Complement Receptor 1 (CR1, CD35) Polymorphisms and Soluble CR1: A Proposed Anti-inflammatory Role to Quench the Fire of "Fogo Selvagem" Pemphigus Foliaceus.

Pemphigus foliaceus is an autoimmune disease that is sporadic around the world but endemic in Brazil, where it is known as fogo selvagem (FS). Characterized by autoantibodies against the desmosomal cadherin desmoglein 1, FS causes painful erosions, and crusts that may be widespread. The recognition of antigens, including exposed sugar moieties, activates the complement system. Complement receptor 1 (CR1, CD35), which is responsible for the Knops blood group on erythrocytes (York and McCoy antigens), is also expressed by antigen-presenting cells. This regulates the complement system by removing opsonized antigens, blocking the final steps of the complement cascade. Membrane-bound CR1 also fosters antigen presentation to B cells, whereas soluble CR1 has anti-inflammatory properties. CR1 gene polymorphisms have been associated with susceptibility to complex diseases. In order to investigate the association of CR1 polymorphisms with FS susceptibility, we developed a multiplex sequence-specific assay to haplotype eleven polymorphisms in up to 367 FS patients and 242 controls from an endemic area and 289 from a non-endemic area. We also measured soluble CR1 (sCR1) in the serum of 53 FS patients and 27 controls and mRNA levels in the peripheral blood mononuclear cells of 63 genotyped controls. The haplotypes CR1*3B2B (with the York antigen-encoded by p.1408Met) and CR1*3A2A (with p.1208Arg) were associated with protection against FS (OR = 0.57, P = 0.027, and OR = 0.46, P = 0.014, respectively). In contrast, the CR1*1 haplotype (with the McCoy antigen - encoded by p.1590Glu) was associated with FS susceptibility (OR = 4.97, P < 0.001). Heterozygote rs12034383*A/G individuals presented higher mRNA expression than homozygotes with the G allele (P = 0.04). The lowest sCR1 levels occurred in patients with active disease before treatment (P = 0.036). Patients in remission had higher levels of sCR1 than did healthy controls (P = 0.013). Among those under treatment, patients with localized lesions also presented higher sCR1 levels than those with generalized lesions (P = 0.0073). In conclusion, the Knops blood group seems to modulate susceptibility to the disease. Furthermore, corticosteroid treatment might increase sCR1 serum levels, and higher levels may play an anti-inflammatory role in patients with FS, limiting the distribution of lesions. Based on these results, we suggest CR1 as a potential new therapeutic target for the treatment of FS.

Differential gene expression levels might explain association of LAIR2 polymorphisms with pemphigus.

The leukocyte-associated immunoglobulin-like receptor 1 (LAIR-1) is a collagen-binding inhibitory receptor important for the regulation of immune responses, expressed on the majority of peripheral blood mononuclear cells (PBMC). LAIR-2 is a soluble homolog that antagonizes LAIR-1 inhibitory function by binding the same ligands. We sought to investigate whether LAIR1 and LAIR2 single nucleotide polymorphisms (SNP) are associated with differential mRNA expression levels. We analyzed 14 SNPs of LAIR1 (6) and LAIR2 (8) by mass spectrometry-based genotyping and extracted mRNA from PBMC of 177 healthy subjects, followed by quantitative assays. Four SNPs of LAIR1 and two SNPs of LAIR2 mark differential mRNA levels in healthy individuals. To verify the biological relevance of these findings, we analyzed additional 515 individuals (282 patients and 233 controls) to check if LAIR1 and LAIR2 differential mRNA expression could be related to susceptibility to pemphigus foliaceus (PF), an autoimmune blistering skin disease endemic in Brazil. Two LAIR1 variants (rs56802430 G, OR = 1.52, p = 0.0329; rs11084332 C, OR = 0.57, p = 0.0022) and one LAIR2 (rs2287828 T+, OR = 1.9, p = 0.0097) contribute to differential susceptibility to PF. Furthermore, we demonstrate interactions among four LAIR2 SNPs (rs2042287, rs2287828, rs2277974 and rs114834145). A haplotype harboring these SNPs is strongly associated with higher LAIR2 mRNA levels (4.5-fold, p = 0.0069) and with higher susceptibility to PF (OR = 4.02, p = 0.0008). We suggest that LAIR1 and LAIR2 genetic variants are associated with regulation of gene expression and variable PF susceptibility, and show indirect association of LAIR2 differential mRNA expression with PF pathogenesis. Our data demonstrate how this relatively unknown disease can add invaluable knowledge regarding the role of LAIR1 and LAIR2 in immune responses.