Tissue distribution of CD6 and CD6 ligand in cattle: expression of the CD6ligand (CD166) in the autonomic nervous system of cattle and the human

We studied the tissue distribution of CD6(+) lymphocytes and cells expressi ng the CD6 ligand (also known as activated leukocyte cell adhesion molecule CD166) in calves by immunohistochemistry using an anti-bovine CD6 monoclon al antibody (mAb), a human CD6 (huCD6)-immunoglobulin G1 fusion protein. (h uCD6-Ig), and an anti-human CD166 (anti-huCD166) mAb, The huCD6-Ig and anti -huCD166 mAb bound to the sympathetic and parasympathetic nerve fibers but not to myelinated nerve fibers in the spinal nerve. Studies with human tiss ue using the anti-huCD166 mAb yielded identical patterns of labeling. Dense accumulations of CD6(+) lymphocytes were present in areas of the thymuses and spleens of calves, in areas innervated by huCD6-Ig(+) nerves. The cDNAs encoding the bovine CD166 and CD6 were isolated from the sym-pathetic gang lion and spleen, respectively. Predicted amino acid residues that are impor tant for human and mouse CD6-CD166 binding were also conserved in bovine CD 6 and CD166, Bovine CD166 transcripts were detected by reverse transcriptas e-PCR in all the tissues that bound huCD6-Ig, These results show that the b ovine orthologue of CD166 was constitutively expressed in the autonomic ner vous systems of cattle and suggest that CD6(+) lymphocytes adhere to CD166( +) autonomic nerve terminals via CD6.