CD40LG and syphilis: ,40, 41, 42 Positive results are observed after B. burgdorferi infection due to the long-lasting persistence of antibodies in serum for decades, in endemic regions with high seroprevalence (up to 50% in highly exposed populations), or with the IgM ELISA in the context of other conditions (i.e., syphilis, infectious mononucleosis, or autoimmune diseases) due to unspecific stimulation of B cells.8