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Central European Journal of Immunology
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vol. 46
Clinical immunology

Increase in CD5L expression in the synovial membrane of knee osteoarthritis patients with obesity

Shintaro Shoji
Kentaro Uchida
1, 2
Gen Inoue
Ken Takata
Manabu Mukai
Jun Aikawa
Dai Iwase
Shotaro Takano
Hiroyuki Sekiguchi
Masashi Takaso

Department of Orthopedic Surgery, Kitasato University School of Medicine, Sagamihara City, Kanagawa, Japan
Shonan University of Medical Sciences Research Institute, Chigasaki City, Kanagawa, Japan
Cent Eur J Immunol 2021; 46 (2): 231-235
Online publish date: 2021/08/07
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Epidemiological studies suggest that obesity is a risk factor for osteoarthritis (OA), particularly knee osteoarthritis (KOA) [1-6]. Obesity results in high mechanical joint loading and elevated risk of KOA [3, 7]. Interestingly, studies have also suggested that altered metabolic conditions associated with obesity increase the production of growth factors and cytokines that are associated with KOA pathology [8, 9]. Moreover, the presence of OA in the hand joints of obese subjects [10, 11] suggests that mechanical factors are not the only type of factor in KOA progression. To date, however, the mechanisms of this effect have not been well established.
Synovial cells mainly consist of two populations, macrophages (M) and fibroblasts [12-14]. In particular, M contribute to synovial inflammation via inflammatory cytokine production in the synovial membrane (SM) [15-17]. CD5L has been identified as a M-secreted protein [18] and plays a role in modulation of the recruitment of M and inflammation [19]. CD5L is detected in both mouse and human serum [20-23] and is increased in the serum of obese mice [23]. CD5L protein in the synovial fluid (SF) of KOA patients was 3.3-fold higher than that in rheumatoid arthritis patients [24]. However, it is unclear whether cells in the SM express CD5L or whether CD5L expression is increased in the SM of KOA patients with obesity. Here, we investigated CD5L expression in the SM of obese KOA patients.

Material and methods


Ninety subjects who underwent primary total knee replacement (TKR) at our hospital participated in this study. SM was extracted during TKR from subjects with radiographically defined KOA. The protocol was approved by the Ethics Review Board of Kitasato University (approval number: B13-113), and participants provided written informed consent to participate in this study. The patient demographic profile is summarized in Table 1. All subjects were allocated to three groups based on body mass index (BMI): normal weight (NW, < 25 kg/m2), overweight (OW, 25-29.99 kg/m2) and obese (OB, ≥ 30 kg/m2), according to the World Health Organization (WHO) BMI classification.

CD5L expression in synovial membrane

RNA extraction, cDNA synthesis and quantitative RT-PCR (qRT-PCR) were conducted using previously reported methods [17]. CD5L primer pair sequences (product length: 152 bp) used in qRT-PCR analysis were: CD5L-Sense (5-CTT GCC ATT TGC ACC AGA CC-3) and CD5L-antisense (5-GCC ACG TCC TTA ATG TCC CA-3). CD14 and GAPDH primers were synthesized based on previous studies [17]. mRNA expression levels of CD5L in the SM were determined by normalization to that of GAPDH using the ∆∆CT method. We compared the expression of CD5L in the SM among the three groups. To evaluate the effect of aging on CD5L expression, patients were also grouped into two age groups, < 65 and ≥ 65 years, and CD5L expression in the two groups was compared.

CD5L-expressiong cells in synovial membrane

To evaluate CD5L-expressing cells, the CD14-positive (M) rich fraction was isolated from 3 SM samples. Following collagenase digestion, SM-derived cells were reacted with biotinylated anti-CD14 antibody, washed twice with PBS, streptavidin-labelled with magnetic particles (BD Biosciences, Tokyo, Japan), and reacted for 45 minutes at 4°C in a magnetic separation device (IMag, BD Biosciences). RPMI medium was added to the cell suspension to collect CD14– fractions, and an additional 3 ml of RPMI was added to collect the CD14+ fraction by removing the tube from the magnetic field. The CD14+ and CD14– fractions were obtained by centrifugation at 270 × γ for 5 minutes, and used to evaluate CD14 and CD5L expression using qRT-PCR. To confirm the CD5L expression, qRT-PCR products were subjected to electrophoresis and stained with ethidium bromide.


All statistical analyses were done using SPSS 25.0. Categorical variables were analyzed using the 2 test (two groups) and Fisher’s exact test (three groups). Continuous variables were compared using the t-test (two groups) and Bonferroni post hoc test (three groups). Statistical significance was defined by p < 0.05.


Patient demographic profiles in NW, OW, and OB groups

Following patient allocation to the three WHO BMI classification groups, those in the OB group were significantly younger than those in the NW group (p = 0.016, Table 1). Kellgren/Lawrence (K/L) grade 2/3/4 ratio and male/female ratio and were both similar among the groups (Table 1). CD5L expression in SM of NW, OW, and OB groups To determine whether CD5L expression is elevated in obese KOA patients, we analyzed expression levels in the SM of KOA patients. CD5L expression was significantly higher in the OB group than in the NW and OW groups (p < 0.001 and p < 0.001, respectively), but comparable between the NW and OW groups (p = 0.999) (Fig. 1).

