Rheumatoid arthritis is the most common, chronic inflammatory joint disease, which etiology still remains unknown. The diagnosis of this disease, despite the set diagnostic criteria, is still problematic, especially in the early stage. Promising laboratory parameter, which beside high specificity and peculiarity, has also huge prognostic value, are antibodies against citrullinated proteins ACPA. They can occur many years before the first symptoms of the disease onset, moreover are related with the presence of a shared epitope – SE, which predisposes to development of rheumatoid arthritis. The appearance of anticitullin antibodies results from excessive expression of citrullinated proteins in inflammatory tissues. Therefore, the identification of deiminated antigens, their localization and examination of functional changes induced by citrulination recently became an object of intensive research. High homology between human citrullinated α-enolase, which induces the production of antibodies, and bacterial enolase has drawn attention to the infectious aspect of the RA etiology. Porphyromonas gingivalis deserves special interest, the only microbe, which produces peptidylarginin deiminase – the enzyme responsible for citrulination in eucariot. The data shown in reviewed studies allow us better understanding of changes in the course of the disease and promise earlier diagnosis and implementation of treatment in the future.