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Review
. 2021 Feb 10;23(3):16.
doi: 10.1007/s11926-021-00984-1.

A Review of Complement Activation in SLE

Arthur Weinstein  1   2   3 , Roberta V Alexander  4 , Debra J Zack  4
Affiliations
Review

A Review of Complement Activation in SLE

Arthur Weinstein et al. Curr Rheumatol Rep. .

Abstract

Purpose of review: Complement activation is a key event in the pathogenesis of tissue inflammation and injury in systemic lupus erythematosus (SLE). This review is aimed at comparing the usefulness of measurement of complement proteins in serum/plasma (C3, C4) to complement activation (split) products in plasma and on circulating blood cells for SLE diagnosis, disease monitoring, and prognosis.

Recent findings: Complement split products, C3dg, iC3b, and C4d, are elevated in SLE, and C3dg/C3 and iC3b/C3 ratios correlate with active SLE. C4d also is higher in patients with lupus nephritis. An elevated level of the alternative pathway split product, Bb, in early lupus pregnancy is a predictor of adverse outcomes in SLE patients with antiphospholipid antibodies. Elevated levels of cell-bound complement activation products (CB-CAPs), namely, B cell-bound C4d (BC4d) and erythrocyte-bound C4d (EC4d), within a multiparameter assay panel, may predict transition to SLE more than other lupus biomarkers. EC4d better correlates with lupus disease activity than low plasma complement levels. Elevated platelet-bound C4d (PC4d) correlates with thrombosis in SLE. Both EC4d and PC4d are increased in primary and secondary anti-phospholipid syndrome, and anti-beta2glycoproteinI antibodies may directly activate the complement system. Abnormal levels of plasma complement split products and CB-CAPs support complement activation as an important pathogenetic mechanism in SLE and the antiphospholipid syndromes. These tests show promise for the diagnosis of SLE and monitoring of disease activity.

Keywords: Complement; Complement activation measurement; Disease activity; Lupus nephritis; Systemic lupus erythematosus.

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Conflict of interest statement

AW is a research consultant to Exagen Inc. He has received > $10,000 stock options. RVA and DJA are employees of Exagen Inc.

Figures

Fig. 1
Fig. 1
Pathways of complement activation. Classical pathway activators include surface-bound IgG and IgM and circulating immune complexes. MBL mannose-binding lectin, MASP MBL-associated serine proteinases. Red arrows show feedback (amplification) loops. Modified from Morgan BP: Complement. In: Male D, Brostoff J, Roth DB, Roitt IM, editors. Immunology. 8th edition, Elsevier, 2012
See this image and copyright information in PMC

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