The relation between cutaneous blood flow and cell content in the tuberculin reaction.

The relationship of velocity of blood flow to density and microanatomical distribution of inflammatory cells in the dermis was studied in 20 human tuberculin tests. Most positive reactions showed maximal blood flow velocities (measured as red blood cell (RBC) flux) at the centre of the reaction, but the two most intense responses showed 'central relative slowing' (CRS) with higher RBC flux at the periphery. Two of the four clinically negative reactions showed a considerable acceleration of blood flow, but the other two showed no such acceleration. The packing density of lymphocytes/monocytes in the perivascular zone was greater in the stronger positives than in the weaker reactions. The density of cells in the intervening dermis was markedly lower than in the foci: the lesions with CRS had the highest density of cells in the diffuse infiltrate of the reticular dermis. At the centre of the reaction, blood flow velocity was generally related to density of cellular infiltrate, except in those with CRS, which had a disproportionately lower blood flow velocity. The finding that the circulatory adaptation to a delayed hypersensitivity reaction can be inadequate may explain the dermal acidosis previously observed in intense skin test reactions, and may be the underlying mechanism of necrosis in hypersensitivity reactions.