Intramacrophage Pathogens Research Articles

The interaction between Mycobacterium and the macrophage analyzed by two-dimensional polyacrylamide gel electrophoresis.

The intramacrophage pathogen Mycobacterium avium resides in a vacuole which displays unusual fusion characteristics, expressed as both a failure to mature into phagolysosomes and a continued access to the early recycling pathway. In contrast, compartments containing inert IgG-opsonized latex beads mature to phagolysosomes. Techniques were developed for the isolation of these particle-containing phagosomes from macrophages to facilitate analysis of phagosomal constituents by electrophoresis and autoradiography. Metabolic labeling of macrophages followed by phagosome isolation and two-dimensional polyacrylamide gel electrophoresis revealed only minor differences in the protein profiles between the M. avium and IgG-bead phagosomes despite the marked differences in the fusigenicity of the respective vacuoles. Pulse-chase labeling experiments revealed greater differences in the accessibility of Mycobacterium avium and IgG-bead phagosomes to newly synthesized proteins. These phagosome isolation techniques were extended to analyze the protein synthesis profile of intracellular M. avium for comparison with bacteria that were metabolically labeled in broth culture. Not surprisingly, the majority of polypeptides in the bacilli were common to both growth conditions. However, despite these similarities, intracellular M. avium express several unique proteins, most notably one abundant protein with a molecular weight of 51 kDa. In addition, the bacteria manifest a restricted set of proteins expressed while in stasis shortly after infection.

Leishmania Phagolysosome: Drug Trafficking and Protein Sorting Across the Compartment

Survival or destruction of intramacrophage pathogen Leishmania depends in part on modulation of their host cell phagosome, capabilities of the infected macrophages to present parasite antigen to the host's immune system. Macrophages house these parasites as amastigotes in the acidic phagolysosomal compartment. Leishmania phagolysosome is the potential site for processing and presentation of its antigen as well as being the target site for chemotherapy in leishmaniasis. It is thought that the parasites are killed from macrophage activation by lymphokines secreted from either helper T1 cells or CD8+ T cells. Characterization of both the host and parasite molecules in the compartment in the context of biogenesis of Leishmania-phagolysosome and processing of the parasite antigen by this compartment are discussed. Trafficking of different drugs and new agents through this compartment and their role in chemotherapy and necessity of developing new drug carrier are also stressed.

Expression of the natural resistance gene Lsh in resident liver macrophages.

Innate resistance and susceptibility to Leishmania donovani infection in mice is controlled by a single gene (Lsh) thought to be identical to the genes Ity and Bcg which control the early response to Salmonella typhimurium and Mycobacterium bovis infections, respectively. In the present study, three new aspects of Lsh gene activity were demonstrated. First, it was shown that liver macrophages continue to express Lsh gene activity in vitro after their extraction from mice infected in vivo, although 2 days of infection were required before the resistant phenotype was expressed. Second, detailed examination of early growth of the parasite and tritiated thymidine labeling of the parasites indicated that this delay in expression of the resistant phenotype also occurred in vivo. Third, the expression of resistance was unaltered by the effects of lethal irradiation but could be selectively enhanced by prior treatment with suitable doses of S. typhimurium lipopolysaccharide or L. donovani membranes. These results suggest that the resistance mechanism may be expressed by resident liver macrophages after their interaction with parasite-derived material. The relevance of these findings to the other intramacrophage pathogens is discussed.