To investigate the role of sIgM playing in the infection process of infectious bursal disease virus(IBDV),the interactions between sIgM λ light chain and IBDV was systematically studied by using DT40,a sIg M-bearing cell line derived from chicken busal lymphoma.The experiments of protein expression,VOPBA,virus binding and binding inhibition were performed to evaluate the binding abilities of DT40 cells and sIgM λ light chain to IBDV particles.VOPBA showed that the λ light chain of sIgM specifically interacted with 4 distinct strains of IBDV in a virulence independent manner.Flow cytometric analysis also showed that more than half of DT40 cells bound IBDV particles,and the binding was efficiently inhibited by sIgM-specific monoclonal antibody(mAb) L1.Our data indicates that sIgM λ light chain plays as an important site for the binding of IBDV,which provided some important clues for the further investigations of the molecular pathogenesis of IBDV infection to B lymphocytes using DT40 as the target cell model.

The λ light chain of sIgM was cloned by RT-PCR from the total cellular RNAs of DT40 cells. DNA sequencing showed that the λ light chain of sIgM was 852 nt long including an 657 nt open reading frame (ORF) and 195 nt 3'-UTR. The sequence homology between DT40 sIgM λ light chain and chicken Ig λ light chain was 95 % at nucleotide level and 92.6 % in deduced amino acids. The PCR product was cloned into prokaryotic expression vector pET-28a for expression. SDS-PAGE analysis showed that the λ light chain of sIgM was abundantly expressed in E.coli BL21 (DE3). The present study provided foundation for further investigation on the role of sIgM in the infection process of IBDV to B-lymphocytes.