Mac-1⁺ cells are the predominant subset in the early hepatic lesions of mice infected with Francisella tularensis

The cell composition of early hepatic lesions of experimental murine tularemia has not been characterized with specific markers. The appearance of multiple granulomatous-necrotic lesions in the liver correlates with a marked increase in the levels of serum alanine transferase and lactate dehydrogenase. Francisella tularensis, detected by specific antibodies, can be first noted by day 1 and becomes associated with the lesions by 5 days postinoculation. These lesions become necrotic, with some evidence of in situ apoptosis. The lesions do not contain B, T, or NK cells. Rather, the lesions are largely composed of two subpopnlations of Mac-1⁺ cells that are associated with the bacteria. Gr-1⁺ Mac-1⁺ immature myeloid cells and major histocompatibility complex class II-positive (MHC-II⁺) Mac-1 ⁺ macrophages were the most abundant cell phenotypes found in the granuloma and are likely major contributors in controlling the infection in its early stages. Our findings have shown that there is an early development of hepatic lesions where F. tularensis colocalizes with both Gr-1⁺ Mac-1⁺ and MHC-II⁺ Mac-1⁺ cells.