Abstract
The complement system plays a key role in several dermatological diseases. Overactivation, deficiency, or abnormality of the control proteins are often related to a skin disease. Autoimmune mechanisms with autoantibodies and a cytotoxic effect of the complement membrane attack complex on epidermal or vascular cells can cause direct tissue damage and inflammation, e.g., in systemic lupus erythematosus (SLE), phospholipid antibody syndrome, and bullous skin diseases like pemphigoid. By evading complement attack, some microbes like Borrelia spirochetes and staphylococci can persist in the skin and cause prolonged symptoms. In this review, we present the most important skin diseases connected to abnormalities in the function of the complement system. Drugs having an effect on the complement system are also briefly described. On one hand, drugs with free hydroxyl on amino groups (e.g., hydralazine, procainamide) could interact with C4A, C4B, or C3 and cause an SLE-like disease. On the other hand, progress in studies on complement has led to novel anti-complement drugs (recombinant C1-inhibitor and anti-C5 antibody, eculizumab) that could alleviate symptoms in diseases associated with excessive complement activation. The main theme of the manuscript is to show how relevant the complement system is as an immune effector system in contributing to tissue injury and inflammation in a broad range of skin disorders.
Highlights
The complement system refers to a group of up to 50 molecules that play a role in various clearance processes and in host defense against microorganisms
We have demonstrated that all borrelial subspecies causing human infections, including several strains of B. garinii, carry ospE genes to protect themselves against complement attack in vivo [78]
We have previously presented that outer surface protein E (OspE) interacts with the C-terminal short consensus repeats (SCRs) 19–20 of factor H (FH) [75, 83]
Summary
The complement system refers to a group of up to 50 molecules that play a role in various clearance processes and in host defense against microorganisms Most of these complement components are in blood plasma but some act on cell membranes as receptors for activated components or as regulators that protect host tissues. Human keratinocytes have been reported to produce the complement inhibitors factor H (FH) and factor H-like protein (FHL-1) as well as the C3b inactivator enzyme factor I for which FH and FHL-1 act as cofactors. The production of these factors is upregulated by interferon-γ (IFN-γ) [2, 3]. C3 [6], factor B [7], complement receptors CR1 and CR2 [8], cC1qR [9], and C5aR [10], and the www.frontiersin.org
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