Strong Association of Combined Genetic Deficiencies in the Classical Complement Pathway With Risk of Systemic Lupus Erythematosus and Primary Sjögren's Syndrome

OBJECTIVE

Complete genetic deficiency of the complement component C2 is a strong risk factor for monogenic systemic lupus erythematosus (SLE), but whether heterozygous C2 deficiency adds to the risk of SLE or primary Sjögren's syndrome (SS) has not been studied systematically. This study was undertaken to investigate potential associations of heterozygous C2 deficiency and C4 copy number variation with clinical manifestations in patients with SLE and patients with primary SS.

METHODS

The presence of the common 28-bp C2 deletion rs9332736 and C4 copy number variation was examined in Scandinavian patients who had received a diagnosis of SLE (n = 958) or primary SS (n = 911) and in 2,262 healthy controls through the use of DNA sequencing. The concentration of complement proteins in plasma and classical complement function were analyzed in a subgroup of SLE patients.

RESULTS

Heterozygous C2 deficiency-when present in combination with a low C4A copy number-substantially increased the risk of SLE (odds ratio [OR] 10.2 [95% confidence interval (95% CI) 3.5-37.0]) and the risk of primary SS (OR 13.0 [95% CI 4.5-48.4]) when compared to individuals with 2 C4A copies and normal C2. For patients heterozygous for rs9332736 with 1 C4A copy, the median age at diagnosis was 7 years earlier in patients with SLE and 12 years earlier in patients with primary SS when compared to patients with normal C2. Reduced C2 levels in plasma (P = 2 × 10^-9 ) and impaired function of the classical complement pathway (P = 0.03) were detected in SLE patients with heterozygous C2 deficiency. Finally, in a primary SS patient homozygous for C2 deficiency, we observed low levels of anti-Scl-70, which suggests a risk of developing systemic sclerosis or potential overlap between primary SS and other systemic autoimmune diseases.

CONCLUSION

We demonstrate that a genetic pattern involving partial deficiencies of C2 and C4A in the classical complement pathway is a strong risk factor for SLE and for primary SS. Our results emphasize the central role of the complement system in the pathogenesis of both SLE and primary SS.

Adenoids provide a microenvironment for the generation of CD4(+), CD45RO(+), L-selectin(-), CXCR4(+), CCR5(+) T lymphocytes, a lymphocyte phenotype found in the middle ear effusion

Adenoidectomy in children with otitis media with effusion reduces inflammation in the middle ear by an unknown mechanism. Potentially, the adenoids of these children may serve as a site for the differentiation of lymphocytes, which after entering blood circulation eventually extravasate in the middle ear mucosa and thereby contribute to excessive inflammation. During lymphocyte extravasation various adhesion molecules and chemokines play a crucial role. To evaluate possible connections between the adenoids and middle ear inflammation, the expression of the chemokine receptors CXCR4 and CCR5 and the lymphocyte homing receptor L-selectin were analyzed in adenoidal and middle ear lymphocytes. It was found that most CD4(+) T lymphocytes in the middle ear effusion express the memory phenotype marker CD45RO and the chemokine receptors CXCR4 and CCR5, but are negative for the lymphocyte homing receptor L-selectin. This cell phenotype was rare in peripheral blood but was found much more frequently in the adenoids. The results suggest that the adenoids provide a microenvironment for the generation for CD4(+), CD45RO(+), L-selectin(-), CXCR4(+) and CCR5(+) T lymphocytes. Further, these cells may include cells that have the capacity to home to the middle ear mucosa. As the adenoidal CD4(+) memory phenotype CD45RO(+) T cells expressed the activation antigen CD69 and included cells expressing the HIV co-receptors CXCR4 and CCR5 at a high level, they may be permissive for HIV infection.

Metabolism of toremifene in the rat

Toremifene was labelled to a specific activity of about 20 microCi/mmol with tritium at positions 3 and 5 in the para-substituted phenyl ring. At these positions tritium is not eliminated within the metabolic pathways. A mixture of unlabelled and labelled toremifene (5 or 10 mg/kg, 5 microCi/mg) was given i.v. or p.o. to Sprague-Dawley rats. The elimination of radioactivity was followed up by collecting urine and feces daily for 13 days. The elimination of toremifene which was similar after p.o. and i.v. administration took place mainly in the feces. About 70% of the total radioactivity was eliminated within 13 days, of this amount more than 90% in the feces. All applied radioactivity could be detected in three separate fractions according to the oxidative state of the side chain when counted by Berthold TLC Linear Analyzer. Each fraction was further separated into single metabolites by TLC or HPLC. Altogether 9 metabolites were identified and almost all methanol-extractable components were identified. The main metabolic pathways in the rat were 4-hydroxylation and N-demethylation. The side chain was further oxidized to alcohols and carboxylic acids. Small amounts of unchanged toremifene were found in the feces both after p.o. and i.v. administration indicating biliary secretion.

Biotransformation of medetomidine in the rat

1. The metabolites of a novel alpha 2-adrenoceptor agonist, medetomidine, in rat urine after subcutaneous administration at two dose levels (80 micrograms/kg or 5 mg/kg), and after incubation with rat liver fractions, were characterized by h.p.l.c., 1H-n.m.r and mass spectrometry. 2. Hydroxylation of a methyl substituent was the main biotransformation in vitro. Hydroxylation occurred at a rate sufficient for high metabolic clearance. 3. The major urinary metabolites were the glucuronide of hydroxymedetomidine (about 35% of urinary metabolites) and medetomidine carboxylic acid (about 40%). 4. Medetomidine unchanged represented about 1% or 10% of the urinary excretion products, dependent on dose. 5. A metabolic pathway consisting of hydroxylation with subsequent glucuronidation, or further oxidation to carboxylic acid, is suggested.

Metabolism of detomidine in the rat. II. Characterisation of metabolites in urine

In order to investigate the biotransformation of a new alpha 2-adrenoceptor agonist, detomidine, metabolites were isolated from rat urine by solid phase extraction and purified by TLC. The isolated compounds were structurally analysed by 1H-NMR, MS and GC-MS as such or as their methyl and/or silyl derivatives. In addition to detomidine, which was found in trace amounts, four major metabolites were identified: hydroxymethyldetomidine, the corresponding O-glucuronide, detomidine carboxylic acid, and detomidine mercapturate. Together the identified components make up about 80% of urinary detomidine derived compounds. On the basis of these findings a major biotransformation pathway could be suggested. The reaction sequence is initiated by a hydroxylation. Subsequent glucuronidation, glutathione conjugation or secondary oxidation divide the route into three branches each producing one of the other three identified metabolites.