Localization of major histocompatibility complex class II molecules in phagolysosomes of murine macrophages infected with Leishmania amazonensis

Abstract

Leishmania-infected macrophages are potential antigen-presenting cells for CD4+ T lymphocytes, which recognize parasite antigens bound to major histocompatibility complex class II molecules (Ia). However, the intracellular sites where Ia and antigens may interact are far from clear, since parasites grow within the modified lysosomal compartment of the host cell, whereas Ta molecules seem to be targeted to endosomes. To address this question, the expression and fate of Ta molecules were studied by immunocytochemistry in Leishmania amazonensis-infected murine macrophages stimulated with gamma interferon. In uninfected macrophages, la molecules were localized on the plasma membrane and in perinuclear vesicles, but they underwent a dramatic redistribution after infection, since most of the intracellular staining was then associated with the periphery of the parasitophorous vacuoles (p.v.) and quite often polarized towards amastigote-binding sites. The Ii invariant chain, which is transiently associated with Ta during their intracellular transport, although well expressed in infected macrophages, apparently did not reach the p.v. Similar findings were observed with macrophages from mice either resistant or highly susceptible to Leishmania infection. In order to determine the origin of p.v.-associated Ta, the fate of plasma membrane, endosomal, and lysosomal markers, detected with specific antibodies, was determined after infection. At 48 h after infection, p.v. was found to exhibit a membrane composition typical of mature lysosomes. Overall, these data suggest that (i) la located in p.v. originate from secondary lysosomes involved in the biogenesis of this compartment or circulate in several endocytic organelles, including lysosomes and (ii) p.v. could play a role in antigen processing and presentation. Alternatively, the presence of high amounts of Ia in p.v. could be due to a Leishmania-induced mechanism by means of which this organism may evade the immune response.

Down-regulation of MHC class II molecules and inability to up-regulate class I molecules in murine macrophages after infection withToxoplasma gondii

“…After incubation for 3 days at 37ЊC and 5% CO 2 in saturated humidity, 50% medium was exchanged and after an additional 3 days cells were cultured for 24 h in medium devoid of M-CSF. Before infection, the number of adherent BMM per coverslip was determined as described [18]. Briefly, cells were lysed in 1% cethyltrimethylammonium bromide, 0·05% naphthol blue black in 0·1 M citric acid before counting macrophage nuclei in a haemocytometer.…”

Phagocytic processing of antigens for presentation by class II major histocompatibility complex molecules

“…This may be partly explained by the fact that content and traf®c of phagosomal proteins varies with the type of particle ingested. Several reports have identi®ed MHC molecules in phagolysosomes, largely by immunoelectron microscopy (Antoine et al, 1991;Lang and Kaye, 1991;Harding and Geuze, 1992). Clemens and Horwitz demonstrated low levels of MHC molecules on 1-and 5-day-old latex bead phagosomes in human mononuclear cells by electron microscopy, although these studies did not include earlier time points.…”

Immune Responses of IL‐4, IL‐5, IL‐6 Deficient Mice

“…L. major, a fiagellated protozoan parasite, is peculiar in that it lives and replicates in phagolysosomes of macrophages, a compartment in which MHC class II molecules colocalize (Antoine et al 1991). The infection of mice from different genetic backgrounds with L major leads to one of two dramatically different patterns of disease.…”