Leishmania-Induced Inhibition of Macrophage Antigen Presentation Analyzed at the Single-Cell Level

Abstract

A number of studies have previously examined the capacity of intracellular Leishmania parasites to modulate the capacity of macrophages to process and present Ags to MHC class II-restricted CD4+ T cells. However, the bulk culture approaches used for assessing T cell activation make interpretation of some of these studies difficult. To gain a more precise understanding of the interaction between Leishmania-infected macrophages and effector T cells, we have analyzed various parameters of T cell activation in individual macrophage-T cell conjugates. Leishmania-infected macrophages efficiently stimulate Ag-independent as well as Ag-dependent, TCR-mediated capping of cortical F-actin in DO.11 T cells. However, infected macrophages are less efficient at promoting the sustained TCR signaling necessary for reorientation of the T cell microtubule organizing center and for IFN-γ production. A reduced ability to activate these T cell responses was not due to altered levels of surface-expressed MHC class II-peptide complexes. This study represents the first direct single-cell analysis of the impact of intracellular infection on the interaction of macrophages with T cells and serves to emphasize the subtle influence Leishmania has on APC function.

The fate of heterologous CD4+ T cells during Leishmania donovani infection

“…First, it is possible that these memory DO11 cells are triggered into proliferation by renewed presentation of OVA in L. donovani-infected mice. Although L. donovani-infected mice have severe impairment of APC function [17,[30][31][32], the abundance of MHC class II expression in L. donovani-infected mice [33] coupled with the lesser requirements of memory CD4 + T cells for costimulation [34] makes this possibility difficult to rule out at this time. Alternatively, proliferation of DO11 cells may be triggered by TCR-independent cytokine-mediated mechanisms.…”

Leishmania donovani Affects Antigen Presentation of Macrophage by Disrupting Lipid Rafts

“…These peptide-pulsed P388D1(N) and P388D1(I) cells were used as APCs to drive peptide-specific T cell hybridomas. Normal M were pulsed with HEL (1 mg/ml) for 4 h, then washed and kept for another 24 h. Finally, cells were stained with FITC-labeled-C4H3, and the extent of peptide-MHC complex present on the cell surface was determined by FACS analysis (15).…”

“…The Ag-presenting ability of splenic M infected with LD was investigated with increasing concentrations of R [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] . Because our study is concerned with cell surface phenomena associated with Ag presentation, we have used the processing-independent peptide sequence R 12-26 to drive T cells (14).…”

“…The M were then incubated further for 6,12,24,36,48,60, and 72 h to determine their ability to support intracellular parasite replication (54). The splenic M and P388D1, infected or not, were used as APCs to drive T cell hybridomas in the presence or the absence of R [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] (55).…”

“…Leishmania-infected M are unable to present even processing-independent peptide sequences to T cell hybridoma, and this inability is not due to defective MHC expression (14). Recent studies show that Leishmania-infected M efficiently stimulate Ag-independent and Ag-dependent TCR-mediated capping of F-actin in T cells (15). Infected M are less efficient at promoting the sustained T cell signaling events, but this is not due to altered levels of surfaceexpressed peptide-MHC complexes (15).…”