Diagnostic and biological significance of anti-p41 IgM antibodies against Borrelia burgdorferi

We performed a prospective study to investigate the biological significance and diagnostic specificity of anti-p41 immunoglobulin (Ig)M antibodies aga inst Borrelia burgdorferi. During a 1-year interval 2403 patients were refe rred to our department for B, burgdorferi serology. Sixty-three patients ha d repetitive positive tests for IgM anti-p41 antibodies and negative tests for anti-p41 IgG antibodies. Ten of the 63 patients recently had symptoms o f erythema migrans. A confirmatory IgM Western blot gave a positive reactio n in 5 patients out of 53 patients with little or no clinical evidence of B . burgdorferi infection. The remaining 48 patients were negative in this te st and were considered as false-positives. Two whole cell enzyme-linked imm unosorbent assay (ELISAs), two immunofluorescence assays and Western blotti ng were not useful as confirmatory tests. Sera from 330 blood donors and 72 cord sera were also screened for anti-p41 IgM. Five blood donor sera and f ive cord sera showed an IgM reactivity against p41, Based on our data we hy pothesize that up to 1.5% of the population may have natural IgM antibodies against p41 in their sera. We observed that six out of nine sera with such antibodies could immobilize a B, afzelii reference strain in vitro. Whethe r anti-p41 IgM antibodies are capable of inactivating infective spirochetes and thereby prevent infection in vivo is, however, not yet clarified. The paradoxical conclusion that anti-p41 IgM antibodies may be a sign of resist ance to infection rather than a sign of infection should be given considera tion.