Immunologic and fine structure evidence of avidly bound host serum proteins in the surface coat of a bloodstream trypanosome.

Intact, washed Trypanosoma lewisi bloodstream forms, isolated from rats, were agglutinated specifically by antisera against rat whole serum, albumin, alpha2-macroglobulin, and IgG. However, trypsinized bloodstream and intact culture forms lacking surface coat were not agglutinated by these antisera. Trypsinized bloodstream forms, incubated in dilute rat or heterologous host serum proteins, were agglutinated with specific antisera. The characteristic surface coat of intact bloodstream forms was absent from trypsinized cells; however, trypsinized and serum-incubated bloodstream forms reacquired a surface coat similar to that of intact cells. Gel-diffusion and immunoelectrophoretic results showed that rat albumin, alpha2-macroglobulin, and IgG were present in the surface coat of bloodstream forms. Results of quantitative rocket immunoelectrophoresis demonstrated that the adsorbed rat serum proteins constituted by weight about 5% of the trypanosome total surface coat protein.