Low molecular weight-IgM antibody in syphilis detected by Treponema pallidum immune adherence (TPIA) test.

Sera obtained from patients with syphilis were subjected to gel filtration chromatography to estimate antibody activity in the fractions by means of Treponema palludum immune adherence (TPIA) test. Antibody activity was found in IgM and IgG fractions and in the intermediate fraction between them. The TPIA activity of the intermediate fraction was depleted by an immunosorbent coupled with anti-mu chain antibody but not by that coupled with anti-alpha chain antibody. After separation by gel filtration and affinity chromatography, the fraction with the TPIA activity showed a positive precipitation reaction against anti-mu chain antiserum but a negative reaction with anti-alpha chain or anti-gamma chain antiserum. The antibody activity in this fraction was thus confirmed to be mainly due to low molecular weight-IgM antibody. In untreated patients with primary and secondary syphilis, the TPIA activity was demonstrated with high frequency in the low molecular weight-IgM fraction and it decreased gradually after treatment, although lowered activity persisted over a long period of time. Late syphilis cases did not show any appreciable change in TPIA activity in this fraction even after treatment.