CHARACTERIZATION OF COMPLEMENT C6 DEFICIENCY IN A PVG C RAT STRAIN/

Complement C6 plays an important role in the effector phase of complem ent-mediated cell lysis. Recently, a PVG/c rat strain deficient in hae molytic C6 activity was discovered. In the present study we show that these rats lack both antigenic and functional C6, and that repetitive immunization of these rats with PVG/c(+) serum results in generation o f specific anti-rat C6 antibodies. The observed absence of rat C6 was further investigated at the genomic and transcriptional level using a 492-bp cDNA of rat C6, cloned from a rat liver cDNA library using full length human C6 as a probe. Northern blot analysis revealed the prese nce of C6 mRNA in livers of both PVG/c(-) and PVG/c(+) rats, correspon ding to a size of approximate to 3.3 kb, although the level of C6 mRNA expression was approximate to 100-fold less in PVG/c(-) rats. In addi tion, using rat CB-specific primers, positive signals were obtained in kidneys of both rat strains by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Southern blot analysis of digested genomi c DNA did not reveal evidence for large C6 gene deletions. We conclude that the lack of C6 protein in the PVG/c(-) rat strain is not due to a (large) C6 gene deletion, but presumably is caused by an unstable mR NA or a point mutation in the C6 gene resulting in an aberrant transcr iption of the C6 gene. Alternatively, a gene coding for a product invo lved in C6 biosynthesis that acts in trans may carry a mutation.