['Rheumatoid arthritis (RA) is a chronic inflammatory disease that affects about 1% of the adult population and occurs twice as frequently among women than men. At present it is accepted that pathogenesis of RA is based on inflammatory response mediated by CD4(+) Th1 and Th17 lymphocytes. The most commonly applied model imitating RA is the collagen induced arthritis (CIA). A growing evidence shows that there is a correlation between microbial dysbiosis and human pathology which includes autoimmunity, allergic diseases, obesity, inflammatory bowel disease (IBD), metabolic syndrome.', 'Collagen induced arthritis was used to study influence of natural gut flora on course of rheumatoid arthritis.', 'Current work employing CIA model showed that partial depletion of natural gut flora with orally administered antibiotic Baytril (enrofloxacin) aggravates disease severity when compared to control mice. Observed partial depletion of both aerobic and anaerobic bacteria did not affect animal body weight. Additionally, in vitro study showed increased production of IFN-? and IL-17A and decreased release of IL-4 by axillary lymph node cells (ALNC) isolated from mice treated with antibiotic and induced CIA when compared to positive control. Furthermore, treatment with antibiotic prior to CIA induction results in augmented production of IFN-?, IL-17A and IL-6 by mesenteric lymph node cells (MLNC).'] Does partial depletion of natural gut flora by antibiotic aggravate collagen induced arthritis ( CIA ) in mice?