Identification of an antigen-specific immunoglobulin M antibody associated with acute Toxoplasma infection.

We used the protein gel transfer technique (Western blotting) to analyze the immune response to individual electrophoretically resolved Toxoplasma antigens. Toxoplasma antigens were fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The array of resolved proteins was electrophoretically transferred to CNBr-activated filter paper and incubated with serum samples from patients with either acute or chronic Toxoplasma infections or with serum samples from seronegative controls. Serum immunoglobulin G and immunoglobulin M bound to individual Toxoplasma antigens were detected by radioiodinated staphylococcal protein A and a goat anti-human immunoglobulin M antibody, respectively. A complex array of Toxoplasma antigens was revealed by this procedure. Immunoglobulin M directed against a low-molecular-weight antigen was detected in sera from all acutely infected adults (19 sera tested) and was absent from all sera from individuals with chronic infections (9 sera tested) and from sera from seronegative controls (9 sera tested).