Chitin enhances obese inflammation ex vivo Chun-Jung Huang a,⇑ , Kathleen N. Beasley b , Edmund O. Acevedo c , Robert L. Franco c , Tamekia L. Jones d , David C. Mari a , Yoshimi Shibata e a Department of Exercise Science and Health Promotion, Florida Atlantic University, Boca Raton, FL, United States b School of Pharmacy, University of Southern California, Los Angeles, CA, United States c Department of Health and Human Performance, Virginia Commonwealth University, Richmond, VA, United States d Children’s Foundation Research Institute, Departments of Pediatrics and Preventive Medicine, University of Tennessee Health Science Center, Memphis, TN, United States e Department of Biomedical Science, College of Medicine, Florida Atlantic University, Boca Raton, FL, United States article info Article history: Received 16 April 2013 Accepted 11 September 2013 Available online 17 September 2013 abstract Infection has been implicated as a co-risk factor for obesity, but the mechanism remains uncertain. Elevated levels of plasma chitinase 3-like 1 (CHI3L1) are found in obese individuals. Since CHI3L1 is produced by acti- vated immune cells including macrophages and recognizes microbial N-acetylglucosamine polymer (chi- tin), we asked whether the plasma CHI3L1 protein change in obese individuals might alter their innate immune response to chitin. Thirty-six subjects (15 obese and 21 non-obese), ages 18–30 years, were recruited. Peripheral blood mononuclear cells (PBMCs) were cultured with chitin microparticles (CMP; 1–10 lm) for 24 h; tumor necrosis factor a (TNF-a), interleukin 6 (IL-6), and CHI3L1 in the culture super- natants were measured. We chose CMP, since neither large chitin beads (40–100 lm), chitosan micropar- ticles (1–10 lm), nor soluble chitin induced the cytokine/CHI3L1 production by PBMCs isolated from non-obese PBMCs ex vivo. We found that the quantity of IL-6, but not TNF-a or CHI3L1, induced by CMP was significantly correlated with plasma IL-6, BMI, waist/hip circumferences, fasting plasma insulin, and insulin resistance. These findings suggest that chitin, a substrate of CHI3L1, further promotes obese inflam- mation in a size- and chemical composition- dependent manner. Ó 2013 American Society for Histocompatibility and Immunogenetics. Published by Elsevier Inc. All rights reserved. 1. Introduction The epidemic of obesity and overweight continues to grow in the United States, with recent reports indicating over 64.1% of American women and 72.3% of American men are categorized as having a body mass index (BMI) P25 [1]. Such reports are partic- ularly alarming since obesity enhances the risk of numerous chronic inflammatory diseases, including diabetes, cardiovascular diseases (CVDs), and asthma [2,3]. These obesity-attributable ill- nesses have been discovered to have a strong association with inflammatory parameters in plasma. These parameters include: elevation of pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-a) and interleukin-6 (IL-6) [4,5], chitinase 3-like 1 protein (CHI3L1, a lectin binding chitin with no hydrolytic activ- ity) [6], and leptin (an adipocyte-derived hormone) [7]; and de- crease of intelectin-1 (ITLN-1, a lectin that recognizes bacterial galactofuranosyl carbohydrates) [8]. In addition to plasma inflam- matory mediators, the circulating mononuclear cells in obese indi- viduals may be more readily stimulated to produce inflammatory cytokines [9]. This occurrence seems to be pivotal to understanding additional agents including microbial products up-regulating the inflammatory conditions in obese individuals. Elevated plasma levels of CHI3L1 have been observed in obese individuals [6,10] as well as other inflammatory-related illnesses in humans, such as inflammatory bowel disease (IBD), colon can- cer, breast cancer, rheumatoid arthritis, bronchial asthma, type 2 diabetes, coronary artery disease, and Alzheimer’s disease [11– 16]. Local inflamed tissues such as intestinal mucosa in IBD [13] and adipose tissues in type 2 diabetes [14] produce CHI3L1 locally. Particularly immune cells including tissue macrophages (MØ) that are activated locally would be considered as major CHI3L1 produc- ers [13], although exact mechanisms regulating plasma CHI3L1 concentrations remain unclear. Several lines of evidence indicate that CHI3L1 enhances the recognition and interaction of chitin-containing pathogens by epithelial cells and MØ, leading to a pro-inflammatory response [13,17–18]. CHI3L1 stimulates production of inflammatory mediators (e.g., CCL2, CXCL2, MMP-9) [19], induces angiogenesis in cancer [20,21], and has been proposed as a pro-inflammatory biomarker [22–24]. Leptin is also known to play a key role in medi- ating pro-inflammatory state in obese individuals. Leptin not only induces pro-inflammatory cytokine productions [25,26] but also 0198-8859/$36.00 - see front matter Ó 2013 American Society for Histocompatibility and Immunogenetics. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.humimm.2013.09.005 ⇑ Corresponding author. Address: 777 Glades Road, FH11A-126B, Boca Raton, FL 33431, United States. Fax: +1 (561) 297 2839. E-mail address: chuang5@fau.edu (C.-J. Huang). Human Immunology 75 (2014) 41–46 Contents lists available at ScienceDirect www.ashi-hla.org journal homepage: www.elsevier.com/locate/humimm