Circumoval precipitin antigens for the diagnosis of schistosomiasis. II. Isolation of functional antigens.

A serum was prepared by immunizing rabbits with circumoval precipitin (COP) immune complexes isolated by Protein A Sepharose affinity chromatography. This serum, positive in the COP test, was used to isolate by antibody affinity chromatography the COP antigens contained in crude schistosome egg antigens (SEA). The COP antigens were then applied to the enzyme-linked immunosorbent assay (ELISA) and compared to SEA. In a rabbit immunized repeatedly with the COP immune complexes the reactivity in the ELISA to both SEA and the COP antigens increased with time. In a primary infection of S. mansoni the reactivity to both antigen preparations rose in parallel; however, SEA showed higher reactivity. Interestingly, with the COP antigens a dramatic increase in antibody response was obtained in the serum of the 4th week in two separate groups of infected mice. This is probably a reflection of the common antigens between worms and eggs since two of the three major antibodies to the COP antigens identified previously are absorbable with lyophilized S. mansoni worms.