Objectives To perform C1q, C2 and C4 molecular characterization in Juvenile Systemic Lupus Erythematosus (JSLE) patients.
Methods From JSLE cohort screened for complement deficiencies2 were selected P1 with undetectable C1q and normal C3 and C4; P2 with decreased C2 and C4; P3 with decreased C2, normal C3 and C4 and P4 with repeated decreased C4, normal C1q, C2 and C3. Primers were according to GenBank. Peripheral mononuclear cells from patients and 3 healthy controls were cultivated, stimulated with interferon gama, incubated for 36 h and quantitative RT-PCR verified gene mRNA expression.
Results C1q characterization (P1) revealed heterozygous silent mutations in A chain (c.276 A>G Gly) and C chain (c.126 C>T Pro). Two homozygous single-base exchanges were found in 5´UTR (c. -159 T>G) and 3’UTR (c*78 A>G) in B chain. Patient’s healthy mother had the same homozygous silent mutation in A chain, heterozygous silent mutation in C chain and single-base exchanges in B chain. She also had missense mutation in A chain (c.295 A>C Ile>Leu). Quantitative RT-PCR showed that (P1) C1qA gene mRNA expression without stimulation was 1.3 times decreased and with interferon gama was 1.6 times more expressed compare with healthy samples. C1qB gene expression without stimulation was 2.2 times decreased and stimulated was 1.5 times increased. Controls did not expressed C1qC and patient had low expression without and with stimulation. P2 and P3 had heterozygous C2 deficiency type I (28 bp deletion) and P2 also had 2 copies of C4A and 1 of C4B. The sequencing showed that exons, splicing sites, 5’UTR and 3’UTR matched 100% with reference sequence, exception to 28bp deletion. Patients’ mRNA expressions without stimulation was 23 times decreased and with interferon was 1.5 times increased. P4 had 2 copies of C4A and 3 of C4B and RT-PCR showed that C4B expression without stimulation was 14 times decreased and with interferon was 1.1 times increased. The C4A gene expression was not performed.
Conclusions We speculate whether single-base exchanges in 5’UTR in B chain, that correspond to promoter region, and in 3’UTR, that correspond to stabilization mRNA region, may have modified the transcription as it expression was decreased without stimulation. Further analyzes may relate C1q gene variations and undetectable C1q. In addition, heterozygous C2 deficiency type I leaded to reduced mRNA expression and may be present in JSLE patients with detectable C2 levels. Finally, C4B gene expression was decreased and shows that serum dosage and gene copy number may not be sufficient to asses C4 deficiency.
Carneiro-Sampaio M, et al. Understanding Systemic Lupus Erythematosus Physiopathology in the Light of Primary Immunodeficiencies. J Clin Immunol. 2008;28:S34-S41;
Jesus AA, et al. Complement and antibody primary immunodeficiency in juvenile systemic lupus erythematosus patients. Lupus 2011;20:1275-84;
Boeckler P, et al. Which complement assays and typings are necessary for the diagnosis of complement deficiency in patients with lupus erythematosus? A study of 25 patients. Clin Immunol. 2006;121:198-202. Financial support: FAPESP grant 2008/58238-4.
Disclosure of Interest None Declared