Simplified chromatographic separation of immunoglobulin M from G and its application to toxoplasma indirect immunofluorescence

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Abstract
The indirect immunofluorescent (IFF) antibody technique for the detection of T. gondii immunoglobulin M (IgM) often gives false negative results, probably due to the competition between IgG and IgM. A gel filtration procedure for the separation of IgG and IgM was adapted to a routine diagnostic test capable of handling at least 10 sera/day and requiring only 50 .mu.l of serum. The results from 108 sera [human] having positive complement fixation titers for Toxoplasma showed that 17 were IgM positive when the whole serum was tested by IIF compared with 55 positive when the IgM fraction was used. Sera with anti-DNA titers did not give false positive results after fractionation, and the removal of IgG eliminated false positive results due to rheumatoid factor. A prospective study showed that Toxoplasma IgM may persist up to 9 mo.