Abstract
Summary
A frozen and thawed extract of toxoplasma-infected rabbit brain (but not similar extracts of certain other heavily parasitized tissues) yielded an antigen which fixed complement specifically in the presence of immune sera from experimentally infected rhesus monkeys but not rabbits, dogs, and cats. This complement fixing antibody appeared within 1 to 4 weeks after inoculation, but unlike the neutralizing antibody disappeared again in most monkeys, sometimes as early as 2 months. A certain number of human beings who were known or suspected to have experienced toxoplasmic infection also gave positive complement fixation reactions. However, twenty selected individuals whose sera had neutralizing antibodies against toxo-plasma gave negative complement fixation reactions, but in none of these was there evidence of recent or active infection. While a positive complement fixation reaction does not in all cases indicate active or even recent infection, it is believed that this test may have its greatest usefulness in the rapid diagnosis of active toxoplasmosis.
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