Objectives: To assess natural killer (NK) and cytotoxic functions in patients with systemic-onset juvenile rheumatoid arthrithis (soJRA) complicated by macrophage activation syndrome (MAS).
Methods: NK cells (CD56+/TCRalphabeta-), NK T cells (CD56+/TCRalphabeta+) and CD8+ cells were assessed for perforin expression by flow cytometry. NK cytotoxic activity was measured after coincubation of mononuclear cells with an NK-sensitive K562 cell line.
Results: Two major patterns of immunologic abnormalities were detected. Four of 7 patients had decreased NK activity, low NK cell numbers, and mildly increased levels of perforin expression in CD8+ and CD56+ cytotoxic cells. Three remaining patients with MAS, however, had decreased NK activity associated with low levels of perforin expression in all cytotoxic cell populations, a pattern indistinguishable from that in carriers of perforin-deficient familial hemophagocytic lymphohistiocytosis. Remarkably, two of these patients had previous episodes of MAS.
Conclusions: NK dysfunction is an immunologic abnormality common to both familial hemophagocytic lymphohistiocytosis and MAS of soJRA. The extent of NK cell abnormalities in soJRA needs to be further investigated.