A comparison of the inhibition of leucocyte migration and monocyte spreading as in vitro assays for tuberculin hypersensitivity in man.

The ability of leucocyte migration inhibition and monocyte spreading inhibition test to detect tuberculin hypersensitivity was compared in the same twelve Mantoux-negative and fifteen Mantoux-positive persons. Tuberculin hypersensitivity expressed in vitro as migration or spreading inhibition, induced by 100 mug of PPD/ml, was assessed after 2 and 24, or 4 and 20 hr of incubation. A significant difference was found between negative and positive persons by migration inhibition at the early interval and by spreading inhibition at both intervals. When the two tests were compared on the basis of individual results, monocyte spreading inhibition appeared more discriminating (fewer results in the group of positive persons overlapped with those found among negative persons). Results of the monocyte spreading inhibition test correlated well with cutaneous reactions at both incubation intervals, while with migration inhibition the correlation was not so well expressed at either interval. Furthermore, a given change in skin reactivity of tuberculin-positive persons was reflected better in spreading inhibition than in migration inhibition indices. We conclude that the method of monocyte spreading inhibition compares favourably with the method of leucocyte migration inhibition, and it seems to be a suitable in vitro test for detection of tuberculin hypersensitivity in man.