Phagocytic potential of macrophages from within delayed hypersensitivity-mediated granulomata.

The phagocytic potential of macrophages from within granulomas associated with delayed hypersensitivity was studied in guinea-pigs sensitised with FCA and challenged either with PPD or live M. tuberculosis. The results show that FCA treatment induces a 30 percent increase in phagocytosis of IgG coated erythrocytes by macrophages which migrate into a foreign body granuloma. PPD treatment enhances this index to about 70 per cent. When live M. tuberculosis was used as antigen the phagocytic index of macrophages from lesions induced in sensitised animals was about 50 per cent. higher than in controls. The increase in phagocytosis by macrophages was maximal at 4 days and decreased 8 and 16 days after challenge, in both sensitised and non-sensitised animals. The results show that in granulomas associated with delayed hypersensitivity, macrophages have a transitory increase in their phagocytic activity. Later the older cells in the centre of the granuloma lose this property, thereby facilitating antigen persistence and chronicity.