Drs. Szalai, Bullard, and Edberg contributed equally to this work.
Systemic Lupus Erythematosus
Multiple Lupus-Associated ITGAM Variants Alter Mac-1 Functions on Neutrophils
Article first published online: 28 OCT 2013
Copyright © 2013 by the American College of Rheumatology
Arthritis & Rheumatism
Volume 65, Issue 11, pages 2907–2916, November 2013
How to Cite
Zhou, Y., Wu, J., Kucik, D. F., White, N. B., Redden, D. T., Szalai, A. J., Bullard, D. C. and Edberg, J. C. (2013), Multiple Lupus-Associated ITGAM Variants Alter Mac-1 Functions on Neutrophils. Arthritis & Rheumatism, 65: 2907–2916. doi: 10.1002/art.38117
- Issue published online: 28 OCT 2013
- Article first published online: 28 OCT 2013
- Accepted manuscript online: 5 AUG 2013 03:17PM EST
- Manuscript Accepted: 30 JUL 2013
- Manuscript Received: 7 MAY 2013
- NIH. Grant Numbers: P01-AR-49084, 5P30-AR-048311, R21-AR-058864, R21-DA-026956
- National Center for Advancing Translational Sciences. Grant Number: UL1-TR-000165
- Lupus Research Institute
Multiple studies have demonstrated that single-nucleotide polymorphisms (SNPs) in the ITGAM locus (including the nonsynonymous SNPs rs1143679, rs1143678, and rs1143683) are associated with systemic lupus erythematosus (SLE). ITGAM encodes the protein CD11b, a subunit of the β2 integrin Mac-1. The purpose of this study was to determine the effects of ITGAM genetic variation on the biologic functions of neutrophil Mac-1.
Neutrophils from ITGAM-genotyped and -sequenced healthy donors were isolated for functional studies. The phagocytic capacity of neutrophil ITGAM variants was probed with complement-coated erythrocytes, serum-treated zymosan, heat-treated zymosan, and IgG-coated erythrocytes. The adhesion capacity of ITGAM variants, in adhering to either purified intercellular adhesion molecule 1 or tumor necrosis factor α–stimulated endothelial cells, was assessed in a flow chamber. Expression levels of total CD11b and activation of CD11b were assessed by flow cytometry.
Mac-1–mediated neutrophil phagocytosis, determined in cultures with 2 different complement-coated particles, was significantly reduced in individuals with nonsynonymous variant alleles of ITGAM. This reduction in phagocytosis was related to variation at either rs1143679 (in the β-propeller region) or rs1143678/rs1143683 (highly linked SNPs in the cytoplasmic/calf-1 regions). Phagocytosis mediated by Fcγ receptors was also significantly reduced in donors with variant ITGAM alleles. Similarly, firm adhesion of neutrophils was significantly reduced in individuals with variant ITGAM alleles. These functional alterations were not attributable to differences in total receptor expression or activation.
The nonsynonymous ITGAM variants rs1143679 and rs1143678/rs113683 contribute to altered Mac-1 function on neutrophils. These results underscore the need to consider multiple nonsynonymous SNPs when assessing the functional consequences of ITGAM variation on immune cell processes and the risk of SLE.