Evaluation of immunoglobulin M western blot analysis in the diagnosis of congenital syphilis

Abstract

Western immunoblots of solubilized Treponema pallidum antigens were reacted with sera and cerebrospinal fluid (CSF) and developed with enzyme-conjugated antibodies to immunoglobulin M (IgM). A blot was considered positive if reactions included bands at the 47-, 17-, and 15.5-kilodalton positions along with a variable pattern at other low-molecular-weight positions. Sera from 23 of 25 symptomatic infants diagnosed with congenital syphilis yielded positive reactions. Of 80 asymptomatic infants considered at risk for developing symptomatic infection, 16 exhibited IgM patterns consistent with those seen in congenital syphilis, although 5 of these 16 gave reactions that were equivocal. To exclude false-positive reactions due to IgM rheumatoid factor, sera were fractionated and the IgM fractions were retested. Only the five initially equivocal sera gave nonreactive blots with the IgM fractions, whereas all others gave more prominent reactions that were qualitatively similar to those seen in serum samples. Sera from 18 normal infants failed to show any IgM reactivity to T. pallidum antigens on Western blots. The IgM Western blot was both more sensitive and more specific than the fluorescent treponemal antibody-absorbed (IgM) test using fractionated serum. Of the 17 CSF samples from infants with symptomatic congenital syphilis, 14 showed IgM reactivity in Western blots, whereas only 12 had a reactive CSF in the Venereal Disease Research Laboratory test. Our results indicate that this technique can be used to identify both symptomatic and asymptomatic infection in infants with T. pallidum, in some cases before standard serologic studies can confirm the diagnosis.