RELATIONSHIP OF ACID-PHOSPHATASE-ACTIVITY TO ULTRASTRUCTURAL FEATURESIN MICE INOCULATED WITH MYCOBACTERIUM-PARATUBERCULOSIS

Macrophage activation, measured as increased acid phosphatase (AcPase) -positive areas by image analysis, and ultrastructural features were e xamined in granulomatous mycobacterial lesions of mice innately suscep tible (BALB/c mice; Bcg(s)) and innately resistant (C3H/HeJ mice; Bcg( r)) to Mycobacterium paratuberculosis strain ATCC 19698. In the liver and spleen of BALB/c mice 3 weeks after intraperitoneal inoculation wi th M. paratuberculosis, AcPase activity detected in epithelioid cell n odules was high; it had decreased, however, in the liver and spleen af ter a further 3 and 6 weeks, respectively. In C3H/HeJ mice, the size o f epithelioid cell nodules in the liver and spleen was smaller than in BALB/c mice, and infiltrating macrophages, which had increased by wee k 9 after inoculation, showed high AcPase activity. Ultrastructurally, by week 32 in BALB/c mice, small phagolysosomes (SPLs) had greatly in creased in number in the epithelioid cells. These SPLs contained a few AcPase-positive areas and a small number of bacteria, most of which w ere surrounded by an electron-translucent space (or electron-transpare nt zone [ETZ]). In contrast, only a few SPLs were observed in C3H/HeJ mice at week 32; in the liver and spleen, large phagolysosomes (LPLs) showed high AcPase activity and contained many degenerated bacteria, w hich also had an ETZ. These results suggest that the enzymatic and ult rastructural differences in phagolysosomes between BALB/c mice and C3H /HeJ mice reflect the susceptibility of these mouse strains to M. para tuberculosis. (C) 1996 W.B. Saunders Company Limited