The most prevalent chronic human autoimmune disorder worldwide is rheumatoid arthritis [3], and it is noteworthy that Fujita et al. found a 30% prevalence of C. pneumoniae immunoglobulin M (IgM) in 27 patients in the acute phase of this illness (compared with a prevalence of 10% in controls) [1]. This evidence concerns the gene CD40LG and autoimmune disease.