A SEQUENTIAL STUDY OF THE BOVINE TUBERCULIN REACTION

The sequential histopathological and immunocytochemical changes that c haracterize the tuberculin reaction were studied in 13 cattle experime ntally sensitized to Mycobacterium bovis, and 14 cattle naturally infe cted with M. bovis. There were two distinct, temporally related patter ns of morphological change that were similar for both groups of cattle . The first phase, between 6 hr and 24 hr after the intradermal inject ion of purified protein derivative (PPD), was characterized by a periv ascular aggregation of WC1(+) gamma delta T cells and neutrophils and the presence of leucocytoclastic vasculitis within the papillary dermi s. The second phase of the reaction was characterized by increased num bers of infiltrating BoCD4(+) cells, BoCD8(+) cells and macrophages, a s well as an increase in expression of the interleukin-2 (IL-2) recept or and the ACT2 antigen. Macrophages were the most numerous infiltrati ng leucocytes between 24 hr and 72 hr after the intradermal injection of PPD. At 72 hr, the reaction was characterized by intense perivascul ar cuffing with BoCD4(+) cells, BoCD8(+) cells and macrophages; gamma delta T cells and neutrophils were a minor component of the reaction a nd leucocytoclastic vasculitis was no longer observed. No B cells were detected in the dermis throughout the period of study. The increase i n skin thickness was primarily because of inflammatory oedema that was contained within the area by a meshwork of fibrin deposited around th e collagen bundles of the reticular dermis.