Natural killer cell function and expression of beta 7 integrin in psoriatic arthritis

To examine the cytotoxic activity of natural killer (NK) cells from peripheral blood (PB) and synovial fluid (SF) of patients with psoriatic arthritis (PsA). The influence of selected inflammatory mediators on the cytolytic function and integrin expression of NK cells was also studied.

Paired samples of PB and SF lymphocytes (PBL and SFL) were obtained from 8 patients with PsA for comparison of NK activity between PBL and SFL. In 6 patients the phenotype of NK cells was determined by flow cytometry using monoclonal antibodies (Mab) to natural killer associated antigen (NKH-1) and the beta 7 integrin, HML-1 (human mucosal lymphocyte adhesion molecule).

NK activity of PB samples was significantly greater than paired SF (p = 0.015). SF NK activity was enhanced by overnight culture with interleukin 2 (IL-2) (p < 0.05). A trend towards reduction of NK activity by prostaglandin E2 (PGE2) was noted (p = 0.06) whereas interleukin 6 (IL-6) and indomethacin had no significant effect. NK activity did not correlate with the percentage of NK cells in PB or SF. However, all SF samples contained a greater proportion of monocytes than PB samples. The expression of HML-1 on NK cells correlated with expression HML-1 on CD3+ cells (r = 0.82) and was greater in SF than PB in PsA and RA patients. Effects of IL-2 on HML-1 expression by NK cells were variable in the 3 patients studied.

In PsA, HML-1 is an activation marker on NK cells. IL-2 expands or maintains the population of HML-1/NKH1 positive cells and increases NK cytolytic activity. However, cytolytic activity of activated NK cells may be inhibited by monocyte derived PGE2.