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Ann Rheum Dis. 2012 Dec;71(12):2028-34. doi: 10.1136/annrheumdis-2012-201390. Epub 2012 May 14.

The rs1143679 (R77H) lupus associated variant of ITGAM (CD11b) impairs complement receptor 3 mediated functions in human monocytes.

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1
Genetics and Molecular Medicine and Immunology, Infection and Inflammatory Disease, King’s College London, London, UK.

Abstract

OBJECTIVES:

The rs1143679 variant of ITGAM, encoding the R77H variant of CD11b (part of complement receptor 3; CR3), is among the strongest genetic susceptibility effects in human systemic lupus erythematosus (SLE). The authors aimed to demonstrate R77H function in ex-vivo human cells.

METHODS:

Monocytes/monocyte-derived macrophages from healthy volunteers homozygous for either wild type (WT) or 77H CD11b were studied. The genotype-specific expression of CD11b, and CD11b activation using conformation-specific antibodies were measured. Genotype-specific differences in iC3b-mediated phagocytosis, adhesion to a range of ligands and the secretion of cytokines following CR3 ligation were studied. The functionality of R77H was confirmed by replicating findings in COS7 cells expressing variant-specific CD11b.

RESULTS:

No genotype-specific difference in CD11b expression or in the expression of CD11b activation epitopes was observed. A 31% reduction was observed in the phagocytosis of iC3b opsonised sheep erythrocytes (sRBC(iC3b)) by 77H cells (p=0.003) and reduced adhesion to a range of ligands: notably a 24% reduction in adhesion to iC3b (p=0.014). In transfected COS7 cells, a 42% reduction was observed in phagocytosis by CD11b (77H)-expressing cells (p=0.004). A significant inhibition was seen in the release of Toll-like receptor 7/8-induced pro-inflammatory cytokines from WT monocytes when CR3 was pre-engaged using sRBC(iC3b), but no inhibition in 77H monocytes resulting in a significant difference between genotypes (interleukin (IL)-1β p=0.030; IL-6 p=0.029; tumour necrosis factor alpha p=0.027).

CONCLUSIONS:

The R77H variant impairs a broad range of CR3 effector functions in human monocytes. This study discusses how perturbation of this pathway may predispose to SLE.

PMID:
22586164
PMCID:
PMC3488763
DOI:
10.1136/annrheumdis-2012-201390
[Indexed for MEDLINE]
Free PMC Article
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