Nature of immune complexes formed in rhesus monkeys immunized with Pr-B-HCG-TT on challenge with hCG

Abstract

Seven rhesus monkeys with circulating anti-hCG antibodies were challenged on repeated occasions with doubling doses of hCG. The antibody titers declined after hCG challenge. The hormone was completely bound by the antibodies and no evidence for free hCG was available by a) assay for hCG activity in the supernatants after precipitation of the antigen-antibody complexes with polyethyleneglycol (PEG), b) the absence of ¹²⁵I-hCG peak at the site corresponding to the free hormone in sucrose density gradient runs, coupled with the identification of the entire radioiodinated hCG in the antibody bound region. The hCG-anti-hCG complexes had a sedimentation constant of 175 indicating that a minimum of three IgG molecules were bound per ¹²⁵I-hCG molecule. No change in the C₃ component of the complement was found in the blood samples removed at different time periods after challenge with hCG. The hCG-anti-hCG complexes separable with graded concentrations of PEG when reconstituted in phosphate buffered saline possessed no biological activity in the Leydig cell bioassay. In three rhesus monkeys, an intravenous injection of hLH was given prior to the hCG clearance test, hLH did not cause a fall in the anti-hCG titers of the type noted with hCG challenge.