An anti-human mu chain monoclonal antibody: use for detection of IgM antibodies to Toxoplasma gondii by reverse immunosorbent assay.

A precipitating anti-human mu chain monoclonal antibody (designated Tibi 82 McAb) was produced by the cell fusion technique. This McAb (isotype: IgG1 kappa) reacted by radioimmunoassay with all 10 human IgM proteins tested. In contrast, no reactivity was observed with IgG, IgA, IgE, lambda and kappa chains. 19 S IgM proteins were precipitated by Tibi 82 McAb using the Ouchterlony method under standard conditions. Hence specificity of this McAb for the C mu 2 domain was characterized by inhibition of precipitin reactions using human IgM fragments. Despite its narrow specificity for the C mu 2 domain, such a McAb could be used for IgM capture in the detection of specific IgM to Toxoplasma gondii employing the IgM immunosorbent agglutination assay (IgM-ISAGA). Tibi 82 McAb was compared with 3 anti-human IgM polyclonal reagents in the routine analysis of 117 sera. With 2 of them, a correlation coefficient of 0.976 was obtained and Tibi 82 McAb was more sensitive than the third polyclonal reagent tested. The IgM-ISAGA technique was shown to be reproducible using Tibi 82 McAb and similar anti-human mu chain McAbs could permit the wider development of reverse immunosorbent methods for the detection of specific IgM in various infectious diseases.