Macrophage subsets harbouring Leishmania donovani in spleens of infected BALB/c mice: localization and characterization

The purpose of the current study was to characterize parasite-containing ce lls located in spleens of BALB/c mice infected with Leishmania donovani. In particular, expression of MHC class II molecules by these cells was examin ed to determine whether they could potentially act as cells capable of immu nostimulating Leishmania-reactive CD4(+) T lymphocytes. To this end, an imm unohistological analysis of spleens taken at various time points after infe ction was undertaken. Using this approach, we observed, in the red pulp, th e formation of small cellular infliltrates containing heavily infected macr ophages that could be stained with the monoclonal antibodies MOMA-2 and FA/ 11. All of them expressed high levels of MHC class II molecules. Parasites were also detected in the white pulp, especially in MOMA-2(+), FA/11(+) and MHC class II+ macrophages of the periarteriolar lymphocyte sheath and in M OMA-2(+) marginal zone macrophages. Infected cells were further characteriz ed by fluorescence microscopy after their enrichment by adherence. All infe cted mononuclear cells recovered by this procedure could be stained with MO MA-2 and FA/11 and thus very probably belonged to the mononuclear phagocyte lineage. Furthermore, all of them strongly expressed both MHC class II as well as H-2M molecules, regardless of the time points after infection. Anal ysis of the parasitophorous vacuoles (PV) by confocal microscopy showed tha t these compartments were surrounded by a membrane enriched in lysosomal gl ycoproteins lamp-1 and lamp-2, in macrosialin (a membrane protein of prelys osomes recognized by FA/11) and in MOMA-2 antigen. About 80% of the PV also had MHC class II and H-2M molecules on their membrane. Altogether, these d ata indicate that in the spleens of L. donovani-infected mice, a high perce ntage of amastigotes are located in macrophages expressing MHC class II mol ecules and that they live in PV exhibiting properties similar to those of P V detected in mouse bone marrow-derived macrophages exposed to a low dose o f interferon gamma (IFN-gamma) and infected in vitro.