Caracterização imunológica e genética da deficiência do componente C5 do sistema complemento humano.

Abstract

AGUILAR-RAMIREZ, P. Immunological and genetic characterization of the deficiency of the component C5 of the human complement system. Master thesis (Immunology) Instituto de Ciencias Biomedicas, Universidade de Sao Paulo, 2007. The deficiency of the C5 component of the complement system is rare. Only 38 described cases were described in the literature. This deficiency is frequently associated with severe and recurrent infections, especially caused by Neisseria. The deficient patients sera have less bactericidal activity and reduced production of chemotactic factors. Moreover, their sera fail to properly activate the complement system. We found complete absence of C5 in the serum of 3 members (II:4, II:5 e II:9) of a family with history of consanguinity. Five members of this family had suffered from recurrent episodes of meningitis, and other less severe infections. Our general objective is to characterize immunologically and genetically this deficiency, the first of its type described in the Brazilian population. Using double immunodifusion and radial immunodifusion we noted that C3, C4, C6, C7, C8, C9, Factor B, Factor H and Factor I have expressive levels in all the individuals of this family, C5 was absent in individuals II:4, II:5 and II:9 serum. This siblings contained lowest concentrations of C5 (0.9; 1.0; 1.3 μg/ml normal concentration in health Brazilian: 45 – 190 μg/ml) when evaluated by ELISA. The probands sera II:4, II:5 e II:9 were also unable to mediate the hemolytic activity by the classical and alternative pathways. When purified C5 was added to the deficient serum at approximately physiological level, hemolytic activity was restored to close to normal levels. Furthermore, the father’s serum (I:2) presented only 25% of hemolytic activity mediated by the classical pathway and followed normal activity mediated by the alternative pathway. The I:2 sera presented normal levels of C1s and C4. Using RT-PCR of mRNA C5 obtained from the fibroblasts one of deficient (II:9), we detected a silent mutation of ACC to ACT, both codons are responsible for the codification of Thr. Individuals I:1, I:2, II:4 and II:9 have a deletion in the C5 cDNA located between nucleotides 3876 4029, correspondent to exon 30. Studies shown that this delecao is due to the substitution of GAG for a GAA in the last codon of exon 30 that leads to exon 30 skiping during the processing of the C5 RNAm. This defect was responsible for the deficiency of C5 in this family, probably in function of the production of an incomplete, unstable protein and more quickly degraded after its synthesis.