Differential interaction of gC1qR protein with the capsid proteins of porcine circoviruses.

Porcine circovirus type 2 (PCV-2) is the causal agent of the post weaning multisystemic wasting syndrome (PWMS). This virus is different from PCV-1 that is non-pathogenic. Globally PCV-2 strains are classified in two genogroups: a and b. PCV genome contains two major ORF that encode Rep and Rep’ proteins associated to the viral replication and the capsid protein (Cap) that is the unique structural component of the virus. The Capsid protein of circovirus interacts with the cell protein gC1qR that is the membranar receptor of the globular head of the complement protein C1q. This study aimed to determine the expression level of gC1qR transcripts infected by PCV-2, to determine the region of PCV-2 Cap required for the interaction with gC1qR and to evaluate the interaction between gC1qR and different strains of PCV.

Infection of piglets and RT-PCR: 4 piglets were infected by intramuscular and intratracheal route by PCV-2.Three days after infection samples were collected from mesenteric, inguinal and tracheo-brochial lymph nodes and spleen on tonsils.The levels of gC1qR transcripts and the PCV-2 viral genomic loads were determined by real time PCR. Yeast two hybrid assay:

DNA sequences comprising the mature proteins of gC1qR has been amplified from PK-15 cells and a spleen cDNA library and then cloned into the pGADT7 plasmid.The Cap proteins of PCV-2a,PCV-2b and two strains of PCV-1 have been cloned in the pGBKT7 plasmid.The yeast Y2HGOLD from Clonetech was co-transformed by different combination of pGADT7 and pGBKT7 constructions and plated on double drop out medium SD-2 (-Leu,-Trp) and incubated for four days at 30°C. The yeast colonies obtained were used for making patches on SD-2 medium that were further incubated for two days at 30°C and duplicated on SD-2 plates and quadruple drop out medium SD-4 for determine protein interaction.

We have shown that the gC1qR transcripts are downregulated in the tracheobronchial lymph nodes of piglets infected by PCV-2, three days after infection. We have shown that the 59 N-terminal amino acids of PCV-2 Cap is required for the interaction with gC1qR. Furthermore gC1qR interacts with PCV-2a Cap, PCV-2b Cap but also with the Cap protein of a PCV-1 strain isolated in Germany. However the Cap protein of a PCV-1 isolated in France from a pig co-infected by PCV-1 and PCV-2 does not interact with gC1qR.

The differential interaction of gC1qR with the Cap proteins of pathogenic and non-pathogenic strains may explain their virulence. Future works will determine the importance of the interaction of gC1qR with Cap proteins during the cell infection by porcine circoviruses.

Disclosure of Interest: None Declared.