CD40LG and syphilis: One limitation of serology is that serum from individuals with Epstein-Barr viral infections (mononucleosis), rheumatoid arthritis, Bartonella infections, or other spirochetal infections (e.g. periodontitis, syphilis) may exhibit cross-reactivity with B. burgdorferi IgM or IgG ELISA and Western blot assays [48–54].