ULTRACYTOCHEMICAL STUDY OF MULTIPLE-DOSE EFFECT OF MONASTRAL BLUE UPTAKE BY EQUINE PULMONARY INTRAVASCULAR MACROPHAGES (PIMS)

The pulmonary intravascular macrophages (PIMs) of the ponies possess a ll the characteristics of a fully differentiated resident macrophage, which forms adhesive plaques with the capillary-endothelial cells. In addition, it has a unique surface coat which does not conform to the c oncept of a carbohydrate rich membrane bound glycocalyx generally asso ciated with macrophages. We studied the responses of these cells espec ially in the context of its globular surface coat to multiple doses of monastral blue (MB), a copper tracer substance. The ponies were treat ed with three doses of MB intravenously: 0.2 ml/kg body weight on day 0, 0.1 ml/kg at 48 h and a 0.05 ml/kg at 96 h after the first dose. Th e examination of lung tissue at the ultrastructural level revealed int ernalization of MB following complexing with the surface coat globules along the entire cell surface. The cell surface was extensively ruffl ed in the form of several lamellipods. The MB-globule complex was inte rnalized mostly at the coated pits whereas concurrent internalization of nascent globules of the coat took place at the ruffled surface. In the former, the internalized material was seen in small, medium and la rge phagolysosomes which stained intensely for acid phosphatase, where as in latter case enzyme activity was entirely absent in all the nasce nt globules carrying endosomes. Simultaneously there was hypertrophy o f the Golgi complex, which showed intense staining for acid phosphatas e. Relative to the Golgi response, acid phosphatase-positive tubular l ysosomes in close association with extensive bundles of microtubules w ere conspicuous, thus adding to the battery of cell organelles of secr etory pathway. These results indicate that PIMs have an enormous poten tial for the uptake of exogenous MB pigment, a capacity which is perha ps dependent upon the presence of globular surface coat.