Trypanostatic activity of rat IgG purified from the surface coat of Trypanosoma lewisi.

Host IgG is a component of the surface coat of Trypanosoma lewisi; it is specifically acquired during infection in the rat, concomitant with a rise in titer of trypanostatic (ablastic) activity of host serum. Host IgG was eluted from trypomastigotes at 7 to 9 days postinfection with a high salt-low pH buffer. Surface coats and trypanosome ultrastructure were not notably altered by the elution procedure, as determined by electron microscopy. Rat IgG was removed and purified from the trypanosome eluates on an immunoadsorbent column made with the IgG fraction of anti-rat IgG serum coupled to Sepharose beads. Concentrated column eluates, by comparison with a standard, were shown to be rat IgG by immunoelectrophoresis and SDS polyacrylamide gel electrophoresis. As a control, IgG from normal rat serum was purified by the same technique. IgG-negative trypanosomes harvested from immunosuppressed rats bound IgG purified from surface coats of trypanosomes, but not IgG purified from normal rat serum, as demonstrated by subsequent labelling with FITC-conjugated, rabbit anti-rat IgG. The IgG purified from surface coats inhibited the reproduction of T. lewisi in an in vitro assay, but purified, normal IgG did not. These data show that antigen-specific host IgG, adsorbed to the surface of T. lewisi, is ablastic antibody.