Relationship of tryptophan degradation with immune activity in rheumatoid arthritis

RA is a systemic, inflammatory, autoimmune disease with completely unknown etiology. It?s clinical symptoms can be observed in different ways ranging from mild to severe symptoms. The increase in IFN-? and TNF-? levels depending on immune activation and inflammation, increases both expression of indolamine 2,3-dioxygenase and neopterin synthesis in monocytes, macrophages and dendritic cells.In this study, we measured the levels of tryptophan and kynurenine by using HPLC technique, and the levels of serum neopterin and TNF-? by using ELISA technique in 32 patients diagnosed as RA based on ARA criteria and 20 healthy subjects. The ratio of kynurenine to tryptophan is evaluated as a measure of tryptophan degradation and indolamine 2,3-dioxygenase enzyme activity. We evaluated the effects of age, gender, duration of disease and methotrexat treatment on the measured parameters.There was no significant difference between the patient and healthy subjects in terms of serum tryptophan , kynurenine, neopterin and TNF-? levels (p>0.05). The CRP, ESR and RF levels of patients with rheumatoid arthritis were higher than those of healthy subjects (p<0.001). In spite of higher values in RA patients, IDO activity did not reach significant level (p>0.05). It was observed increase in neopterin levels and IDO activity with age in RA patients (r=0.401 p<0.04 for neopterin and r=0.435 p<0.02 for IDO activity). Compared with patients having rheumatoid arthritis less than 5 years, patients having rheumatoid arthritis for more than 5 years had significantly higher neopterin levels (p<0,05) and these levels positively correlated with kynurenine (r=0.537 p<0.02) and ESR (r=0.495 p<0.03).There was no statistically significant difference between the patients treated with methotrexat and without methotrexat in terms of measured parameters, but neopterin levels positively correlated with kynurenine levels and IDO activity in patients treated with methotrexat (r=0.511, p<0.03 for kynurenine and r=0.505, p<0.04 for IDO Activity).Key Words: Indolamine 2,3?Dioxygenase (IDO) , Immune System, Rheumatoid Arthritis , Neopterin, Tumor Necrosis Factor ? Alfa ( TNF ? ? )