High sequence homology between human and pig CD40 with conserved binding to human CD154.
BACKGROUND
Understanding the molecular interactions between pig tissues and human immune cells is fundamental to achieving long-term pig to human xenograft survival. CD40 has been shown to be central in the interaction of T cells with many antigen-presenting cells including B cells, and dendritic cells. It has been clearly shown in vitro that human T cells can effectively recognize pig major histocompatibility complex proteins, and that various accessory molecule interactions are compatible between these species, including human CD28 with pig B7 family members (CD80/CD86). The importance of CD40 in transplantation has been established using blocking antibodies to its ligand, CD154, which prolong allograft survival in mouse and primate models.


METHODS
Pig CD40 was cloned from a porcine spleen cDNA library and subsequently sequenced. Expression of pig CD40 was detected by flow cytometry using soluble human CD154 (hCD154-Ig). Results. Comparison of the derived amino acid sequence of pig with human shows 74% identity. Significantly, there is conservation between pig and human at 5 residues shown by mutagenesis studies to be essential for binding of human CD40 to CD154. hCD154Ckappa was shown to bind pig B cell lines and a proportion of human and pig lymphocytes and further confirmed by staining of COS cells transfected with pig CD40. Conclusions. Recipient human cells bearing CD154 will, therefore, be able to bind donor pig CD40, and these interactions might modulate effector functions and hence influence xenograft survival. Further investigation is necessary to ascertain the exact nature of these interactions and their implications for xenograft survival.
Rushworth
S A
SA
Department of Surgery, University of Cambridge, United Kingdom.
Bravery
C A
CA
Thompson
S
S
D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology; D019013:CD40 Antigens / Q000235:genetics* / Q000276:immunology*; D023201:CD40 Ligand; D019556:COS Cells; D002460:Cell Line; D017124:Conserved Sequence / Q000235:genetics; D006801:Humans; D008214:Lymphocytes / Q000276:immunology; D008562:Membrane Glycoproteins / Q000276:immunology*; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D013552:Swine; D014162:Transfection
D019013:CD40 Antigens; D008562:Membrane Glycoproteins; D023201:CD40 Ligand