The MHC class II antigen presentation pathway in human monocytes differs by subset and is regulated by cytokines

Abstract

Monocytes play a critical role in the innate and adaptive immune systems, performing phagocytosis, presenting antigen, and producing cytokines. They are a heterogeneous population that has been divided in humans into classical, intermediate, and non-classical subsets, but the roles of these subsets are incompletely understood. In this study, we investigated the expression patterns of MHC class II (MHCII) and associated molecules and find that the intermediate monocytes express the highest levels of the MHC molecules, HLA-DR (tested in n = 30 samples), HLA-DP (n = 30), and HLA-DQ (n = 10). HLA-DM (n = 30), which catalyzes the peptide exchange on the MHC molecules, is also expressed at the highest levels in intermediate monocytes. To measure HLA-DM function, we measured levels of MHCII-bound CLIP (class II invariant chain peptide, n = 23), which is exchanged for other peptides by HLA-DM. We calculated CLIP:MHCII ratios to normalize CLIP levels to MHCII levels, and found that intermediate monocytes have the lowest CLIP:MHCII ratio. We isolated the different monocyte subsets (in a total of 7 samples) and analyzed their responses to selected cytokines as model of monocyte activation: two M1-polarizing cytokines (IFNγ, GM-CSF), an M2-polarizing cytokine (IL-4) and IL-10. Classical monocytes exhibit the largest increases in class II pathway expression in response to stimulatory cytokines (IFNγ, GM-CSF, IL-4). All three subsets decrease HLA-DR levels after IL-10 exposure. Our findings argue that intermediate monocytes are the most efficient constitutive antigen presenting subset, that classical monocytes are recruited into an antigen presentation role during inflammatory responses and that IL-10 negatively regulates this function across all subsets.

Treatment of advanced gastrointestinal cancer with genetically modified autologous mesenchymal stem cells: Results from the phase 1/2 TREAT‐ME‐1 trial

“…Human Leukocyte Antigen–antigen D Related (HLA‐DR) expression on monocytes was evaluated using flow cytometry. Since the Th1 cytokine IFNγ is known to enhance HLA‐DR expression on human monocytes, an increase in monocytic HLA‐DR expression was used as an indicator of Th1 shift . Further details on the assessment of immunological biomarkers can be found in the Supporting Information Appendix.…”

Astrocytes, the rising stars of the glioblastoma microenvironment

“…Similarly, IL‐10, an immunomodulatory cytokine with anti‐inflammatory properties, has also been shown to stimulate survival of GBM cells, notably via inhibition of the expression of proinflammatory mediators such as Class II MHC and IFN‐γ in vitro (Iyer & Cheng, ; Qi et al, ). Class II MHC is involved in the antigen‐presenting ability of monocytes while IFN‐γ has been shown to induce the synthesis of IL‐6 to support the immune eradication of GBM cell lines in vitro (Hotfilder et al, ; Lee et al, ; Yin et al, ). In addition, STAT‐3—another factor found up‐regulated in reactive astrocytes (Priego et al, )—plays an essential role in inducing angiogenesis, immunosuppression, and tumor invasion (Kim, Patel, Ruzevick, Jackson, & Lim, ).…”

“…Both local (i.e., gap junctions) and distant (i.e., cytokines and EVs) roles of TAAs should be exploited. Based on this article, TAAS‐produced IL‐6 appears to be at the crossroads of multiple TAAs' effects on GBM development, including promoting proliferation and invasion but also modulating immune response to tumor progression (Chen, Xia, et al, ; Jiang et al, ; Lee et al, ; Seike et al, ; Yin et al, ; Zamanian et al, ). This key cytokine might thus be considered as a target for new therapies but also as a specific biomarker since its expression has been observed as mostly associated with mesenchymal GBM (Jiang et al, ).…”

Standardization of sampling and sample preparation for analysis of human monocyte subsets in peripheral blood

“…CD16 + monocytes are suggested to be more efficient T-cell-activating cells than classical CD16monocytes [103]. [188]. High cell surface expression of CLIP can be viewed as an indicator of less effective antigen presentation [188,228], and these results imply this subset presents other peptide/MHCII complexes efficiently [188].…”