Two related ligands of the TNF family, BAFF and APRIL, in rabbit: molecular cloning, 3D modeling, and tissue distribution.

B-cell activating factor belonging to the TNF family (BAFF) and a proliferation-inducing ligand (APRIL) are two related members of the TNF ligand superfamily. These two ligands and their receptors, also termed "the BAFF/APRIL system", play important immunological roles, especially in the B-cell arm of the immune system. This paper reports the cloning and expression analysis of these two cytokines in rabbit (Oryctolagus cuniculus) by homology cloning. The complete transcript of the rabbit BAFF was sequenced and contained 1457 bp, including an 873 bp open reading frame. The predicted protein of 290 aa revealed the presence of the BAFF family signature, the "Flap". The soluble mature part of rabbit BAFF (sBAFF) showed 75-92% sequence identity with mammalian and avian homologs. The full-length cDNA of rabbit APRIL contained 1030 bp of which 753 bp are the open reading frame. The conserved potential N-glycosylation site and the cysteine residues were found in both the two ligands. The predicted three dimensional (3D) structures of sBAFF and sAPRIL analyzed by comparative protein modeling reveal that they are very similar to the human counterparts. Real-time PCR analysis revealed that rabbit BAFF gene was predominantly expressed in the lymphoid tissues, such as spleen and thymus; while the APRIL mRNA was found to be relatively high in a wide range of tissues. These findings indicate that BAFF and APRIL in rabbit play similar roles as in human. It provides the basis for investigation on their roles in regulating B-cell development and immune responses in rabbit and also contributes to our understanding of the evolution of these two novel TNF ligands.