CLONING AND CHARACTERIZATION OF THE BOVINE POLYMERIC IMMUNOGLOBULIN RECEPTOR-ENCODING CDNA

Trans-epithelial transport of polymeric immunoglobulins (pIg) into muc osal and glandular secretions is carried out by the pig receptor (pIgR ). Therefore, expression of the pIgR gene in epithelial cells of mucos al and glandular tissues is an absolute requirement for achieving muco sal immunity, We report the cloning and characterization of the bovine pIgR cDNA. Three overlapping cDNA clones with a total length of 3608 bp yielded an open reading frame encoding a 757-amino-acid (aa) transm embrane (TM) glycoprotein, Although polymorphism was found in two sepa rate clones, Northern blot analysis showed a single pIgR mRNA (approx. 3.8 kb) to be present in the mammary gland, liver, lung, kidney and i ntestine of a lactating cow. There was no detectable expression of pIg R in the spleen of the same animal. Comparison of the deduced bovine p IgR aa sequence with those of rat, mouse, man and rabbit shows that th is receptor is highly conserved both in aa sequence and structural org anization. The degree of conservation in the TM sequence and the C-ter minal cytoplasmic tail, which contains the various signals for intrace llular trafficking of the receptor, is 65-73%. We also find a high deg ree of conservation (61-66%) in the ectoplasmic part of the receptor, known as the secretory component (SC), with an exception for that of t he rabbit SC, which is much lower (47%). Among the five Ig-like domain s in the SC, the N-terminal domain I, where the primary pIg-binding si te is located, showed the highest (72-83%) aa sequence conservation.