mol and delayed addition of a 125I-SP1 tracer (specific acty, 25 Ci/g) that was stable for use in the assay for at least six to seven weeks. We also report an additional anti-SP1 serum, from an early bleeding, that displayed "apparent positive cooperativity" in the IgG but not the IgM fraction.