Natural killer (NK) cell activity and reversal reaction in leprosy.

Two studies were conducted to assess natural killer (NK) cell activity in leprosy patients and healthy Ethiopian controls. The first study tested 26 untreated leprosy patients across the spectrum of the disease. It was found that lepromatous leprosy and all untreated, nonreactional patients had lower NK activity than healthy controls. However, patients presenting with reversal reaction (RR) had NK activity within the normal range. Heterogeneity was particularly marked in the NK activity of borderline patients. In the second study, NK cell activity was assessed in treated borderline tuberculoid leprosy (BT) patients. There were 30 patients with a history of RR and 27 BT patients without such a history (NR). All patients had had at least 3 years of dapsone treatment and 6 months of multidrug therapy. There were 26 control subjects. NK activity was higher in controls than in patients only at one effector:target (E:T) ratio tested, but NK cells from the BT patient group appeared to be more "aggressive" in that there was significantly (p less than 0.001) less reduction of activity with dilution of effector cells. There were no significant differences in NK activity between RR and NR patients. The NK activity of NR patients was positively correlated with the size of induration of the lepromin response. We conclude that higher NK activity in acute RR would appear to be a consequence rather than a cause of reversal reactions.