Recently, Systemic lupus erythematosus (SLE) was considered as one of the autoimmune diseases that the genetic and environmental factors contributed in the disease etiological profile. According to the environmental factors, infectious agents have been concluded to have a role in the etiology and pathogenesis of SLE. Chlamydia pneumoniae and Mycoplasma pneumoniae are among these infectious agents that have been suggested to be involved in the etiology of SLE. Accordingly, the current study was designed to assess the anti-C. pneumoniae and anti-M. pneumoniae IgG antibody status by enzyme linked immunosorbent assay (ELISA) in the sera of 64 Iraqi SLE females' patients and 32 Iraqi healthy females as controls. The patients' group were distributed into two equal subgroups (32 cases in each group); arthritis and nephritis. The findings revealed that 25% of the total SLE patient’s sera were positive for anti-C. pneumoniae IgG antibody, while such antibody was not detected in controls. The difference was significant (p = 9.8 x 10-4) and associated with OR of 22.1. With respect to M. pneumoniae, 67.7% of SLE patient’s sera were positive for anti-M. pneumoniae IgG antibody while none of control’s sera was positive. The difference was significant (p = 4.0 x 10-9) and the associated OR was 141.1. For both pathogens, a similar profile was observed in arthritis and nephritis SLE patients. These findings may suggest that C. pneumoniae and M. pneumoniae are two pathogens involved in etiology and pathogenesis of SLE.
