Experimental bovine trypanosomiasis (Trypanosoma vivax and T. congolense). III. Serum levels of immunoglobulins, heterophile antibodies, and antibodies to T. vivax.

Twenty-five steers were infected with T. vivax (EATRO 1721), 25 steers with T. congolense (EATRO 1800) and 25 steers kept as controls. Serum levels of immunoglobulins (IgG1, IgG2, IgM), natural antibodies to erythrocytes of chicken and sheep, and complement-fixing antibodies to T. vivax were measured. A significant decrease of serum IgM and natural antibodies to chicken erythrocytes occurred in the T. vivax group at day 9, i.e. at the decline of the first parasitemic wave. This was followed by a transient moderate increase of IgM accompanied by a transient decrease of IgG2. The T. congolense group had moderate decreases (less than 30%) of the mean IgG1 levels and moderate increases (less than or equal to 50%) of the mean IgG2, levels. It was concluded that there was little evidence for polyclonal activation of lymphocytes and that the decreased IgG1 levels in the T. congolense group might have been a reflection of immunosuppression. The complement-fixation test proved to be a sensitive tool for monitoring the antibody response to T. vivax.