Immune cell profiles in synovial fluid after anterior cruciate ligament and meniscus injuries

Abstract

Background Anterior cruciate ligament (ACL) and meniscus tears are common knee injuries. Despite the high rate of post-traumatic osteoarthritis (PTOA) following these injuries, the contributing factors remain unclear. In this study, we characterized the immune cell profiles of normal and injured joints at the time of ACL and meniscal surgeries. Methods Twenty-nine patients (14 meniscus-injured and 15 ACL-injured) undergoing ACL and/or meniscus surgery but with a normal contralateral knee were recruited. During surgery, synovial fluid was aspirated from both normal and injured knees. Synovial fluid cells were pelleted, washed, and stained with an antibody cocktail consisting of fluorescent antibodies for cell surface proteins. Analysis of immune cells in the synovial fluid was performed by polychromatic flow cytometry. A broad spectrum immune cell panel was used in the first 10 subjects. Based on these results, a T cell-specific panel was used in the subsequent 19 subjects. Results Using the broad spectrum immune cell panel, we detected significantly more total viable cells and CD3 T cells in the injured compared to the paired normal knees. In addition, there were significantly more injured knees with T cells above a 500-cell threshold. Within the injured knees, CD4 and CD8 T cells were able to be differentiated into subsets. The frequency of total CD4 T cells was significantly different among injury types, but no statistical differences were detected among CD4 and CD8 T cell subsets by injury type. Conclusions Our findings provide foundational data showing that ACL and meniscus injuries induce an immune cell-rich microenvironment that consists primarily of T cells with multiple T helper phenotypes. Future studies investigating the relationship between immune cells and joint degeneration may provide an enhanced understanding of the pathophysiology of PTOA following joint injury.

Construction and analysis of a lncRNA–miRNA–mRNA competing endogenous RNA network from inflamed and normal synovial tissues after anterior cruciate ligament and/or meniscus injuries

“…Similarly, studies have revealed that high percentages of Th cells are present in blood samples and synovial fluid from RA and OA subjects ( Lurati et al, 2015 ; Rosshirt et al, 2019 ). Recently, Kim-Wang et al (2021) also found that the numbers of immune cells, primarily T cells with multiple Th phenotypes, are elevated in the synovial fluid following ACL and meniscus injuries, while the numbers of Th1, Th2, and Th17 cells are the dominant populations of the CD4 subsets. Furthermore, T17 cells can produce IL-17, which causes synovial fibroblasts, chondrocytes, macrophages, and osteoclasts to elicit a cascade and finally promotes inflammation, cartilage degradation, and changes in bone metabolism ( Koenders et al, 2006 ).…”

“…Previous studies have revealed that subjects diagnosed with primary OA exhibit elevated percentages of activated macrophages and T cells in peripheral blood, synovial fluid, and synovial tissues ( Li et al, 2017 ; Rosshirt et al, 2019 ). Specifically, a recent study has revealed a T-cell-predominant immune profile in the synovial fluid following ACL and meniscus injuries ( Kim-Wang et al, 2021 ). The immune cells present after joint injuries may play a vital role in the development of PTOA.…”

“…Recently, proteomic analyses have been performed on synovial fluid collected from patients after acute ACL injury ( King et al, 2020 ). In addition, the immune cell profiles of the joint synovial fluid from individuals with ACL or meniscus injuries have been evaluated ( Kim-Wang et al, 2021 ). However, the synovial membrane profiles that contribute to or mediate OA progressive cartilage degradation and joint dysfunction have not been studied in patients with ACL and meniscus injuries ( Ayral et al, 2005 ; Sellam and Berenbaum, 2010 ; Robinson et al, 2016 ).…”

Anterior Cruciate Ligament Reconstruction Surgery: Creating a Permissive Healing Phenotype in Military Personnel and Civilians for Faster Recovery

“…Within minutes of injury, the local and systemic immune response is activated. 46 , 47 Resident macrophages, natural killer (NK) cells, and fibroblasts from the synovium; lymphocytes, mast cells, and dendritic cells from the perivascular tissues; and osteoclasts from bone marrow are released by local damage stimuli. 46–48 In the first few hours, these activated cells lead to the influx of blood-borne neutrophils, monocytes, T helper cells, and B cells that enter the joint capsule to facilitate wound healing to initiate cleanup, cell proliferation, and remodeling.…”

“… 52 , 53 Resident innate NK cells also secrete cytokines, such as interferon-γ (IFN-γ) and tumor necrosis factor-alpha (TNF-α), and interact with macrophages, and other immune cells, to enhance the response. 47 , 54 These different immune and non-immune cells, through their cytokine networks, play pivotal roles both as activator cells and target effector cells to produce the correct healing response. 46 Within the joint, the synovial membrane regulates the traffic by maintaining a rich network of sympathetic and sensory nerves, blood vessels, and lymphatic vasculature to promote healing.…”