Demonstration of Toxoplasma antigen containing complexes in active toxoplasmosis

Abstract

With an enzyme-linked immunosorbent assay antigen, specific circulating immune complexes (CIC) were demonstrated in experimental and human toxoplasmosis. In experimentally infected mice, CIC became demonstrable as soon as antibodies appeared after fatal infection. When a nonvirulent strain of Toxoplasma was used CIC remained detectable for several weeks. This period was characterized by clinically healthy animals with increasing antibody titers and by cysts growing in the brains of the animals, indicating a subacute stage of the toxoplasma infection. In the human sera, a surprisingly high percentage of CIC was demonstrated. Both immunoglobulin G (IgG) and IgM were found in the CIC; however, IgG was seen in the majority. If the humans were grouped according to other serological results, such as a combination with IgM antibodies, circulating antigens, or both, or a positive complement fixation test, increasingly more CIC were observed. When sera were selected from patients with clinical symptoms generally associated with toxoplasmosis, more CIC were also again demonstrated. On the contrary, in healthy individuals (blood donors), CIC were also regularly observed, suggesting that exacerbations of latent infections or reinfections may regularly occur without leading to clinical signs. In conclusion, we propose that the interpretation of a positive CIC test requires great care but may provide useful information about the activity of a toxoplasma infection.

Immunity to internal parasites

“…Serodiagnosis of Toxoplasma gondii is readily achieved by radioimmunoassay (14) where the host animal has been infected several weeks previously. However, antigenaemia can be detected during early acute toxoplasmosis by ELISA (2) and so also can circulating immune complexes (46). Because cryptosporidiosis is usually a problem in the very young animal it is probably best diagnosed by faecal examination.…”

Presence of high concentrations of circulating Toxoplasma antigens during acute Toxoplasma infection in athymic nude mice

“…In these cases, a direct detection of antigenic components of Toxoplasma gondii in sera or body fluids might be a valuable aid in the rapid and specific diagnosis of acute toxoplasmosis. Recently, it was reported that circulating Toxoplasma antigens (c-Ag) are detectable in sera from humans and animals with acute toxoplasmosis by countercurrent electrophoresis (8), enzyme-linked immunosorbent assay (1,3,14,15), dot immunobinding (2), and radioimmunoassay (4). We have previously reported a simple agglutination test which uses latex particles coated with anti-Toxoplasma antibodies (Ag-LA) for the detection of c-Ag (10).…”