There is an increasing need for novel biomarkers that enable better diagnostic and prognostic stratification of patients with suspected infection. A proprotein convertase enzyme FURIN is upregulated upon immune cell activation, and it promotes infectivity by cleaving and activating pathogens. In this study, we determined FURIN levels in plasma using ELISA from 537 patients that were admitted to emergency room with suspected infection. Patients were sorted to high-and low-level FURIN groups with a cut-off level of 370 pg/ml. The study cohort included five diagnostic groups: Group 1, no systemic inflammatory response syndrome (SIRS, n = 59 patients); Group 2, bacterial infection without SIRS (n = 67); Group 3, SIRS, but no bacterial infection (n = 308); Group 4, sepsis without organ failure (n = 308); and Group 5, severe sepsis (n = 49). Statistically significant associations were not found between the plasma level of FURIN and the prevalence of sepsis (P = 0.957), diagnostic group of a patient (P = 0.737) or the bacteria in blood culture (P = 0.499). Additionally, the concentration of FURIN did not predict the severity or case fatality of the infectious disease. However, statistically significant associations were found between high plasma level of FURIN and diagnosed rheumatic disease (P < 0.001) as well as with the prevalence of non-smokers (P = 0.034). Thus, albeit the plasma level of FURIN does not predict the severity of infectious disease, it may be of use in the diagnostics of autoimmune diseases.

FURIN is a proprotein convertase enzyme that inhibits the pro-inflammatory function of T cells and myeloid cells. Previously, elevated FURIN expression levels have been reported in immune-mediated diseases, such as primary Sjögren's syndrome. Here, we investigated the levels of FURIN in peripheral blood (PB) and synovial fluid (SF) leukocytes from patients with rheumatoid arthritis (RA). Methods FURIN mRNA expression in PB and SF cells was determined by qRT-PCR and FURIN plasma levels were measured using ELISA. Associations between FURIN levels and demographic and clinical characteristics of the patients were determined. Results FURIN levels were significantly elevated in PB and SF mononuclear cells, T cells and monocytes from RA patients when compared to healthy controls. High FURIN levels were significantly associated with the prevailing prednisolone treatment, higher prednisolone doses as well as increased CRP levels and Health Assessment Questionnaire (HAQ) values. Conclusion FURIN is significantly upregulated in RA PB and SF leukocytes, suggesting that FURIN may have a role in the pathogenesis of RA. In addition, our results suggest that elevated FURIN expression is associated with the indicators of more severe RA.