Expression of the activating CD94/NKG2C killer lectin-like receptor (KLR) specific for HLA-E was analyzed in peripheral blood lymphocytes (PBLs) from healthy adult blood donors; the expression of other natural killer (NK) cell receptors (ie, CD94/NKG2A, KIR, CD85j, CD161, NKp46, NKp30, and NKG2D) was also studied. Human cytomegalovirus (HCMV) infection as well as the HLA-E and killer immunoglobulin-like receptor (KIR) genotypes were considered as potentially relevant variables associated with CD94/NKG2C expression. The proportion of NKG2C+ lymphocytes varied within a wide range (<0.1% to 22.1%), and a significant correlation (r = 0.83; P < .001) between NKG2C+ NK and T cells was noticed. The HLA-E genotype and the number of activating KIR genes of the donors were not significantly related to the percentage of NKG2C+ lymphocytes. By contrast, a positive serology for HCMV, but not for other herpesviruses (ie, Epstein-Barr and herpes simplex), turned out to be strongly associated (P < .001) with increased proportions of NKG2C+ NK and T cells. Remarkably, the CD94/NKG2C+ population expressed lower levels of natural cytotoxicity receptors (NCRs) (ie, NKp30, NKp46) and included higher proportions of KIR+ and CD85j+ cells than CD94/NKG2A+ cells. Altogether, these data support that HCMV infection selectively shapes the natural killer cell receptor (NKR) repertoire of NK and T cells from healthy carrier individuals.

CD94/NKG2C⁺ natural killer (NK) cells are increased in healthy individuals infected with human cytomegalovirus (HCMV), suggesting that HCMV infection may shape the NK cell receptor repertoire. To address this question, we analyzed the distribution of NK cell subsets in peripheral blood lymphocytes (PBLs) cocultured with HCMV-infected fibroblasts. A substantial increase of NK cells was detected by day 10 in samples from a group of HCMV⁺ donors, and CD94/NKG2C⁺ cells outnumbered the CD94/NKG2A⁺ subset. Fibroblast infection was required to induce the preferential expansion of CD94/NKG2C⁺ NK cells that was comparable with allogeneic or autologous fibroblasts, and different virus strains. A CD94-specific monoclonal antibody (mAb) abrogated the effect, supporting an involvement of the lectinlike receptor. Purified CD56⁺ populations stimulated with HCMV-infected cells did not proliferate, but the expansion of the CD94/NKG2C⁺ subset was detected in the presence of interleukin-15 (IL-15). Experiments with HCMV deletion mutants indicated that the response of CD94/NKG2C⁺ NK cells was independent of the UL16, UL18, and UL40 HCMV genes, but was impaired when cells were infected with a mutant lacking the US2-11 gene region. Taken together the data support that the interaction of CD94/NKG2C with HCMV-infected fibroblasts, concomitant to the inhibition of human leukocyte antigen (HLA) class I expression, promotes an outgrowth of CD94/NKG2C⁺ NK cells.

An increasing number of studies show how changes in intracellular metabolic pathways alter tumor and immune cell function. However, little information about metabolic changes in other cell types, including synovial fibroblasts, is available. In rheumatoid arthritis (RA), fibroblast-like synoviocytes (FLS) are the most common cell type at the pannus–cartilage junction and contribute to joint destruction through their production of cytokines, chemokines, and matrix-degrading molecules and by migrating and invading joint cartilage. In this review, we show that these cells differ from healthy synovial fibroblasts, not only in their marker expression, proto-oncogene expression, or their epigenetic changes, but also in their intracellular metabolism. These metabolic changes must occur due to the stressful microenvironment of inflamed tissues, where concentrations of crucial nutrients such as glucose, glutamine, and oxygen are spatially and temporally heterogeneous. In addition, these metabolic changes will increase metabolite exchange between fibroblast and other synovial cells, which can potentially be activated. Glucose and phospholipid metabolism as well as bioactive lipids, including sphingosine-1-phosphate and lysophosphatidic acid, among others, are involved in FLS activation. These metabolic changes likely contribute to FLS involvement in aspects of immune response initiation or abnormal immune responses and strongly contribute to joint destruction.

Objective: Up‐regulation of glucose metabolism has been implicated not only in tumor cell growth but also in immune cells upon activation. However, little is known about the metabolite profile in rheumatoid arthritis (RA), particularly in fibroblast‐like synoviocytes (FLS). This study was undertaken to evaluate whether changes in glucose metabolism in RA FLS could play a role in inflammation and joint damage.Methods: Synovium and FLS were obtained from patients with RA and patients with osteoarthritis (OA). The rate of glycolysis after stimulation of FLS with lipopolysaccharide and platelet‐derived growth factor BB was measured using glycolysis stress test technology. FLS function was evaluated using a glycolysis inhibitor, 2‐deoxy‐d‐glucose (2‐DG). After stimulation of the FLS, a migration scratch assay, MTT assay, and enzyme‐linked immunosorbent assay were performed to measure the effect of 2‐DG on FLS migration, viability of the FLS, and cytokine secretion, respectively. IRDye 800CW 2‐DG was used to assess glucose uptake in the arthritic joints and stromal cells of mice after K/BxN mouse serum transfer. The mice were injected daily, intraperitoneally, with 3‐bromopyruvate (BrPa; 5 mg/kg) to assess the effect of inhibition of glycolysis in vivo.Results: Compared to human OA FLS, the balance between glycolysis and oxidative phosphorylation was shifted toward glycolysis in RA FLS. Glucose transporter 1 (GLUT1) messenger RNA (mRNA) expression correlated with baseline functions of the RA FLS. Glucose deprivation or incubation of the FLS with glycolytic inhibitors impaired cytokine secretion and decreased the rate of proliferation and migration of the cells. In a mouse model of inflammatory arthritis, GLUT1 mRNA expression in the synovial lining cells was observed, and increased levels of glucose uptake and glycolytic gene expression were detected in the stromal compartment of the arthritic mouse joints. Inhibition of glycolysis by BrPa, administered in vivo, significantly decreased the severity of arthritis in this mouse model.Conclusion: Targeting metabolic pathways is a novel approach to understanding the mechanisms of disease. Inhibition of glycolysis may directly modulate synoviocyte‐mediated inflammatory functions and could be an effective treatment strategy for arthritis.