Major histocompatibility complex class I and II expression on macrophages containing a virulent strain of Brucella abortus measured using green fluorescent protein-expressing brucellae and flow cytometry

• Published in: FEMS immunology and medical microbiology Vol. 33; no. 3; pp. 191 - 200
• Main Authors: Murphy, E., Robertson, G.T., Parent, M., Hagius, S.D., Roop, R.M., Elzer, P.H., Baldwin, C.L.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 12-07-2002; Blackwell
• Subjects: Animals; Bacterial diseases; Bacteriology; Biological and medical sciences; Brucella; Brucella abortus - genetics; Brucella abortus - metabolism; Brucella abortus - pathogenicity; Brucellosis - microbiology; Cell Line; Colony Count, Microbial; Experimental bacterial diseases and models; Flow Cytometry; Fundamental and applied biological sciences. Psychology; Green fluorescent protein; Green Fluorescent Proteins; Histocompatibility Antigens Class I - metabolism; Histocompatibility Antigens Class II - metabolism; Infectious diseases; Intracellular bacterium; Luminescent Proteins - genetics; Luminescent Proteins - metabolism; Macrophage; Macrophages, Peritoneal - metabolism; Macrophages, Peritoneal - microbiology; Medical sciences; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Microbiology; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Virulence; Intracellular bacterium; Green fluorescent protein; Macrophage; Animal model; Immune response; Major histocompatibility system; Rodentia; Class II histocompatibility antigen; Host agent relation; Brucella abortus; Gene expression; Infection; Vertebrata; Mammalia; Brucellaceae; Mouse; Bacteriosis; Virulent strain; Bacteria; Brucellosis; Intracellular; Class I histocompatibility antigen
• ISSN: 0928-8244; 1574-695X
• DOI: 10.1111/j.1574-695X.2002.tb00590.x

Abstract
Immune responses appropriate for control of an intracellular pathogen are generated in mice infected with Brucella abortus, shown by the ability of T cells to adoptively transfer resistance to naive mice. The infection nevertheless persists for months. It was hypothesized that one factor in maintaining the infection despite the presence of immune T cells was suboptimal expression of major histocompatibility complex (MHC) molecules on macrophages containing brucellae. This would allow B. abortus to elude detection by the host's immune system. To test this, B. abortus organisms expressing green fluorescent protein (GFP-Brucella) were constructed and three-color flow cytometry used to evaluate MHC expression on macrophages following in vitro or in vivo infection. When infected in vitro, the levels of MHC class I and class II expression on J774 macrophages containing GFP-Brucella were the same or higher than on macrophages without GFP-Brucella in the same cultures. Similarly, the MHC expression was higher on GFP+ peritoneal exudate cells following infection or phagocytosis of heat-killed GFP-Brucella than it was on uninfected peritoneal exudate cells. Following in vivo infection of mice the level of MHC class I and II expression on GFP+ cells in their spleens (the main site of infection) also tended to be as high as or higher than that on the GFP-negative cells. The only in vivo GFP+ cells that showed a decreased MHC expression was a population of splenic Mac1+ cells recovered from interferon-γ gene-disrupted mice at the time of their death due to an overwhelming number of bacteria per spleen. Overall, it was concluded that decreased MHC expression is not a general principle associated with brucella infection of macrophages and thus not likely to contribute to maintenance of the chronic infection.