SIGLEC1 and SIGLEC7 expression in circulating monocytes of patients with multiple sclerosis

Abstract

Background: Sialic acid binding immunoglobulin-like lectins (Siglecs) are cell surface receptors that recognize sialic acids and may attenuate immune responses and reduce inflammation. Objective: The purpose of this study was to investigate the role of two members of the Siglec family, SIGLEC1 and SIGLEC7, in the clinical course and disease activity of patients with multiple sclerosis (MS). Methods: SIGLEC1 and SIGLEC7 expression was determined by flow cytometry in the blood monocytes of 16 healthy controls and 55 untreated MS patients (13 primary progressive MS (PPMS) patients, 13 secondary progressive MS (SPMS) patients and 29 relapsing–remitting MS (RRMS) patients (18 during clinical remission and 11 during relapse)). Results: SIGLEC1 expression by CD14+ monocytes was significantly increased in MS patients compared with controls (p=0.025 for percentage of positive cells; p=0.007 for mean fluorescence intensity (MFI)). Stratification of patients into different clinical forms revealed increased SIGLEC1 expression in patients with progressive forms of the disease, particularly in those with PPMS (p=0.003 for percentage of positive cells and p=0.001 for MFI when compared with controls; p=0.031 for percentage of positive cells when compared with RRMS patients). Both inflammatory and resident monocytes contributed to the increase in SIGLEC1 expression observed in PPMS patients. SIGLEC7 expression was significantly up-regulated in blood monocytes from RRMS during relapse compared with patients during clinical remission (p=0.001 for MFI). Conclusions: These findings suggest roles for SIGLEC1 in the chronic progressive phases of MS and for SIGLEC7 in acute disease activity.