A surface glycoprotein of Trypanosoma lewisi binds immunoglobulin G from the serum of uninfected rats.

Detergent extracts of whole Trypanosoma lewisi were fractionated by polyacrylamide gel electrophoresis and transferred to nitrocellulose for immunoblotting analysis. Antibody probes to rat immunoglobulin G (IgG) and IgM detected intact gamma chains, mu chains, and light chains in extracts. The amount of immunoglobulin detected increased as the infection progressed. Transfers were also incubated in serum from conventionally reared (CRS), specific-pathogen-free (SPFS), or germ-free rats before being probed with anti-rat IgG or anti-rat IgM. Components of 200, 175, and 120 kilodaltons (kDa) bound IgM from all sera tested and were present in extracts of trypanosomes isolated from lethally irradiated or intact rats on different days during infection. No parasite components bound IgG from serum of germ-free rats. However, 145-, 175-, and 200-kDa components bound IgG from CRS and SPFS. A 74-kDa protein was the major IgG-binding component in extracts of reproducing parasites. This component bound much more IgG from CRS than it bound from SPFS. The 74-kDa protein was removed from parasites by mild trypsinization and corresponded to a major surface glycoprotein detected when intact cells were radioiodinated. These results indicate that natural antibodies to T. lewisi exist in rats or that these parasites have surface proteins that bind immunoglobulins without regard to antigenic specificity.