Patient demographic profiles in the < 65 and ≥ 65 years groups

Kellgren/Lawrence (K/L) grade 2/3/4 ratio and male/female ratio and were both similar between the groups (Table 2).

CD5L expression in SM of < 65 and ≥ 65 years groups

Age significantly differed between the OB and other groups. To investigate the effect of aging, we compared CD5L expression between the < 65 and ≥ 65 years groups. There was no difference between the two groups (p = 0.629) (Fig. 2).

Expression of CD5L in synovial M

qRT-PCR analysis also revealed that CD14 mRNA levels in CD14+ fractions from the SM of KOA patients were higher than in CD14– fractions (p = 0.037, Fig. 3A). CD5L expression was observed in CD14+ cells in all patients. However, there was no detection in CD14– fractions in any patients (Fig. 3B).


Epidemic research has suggested a link between obesity and KOA progression [1, 25, 26]. KOA patients with obesity are approximately 7 times more likely to experience KOA progression than those of normal weight [1]. A meta-analysis revealed that the odds ratio for obese subjects with KOA development was 2.6 times that of normal weight subjects [25]. In the present study, KOA patients with obesity who underwent total knee arthroplasty (TKA) were significantly younger than OW and NW subjects. Together with previous reports, our observations suggest that obesity is associated with the pathology of KOA.
Inflammation plays a role in the progression and pain of KOA. Among findings to date, obesity was associated with synovial inflammation in human and animal studies [27, 28]; a high-fat diet led to synovial inflammation and promoted OA in rats [28]; and interleukin 6 (IL-6) levels were higher in the SF of obese hip OA patients than in hip OA patients of normal weight [27]. Regarding CD5L, levels were elevated in the course of metabolic and cardiovascular pathologies, such as in adipose tissue in obese mice [19] and in regions of atherosclerosis in mice [29]. CD5L contributes to M infiltration and inflammation in mice [19]. In the present study, CD5L expression in KOA patients with obesity was significantly higher than in normal and overweight patients. Obese groups contained a younger population than the normal weight group; however, CD5L expression did not differ between them. We speculate that CD5L contributes to synovial inflammation in OA patients with obesity, and that the elevation of CD5L in SM may partly explain the relationship between KOA pathology and obesity.
Synovial M contributes to synovial inflammation via the production of inflammatory cytokines and thereby contributes to OA pathology [15, 16, 30]. CD5L supports the survival of infiltrating macrophages, and overexpression of CD5L in CD5L transgenic mice remarkably increased the number of M in tissues [31]. CD5L deficiency also results in a reduction in macrophage infiltration in adipose tissue in obese mice [19]. In the present study, CD5L was specifically expressed in synovial M. CD5L may play an important role in synovial inflammation through the M in KOA.
In this study, we found that CD5L expression was elevated in SM of KOA patients with obesity. Further investigation of the precise role of CD5L in the relationship between KOA pathology and obesity is required. The authors declare no conflict of interest.


