Natural killer cell activity and frequency of killer cell immunoglobulin‐like receptors in children with different forms of juvenile idiopathic arthritis

Background Juvenile idiopathic arthritis ( JIA ) has three major onset types with widely varying clinical features: systemic, polyarticular and pauciarticular. We assessed natural killer ( NK ) cell function and killer cell immunoglobulin‐like receptor ( KIR ) genotypes in patients with different JIA subtypes. Methods Peripheral blood samples from 72 children with active JIA (systemic, 25; polyarticular, 24; pauciarticular, 23) and 25 controls were used for flow cytometric assessments of NK cell count, cytotoxicity, perforin, granzyme B, interferon ( IFN )‐γ and tumour necrosis factor ( TNF )‐α. Samples from 220 children with JIA (systemic, 84; polyarticular, 72; pauciarticular, 64) and 150 controls were used for KIR 2 DS 2 , KIR 2 DS 4 , KIR 3 DS 1 , KIR 2 DL 1 , KIR 2 DL 2 , KIR 2 DL 3 and KIR 3 DL 1 typing by polymerase chain reaction with sequence‐specific oligonucleotide probes. Results Compared with the controls, the patients with systemic JIA showed lower NK cell counts, cytotoxicity and perforin and granzyme B expression (p < 0.05), while the patients with pauci‐ and polyarticular JIA showed higher perforin and granzyme B expression (p < 0.05). NK cells produced higher level of TNF ‐α while lower level of IFN ‐γ in the pauci‐ and polyarticular JIA groups than in the systemic JIA group (p < 0.05). No significant differences in KIR gene frequencies were found between the JIA subgroups and healthy controls, except for the positive frequency and locus frequency of KIR 2 DS 4 , which were lower in the systemic JIA group. Conclusions Compared with poly‐ and pauciarticular JIA , systemic JIA is associated with decreased NK cell function, more IFN ‐γ and less TNF ‐α secretion of NK cell and lower KIR 2 DS 4 frequency.