Genetic Variation Is the Major Determinant of Individual Differences in Leukocyte Endothelial Adhesion Michael A. Grassi 1 *, Vidhya Rao 1 , Kathryn P. Winkler 1 , Wei Zhang 2 , Joseph D. Bogaard 1 , Siquan Chen 3 , Bonnie LaCroix 6 , Divya Lenkala 6 , Jalees Rehman 4 , Asrar B. Malik 4 , Nancy J. Cox 5 , R. Stephanie Huang 6 1 Department of Ophthalmology & Visual Sciences, University of Illinois at Chicago, Chicago, Illinois, United States of America, 2 Department of Pediatrics, University of Illinois at Chicago, Chicago, Illinois, United States of America, 3 Cellular Screening Center, Institute for Genomics and Systems Biology, University of Chicago, Chicago, Illinois, United States of America, 4 Department of Pharmacology, University of Illinois at Chicago, Chicago, Illinois, United States of America, 5 Section of Genetic Medicine, University of Chicago, Chicago, Illinois, United States of America, 6 Section of Hematology/Oncology, University of Chicago, Chicago, Illinois, United States of America Abstract Objective: To determine the genetic contribution to leukocyte endothelial adhesion. Methods: Leukocyte endothelial adhesion was assessed through a novel cell-based assay using human lymphoblastoid cell lines. A high-throughput screening method was developed to evaluate the inter-individual variability in leukocyte endothelial adhesion using lymphoblastoid cell lines derived from different donors. To assess heritability, ninety-two lymphoblastoid cell lines derived from twenty-three monozygotic twin pairs and twenty-three sibling pairs were compared. These lymphoblastoid cell lines were plated with the endothelial cell line EA.hy926 and labeled with Calcein AM dye. Fluorescence was assessed to determine endothelial cell adhesion to each lymphoblastoid cell line. Intra-pair similarity was determined for monozygotic twins and siblings using Pearson pairwise correlation coefficients. Results: A leukocyte endothelial adhesion assay for lymphoblastoid cell lines was developed and optimized (CV = 8.68, Z9- factor = 0.67, SNR = 18.41). A higher adhesion correlation was found between the twins than that between the siblings. Intra- pair similarity for leukocyte endothelial adhesion in monozygotic twins was 0.60 compared to 0.25 in the siblings. The extent to which these differences are attributable to underlying genetic factors was quantified and the heritability of leukocyte endothelial adhesion was calculated to be 69.66% (p-value,0.0001). Conclusions: There is a heritable component to leukocyte endothelial adhesion. Underlying genetic predisposition plays a significant role in inter-individual variability of leukocyte endothelial adhesion. Citation: Grassi MA, Rao V, Winkler KP, Zhang W, Bogaard JD, et al. (2014) Genetic Variation Is the Major Determinant of Individual Differences in Leukocyte Endothelial Adhesion. PLoS ONE 9(2): e87883. doi:10.1371/journal.pone.0087883 Editor: Gerard Pasterkamp, University Medical Center Utrecht, Netherlands Received August 14, 2013; Accepted January 6, 2014; Published February 10, 2014 Copyright: ß 2014 Grassi et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: We gratefully acknowledge support from the following organizations for this research: NIH K08 EY019089-02, National Eye Institute Core Grant EY001792 for Vision Research and an unrestricted grant from Research to Prevent Blindness, Inc., New York, NY. RSH received support from NIH/NIGMS grant K08GM089941, NIH/NCI Grant R21 CA139278, NIH/NIGMS Pharmacogenomics of Anticancer Agents grant U01GM61393, the University of Chicago Breast Cancer SPORE Career Development Award, the University of Chicago Cancer Center Support Grant (#P30 CA14599) and the National Center for Advancing Translational Sciences of the NIH [UL1RR024999]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: grassim@uic.edu Introduction Leukocyte endothelial adhesion has been implicated as a key disease process in many conditions of major public health import such as multiple sclerosis, atherosclerosis, inflammatory bowel disease, diabetic retinopathy, malignancy, pulmonary edema, rheumatoid arthritis, and stroke [1,2]. Attempts to target leukocyte trafficking as a treatment for these conditions have been successful, but often have serious complications given the multiple off-target effects of many of these drugs e.g. prednisone [2,3]. Leukocyte– endothelial interactions are primarily attributed to cell-surface adhesion molecules including the integrins, members of the IgG superfamily, and selectins. There remain many other, yet undefined, molecules and signaling pathways that mediate leukocyte endothelial adhesion [4]. Improved characterization of the molecular underpinnings of leukocyte endothelial adhesion could have far reaching biomedical impact as it may improve therapeutic targeting and specificity for many common diseases. Genomic studies may have the capability of accomplishing this goal, but require there to be an underlying genetic basis for leukocyte endothelial adhesion. Corroborating lines of evidence suggest that genetic variability contributes to differences in leukocyte endothelial adhesion. For instance, it has been shown that the expression of cell surface adhesion molecules on endothelial cells varies between individuals [5] and is highly heritable. Rainwater et al. demonstrated that in the setting of TNF-a there is a significant genetic contribution to the expression of E-selectin, VCAM, and ICAM-1 [6]. Moreover, hematologic malignancies like leukemia caused by underlying chromosomal re-arrangements reveal differential gene expression PLOS ONE | www.plosone.org 1 February 2014 | Volume 9 | Issue 2 | e87883