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Enrichment of HLA-DR+ neutrophils in osteoarthritic infrapatellar fat pad

ABSTRACT: Neutrophils are increasingly recognized as functionally versatile immune cells, with tissue-specific phenotypes that extend beyond their classical role in acute inflammation. In osteoarthritis (OA), neutrophils are abundant in synovial fluid (SF) which has been linked to worse symptoms., yet their presence and function within the infrapatellar fat pad (IFP) remain poorly defined. Here, we characterized neutrophils in OA IFP using flow cytometry, immunofluorescence, proteomics, and functional assays. Weand identified a distinct population of HLA-DR⁺ neutrophils enriched in OA IFP. compared to matched SF. These cells co-expressed classical neutrophil markers and antigen presentation markers. Sorted IFP HLA-DR+ neutrophils induced proliferation of autologous CD3⁺ T cells, supporting a role in antigen presentation. Proteomic profiling of OA IFP revealed upregulation of metabolic and enzymatic activities as well as downregulation of apoptotic and enzyme inhibition pathways, consistent with the increased fibrosis and neovascularization observed histologically. Our findings suggest that IFP-resident neutrophils adopt a tissue adapted, antigen-presenting phenotype, with potential roles in T cell activation, fibrosis, and angiogenesis. Collectively, our findings expand the functional scope of neutrophils in arthritic diseases, further establishing their potential in antigen presentation, and positions the IFP as a previously underappreciated, immunologically active niche in OA pathogenesis.

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ORGANISM(S): Homo Sapiens (human)

DISEASE(S): Osteoarthritis

SUBMITTER: Susana Bravo

LAB HEAD: Susana B Bravo

PROVIDER: PXD073289 | Pride | 2026-03-23

REPOSITORIES: Pride

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Project description:HLA-DR molecules are highly expressed in synovial tissue (ST), the target of the immune response in chronic inflammatory arthritides, including in rheumatoid arthritis (RA) and Lyme arthritis (LA). In the current study, we identified HLA-DR-presented self-peptides (T cell epitopes) in ST, synovial fluid mononuclear cells (SF), and peripheral blood mononuclear cells (PB) from five patients with RA and eight with LA. Altogether, from 22 samples, 1,532 non-redundant HLA-DR-presented peptides were identified that were derived from 778 source proteins. Moreover, as the study progressed, application of newer, high sensitivity LC-MS instruments resulted in the identification of larger numbers of HLA-DR-presented peptides. Surprisingly, the source proteins for HLA-DR-presented peptides were as likely to have intracellular as extracellular locations. Although the number of peptides identified was greater in ST than in SF or PB, 68% of the peptides identified in SF were found in ST, and 55% of the peptides in PB were found in ST. Two RA patients had the same HLA-DR genotype (DRB1*0401 and 0101), and 44% of the peptides identified in these two patients were the same. In contrast, among the patients with RA or LA who had no shared HLA-DR alleles, only 6% of the peptides were the same. In the RA patients, HLA-DR-presented peptides were identified from source proteins that are thought to serve as potential autoantigens: collagen, enolase, fibrinogen, fibronectin, immunoglobulin and vimentin. Interestingly, peptides from these same source proteins were also commonly found in LA patients. However, citrullinated T cell epitopes were not identified in any patient. Thus, LC-MS/MS techniques are now sensitive enough to identify large numbers of T cell epitopes from tissue or fluids in individual patients. Importantly, analysis of SF or PB allowed us to identify a broader range of HLA-DR-presented self-peptides from individual patients and from patients seen earlier in the disease.

			Action	DRS
	OA_1.wiff	Wiff
	OA_1.wiff.scan	Wiff
	OA_2.wiff	Wiff
	OA_2.wiff.scan	Wiff
	OA_3.wiff	Wiff

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Enrichment of HLA-DR+ neutrophils in osteoarthritic infrapatellar fat pad

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