Immunoglobulin studies in serum of patients with American trypanosomiasis (Chagas' disease).

Individuals with acute American trypanosomiasis had normal serum concentration of immunoglobulins-G, -A and -M. In the chronic stage they had normal levels of serum IgA and IgM, and a small but significant increment in IgG. Anti-trypanosome antibodies of the IgM class were regularly found in the acute stage but only occasionally in the chronic stage. IgG and IgA specific antibodies were present in both stages, but titres were higher during the chronic phase. No abnormalities were observed in the levels of immunoconglutinins or in the presence of rheumatoid factors and antinuclear factors. High titres of anti-sheep and anti-rat red blood cell (RBC) antibodies appeared early in the acute phase. Anti-sheep RBC agglutinins could be removed completely by absorption with rat RBC, but anti-rat RBC agglutinins could be absorbed only partially with sheep RBC. Antigens responsible for the heterophile reaction were localized to the external surface of culture forms of .