Identification of a low moleculr weight IgM antibody with treponema pallidum specificity in sera of patients with chronic syphilis.

A low-molecular (8S) treponema-specific IgM antibody was isolated by means of Sephadex 200 G gel filtration and/or sucrose gradient ultracentrifugation in 78 of 4,120 sera of patients who had been identified to have had syphilis. The IgM specificity can be shown by indirect immunofluorescence using a mu-chain specific antiserum. The low molecular IgM (LMW-IgM) antibodies are not identical with the 19S-IgM as demonstrated in studies with gel filtration and sucrose gradient methods. They are not identical neither with 7S IgG or IgA. Neither the presence of antinuclear nor rheumatic factor could be shown in the LMW-IgM fraction. In most of the patients with LMW-IgM antibody, there existed a treponema infection of late latency.