IgM ANTIBODIES IN ACUTE TOXOPLASMOSIS: I. DIAGNOSTIC SIGNIFICANCE IN CONGENITAL CASES AND A METHOD FOR THEIR RAPID DEMONSTRATION

Abstract

The present study was undertaken to develop a simple technique for demonstration of IgM-toxoplasma antibodies in acute congenital toxoplasmosis. Such antibodies were demonstrable by each of the four methods used, but their sensitivities varied considerably. The underlying difficulty in interpretation of results obtained in the dye and hemagglutination tests following reductive cleavage appeared to be the high titer of IgG-toxo-plasma antibodies in all sera tested, which "hides" the effect of 2-ME on the IgM-toxoplasma antibodies. Because IgG-toxoplasma antibodies do not interfere with the demonstration of IgM-toxoplasma antibodies in fractions obtained by sucrose density gradient ultracentrifugation or with the IgM-fluorescent antibody test, these two methods proved the most sensitive for demonstration of IgM-toxoplasma antibodies in congenital cases. Whereas the former of these two methods is a laborious procedure requiring facilities rarely available in clinical laboratories, the IgM-fluorescent antibody test is easily learned and it can be performed in 2 hours. Serologic diagnosis of infection in newborns is often complicated by the presence in the infant of maternal antibodies. The difficulty in interpretation of serologic results in cases of suspect congenital toxoplasmosis is magnified by the high prevalence of toxoplasma antibodies in the normal childbearing population (and thus in their offspring). Demonstration of IgM antibodies in newborn infants (in the absence of a placental leak) appears to be diagnostic of congenital toxoplasmosis. Because of the difficulty encountered in recognition of congenital cases which do not appear to have the "classical" signs and because of the infrequency with which the diagnosis can be established, even in these latter cases, the IgM-fluorescent antibody test will hopefully prove simple enough to perform to be useful as a test for the definitive diagnosis of acute congenital toxoplasmosis.