1. Coggon D, Reading I, Croft P, et al. (2001): Knee osteoarthritis and obesity. Int J Obes Relat Metab Disord 25: 622-627.
2. Felson DT (2005): Relation of obesity and of vocational and avocational risk factors to osteoarthritis. J Rheumatol 32: 1133-1135.
3. Felson DT (1996): Does excess weight cause osteoarthritis and, if so, why? Ann Rheum Dis 55: 668-670.
4. Hart DJ, Spector TD (1993): The relationship of obesity, fat distribution and osteoarthritis in women in the general population: the Chingford study. J Rheumatol 20: 331-335.
5. Lachance L, Sowers M, Jamadar D, et al. (2001): The experience of pain and emergent osteoarthritis of the knee. Osteoarthritis Cartilage 9: 527-532.
6. Runhaar J, Koes BW, Clockaerts S, Bierma-Zeinstra SM (2011): A systematic review on changed biomechanics of lower extremities in obese individuals: a possible role in development of osteoarthritis. Obes Rev 12: 1071-1082.
7. Powell A, Teichtahl AJ, Wluka AE, Cicuttini FM (2005): Obesity: a preventable risk factor for large joint osteoarthritis which may act through biomechanical factors. Br J Sports Med 39: 4-5.
8. Aspden RM (2011): Obesity punches above its weight in osteoarthritis. Nat Rev Rheumatol 7: 65-68.
9. Griffin TM, Guilak F (2008): Why is obesity associated with osteoarthritis? Insights from mouse models of obesity. Biorheology 45: 387-398.
10. Grotle M, Hagen KB, Natvig B, et al. (2008): Obesity and osteoarthritis in knee, hip and/or hand: an epidemiological study in the general population with 10 years follow-up. BMC Musculoskelet Disord 9: 132.
11. Oliveria SA, Felson DT, Cirillo PA, et al. (1999): Body weight, body mass index, and incident symptomatic osteoarthritis of the hand, hip, and knee. Epidemiology 10: 161-166.
12. Barland P, Novikoff AB, Hamerman D (1962): Electron microscopy of the human synovial membrane. J Cell Biol 14: 207-220.
13. Graabaek PM (1984): Characteristics of the two types of synoviocytes in rat synovial membrane. An ultrastructural study. Lab Invest 50: 690-702.
14. Mucke J, Hoyer A, Brinks R, et al. (2016): Inhomogeneity of immune cell composition in the synovial sublining: linear mixed modelling indicates differences in distribution and spatial decline of CD68+ macrophages in osteoarthritis and rheumatoid arthritis. Arthritis Res Ther 18: 170.
15. Takano S, Uchida K, Miyagi M, et al. (2016): Synovial macrophage-derived IL-1beta regulates the calcitonin receptor in osteoarthritic mice. Clin Exp Immunol 183: 143-149.
16. Takano S, Uchida K, Miyagi M, et al. (2016): Nerve growth factor regulation by TNF-αlpha and IL-1beta in synovial macrophages and fibroblasts in osteoarthritic mice. J Immunol Res 2016: 5706359.
17. Takano S, Uchida K, Inoue G, et al. (2017): Nerve growth factor regulation and production by macrophages in osteoarthritic synovium. Clin Exp Immunol 190: 235-243.
18. Gebe JA, Kiener PA, Ring HZ, et al. (1997): Molecular cloning, mapping to human chromosome 1 q21-q23, and cell binding characteristics of Spalpha, a new member of the scavenger receptor cysteine-rich (SRCR) family of proteins. J Biol Chem 272: 6151-6158.
19. Kurokawa J, Nagano H, Ohara O, et al. (2011): Apoptosis inhibitor of macrophage (AIM) is required for obesity-associated recruitment of inflammatory macrophages into adipose tissue. Proc Natl Acad Sci U S A 108: 12072-12077.
20. Gangadharan B, Antrobus R, Dwek RA, Zitzmann N (2007): Novel serum biomarker candidates for liver fibrosis in hepatitis C patients. Clin Chem 53: 1792-1799.
21. Gray J, Chattopadhyay D, Beale GS, et al. (2009): A proteomic strategy to identify novel serum biomarkers for liver cirrhosis and hepatocellular cancer in individuals with fatty liver disease. BMC Cancer 9: 271.
22. Kim HN, Kim YK, Lee IK, et al. (2009): Association between polymorphisms of folate-metabolizing enzymes and hematological malignancies. Leuk Res 33: 82-87.
23. Kurokawa J, Arai S, Nakashima K, et al. (2010): Macrophage-derived AIM is endocytosed into adipocytes and decreases lipid droplets via inhibition of fatty acid synthase activity. Cell Metab 11: 479-492.
24. Balakrishnan L, Bhattacharjee M, Ahmad S, et al. (2014): Differential proteomic analysis of synovial fluid from rheumatoid arthritis and osteoarthritis patients. Clin Proteomics 11: 1.
25. Blagojevic M, Jinks C, Jeffery A, Jordan KP (2010): Risk factors for onset of osteoarthritis of the knee in older adults: a systematic review and meta-analysis. Osteoarthritis Cartilage 18: 24-33.
26. Fletcher E, Lewis-Fanning E (1945): Chronic rheumatic diseases – Part IV: a statistical study of 1,000 cases of chronic rheumatism. Postgrad Med J 21: 176-185.
27. Pearson MJ, Herndler-Brandstetter D, Tariq MA, et al. (2017): IL-6 secretion in osteoarthritis patients is mediated by chondrocyte-synovial fibroblast cross-talk and is enhanced by obesity. Sci Rep 7: 3451.
28. Sun AR, Panchal SK, Friis T, et al. (2017): Obesity-associated metabolic syndrome spontaneously induces infiltration of pro-inflammatory macrophage in synovium and promotes osteoarthritis. PLoS One 12: e0183693.
29. Arai S, Shelton JM, Chen M, et al. (2005): A role for the apoptosis inhibitory factor AIM/Spalpha/Api6 in atherosclerosis development. Cell Metab 1: 201-213.
30. Uchida K, Satoh M, Inoue G, et al. (2015): CD11c(+) macrophages and levels of TNF-αlpha and MMP-3 are increased in synovial and adipose tissues of osteoarthritic mice with hyperlipidaemia. Clin Exp Immunol 180: 551-559.
31. Haruta I, Kato Y, Hashimoto E, et al. (2001): Association of AIM, a novel apoptosis inhibitory factor, with hepatitis via supporting macrophage survival and enhancing phagocytotic function of macrophages. J Biol Chem 276: 22910-22914.
Copyright: © 2021 Polish Society of Experimental and Clinical Immunology This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) License (http://creativecommons.org/licenses/by-nc-sa/4.0/), allowing third parties to copy and redistribute the material in any medium or format and to remix, transform, and build upon the material, provided the original work is properly cited and states its license.
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