Natural killer cell activity and its relationship with disease activity in rheumatoid arthritis patients

The aim of this study was to explore the relationship between natural killer cell activity (NKA) and disease activity of rheumatoid arthritis (RA). We retrospectively reviewed 259 patients' data including RA markers associated with disease activity and NKA measured by a blood NKA test. Patients were divided into two groups based on their NKA levels, a low NKA group (NKA < 100 pg/mL) and a high NKA group (NKA 100-250 pg/mL). The low NKA group exhibited heightened RA characteristics, including increased seropositivity, anti-cyclic citrullinated peptide (anti-CCP) antibodies, erythrocyte sedimentation rate (ESR), 28-joint disease activity score, tender joints, visual analog scale (VAS), and TNF-α antagonist usage. A negative correlation was observed between NKA and RA severity metrics, including rheumatoid factor (RF), anti-CCP antibodies, ESR, C-reactive protein, tender and swollen joints, and VAS scores. Logistic regression analysis indicated that factors such as seropositivity, elevated RF and anti-CCP antibodies, increased tender and swollen joints, higher VAS scores, and the employment of biological agents were linked with higher chances of belonging to the lower NKA group. Comparable trends were found within the seropositive RA patient subset. Our findings highlight a significant link between diminished NKA levels and exacerbated RA symptoms.