Natural killer cells in viral arthritis

Changes in natural killer (NK) cell activity were studied in patients with polyarthritis associated with rubella or Ross River virus infections. In 30 of 32 Ross River virus patients, peripheral NK cell activity was depressed at some stage of the disease but returned to normal levels as patients recovered from arthritic symptoms. Similar changes did not occur in rubella patients and no difference was found between changes in peripheral NK activity and serum interferon (IFN) levels in rubella patients with arthritis and those without. Neither the peak of NK cell activity in peripheral blood lymphocytes (PBL) recovered early in Ross River virus and rubella infections, nor the depression of NK cell activity late in Ross River virus infections could be correlated with changes in serum IFN levels. The decrease in PBL-NK cell activity in epidemic polyarthritis (EPA) patients could not be attributed solely to loss of NK cells from the peripheral circulation because limiting-cell-dilution (LCD) analyses indicated changes in peripheral NK cell activity were due to changes in both the number and lytic activity of NK cells. Despite the association between HLA-DR7 and EPA no differences were found in levels of peripheral NK cell activity in DR7+ and DR7- EPA patients. The demonstration that peripheral NK cells could kill autologous synovial cells suggested that NK cells in joints of EPA patients may contribute to the arthritis associated with Ross River virus infection.