Cross-species costimulation: relative contributions of CD80, CD86, and CD40.

BACKGROUND: The response of human CD4+ T cells against porcine cells is of comparable magnitude to that induced by human leukocyte antigen-mismatched allogeneic cells. This reflects productive interactions between key costimulatory molecules across the species barrier. Inhibition of these molecular interactions will be crucial in overcoming CD4+ T-cell-mediated rejection of xenografts. We have performed a detailed investigation to determine the expression profiles and relative contributions of the three key costimulatory molecules in the porcine-human xenogeneic response. Whereas only porcine CD86 is constitutively expressed on resting endothelial cells, both CD40 and CD80 are rapidly expressed after activation. All three costimulatory molecules are expressed by professional antigen-presenting cells. METHODS: We have isolated full-length cDNA clones for human and porcine CD80, CD86, and CD40. Human fibroblast cell lines (M1) coexpressing DR1 were transfected with these cDNAs and used in mixed lymphocyte reactions and flow cytometric studies in vitro. RESULTS: These data provide the first characterization of the expression profile and functional role of porcine CD80. Functional assays demonstrate that pCD40, pCD80, and pCD86 are independently capable of costimulating human CD4+ T cells, albeit with differing kinetics. Proliferative responses were of comparable magnitude to those obtained when costimulation was provided by human CD40, CD80, and CD86. CONCLUSIONS: These data have implications for therapy targeting the direct pathway of xenorecognition; costimulatory molecule blockade must be directed against both the B7/CD28 and CD40/CD40L pathways.

Cytohesins and centaurins control subcellular trafficking of macromolecular signaling complexes: regulation by phosphoinositides and ADP-ribosylation factors.

The ADP-ribosylation factor family of small GTP-binding proteins are implicated in the regulation of vesicular transport and control of cytoskeletal and cell adhesion events. The phosphoinositide 3-kinase, phosphoinositide 4-P 5-kinase and phospholipase D signaling pathways are major regulators of ARF signaling cascades. Two families of ARF regulatory molecules, the cytohesin ARF-Guanine nucleotide Exchange Factors and the centaurin GTPase-Activating Proteins provide key targets for the action of these lipids signals. A critical feature of the regulation of ARF signaling is coordinated recruitment of exchange factors, ARFs and GAPs to appropriate subcellular locations. These complexes drive repetitive cycles of ARF activation and membrane association that underlie the processes of cell movement as well as endosomal uptake and intracellular redistribution of signaling molecules. Cytohesins and centaurins bind specifically to a variety of other signaling proteins and these interactions may provide routes for regulated recruitment to the sites of ARF activation. Through their ability to control endosomal trafficking/recycling of these supramolecular signaling complexes ARF and phospholipid signaling pathways may have consequences that reach as far as the regulation of gene transcription and control of cell fate.

Cytohesins and centaurins control subcellular trafficking of macromolecular signaling complexes: regulation by phosphoinositides and ADP-ribosylation factors

The ADP-ribosylation factor family of small GTP-binding proteins are implicated in the regulation of vesicular transport and control of cytoskeletal and cell adhesion events. The phosphoinositide 3-kinase, phosphoinositide 4-P 5-kinase and phospholipase D signaling pathways are major regulators of ARF signaling cascades. Two families of ARF regulatory molecules, the cytohesin ARF-Guanine nucleotide Exchange Factors and the centaurin GTPase-Activating Proteins provide key targets for the action of these lipids signals. A critical feature of the regulation of ARF signaling is coordinated recruitment of exchange factors, ARFs and GAPs to appropriate subcellular locations. These complexes drive repetitive cycles of ARF activation and membrane association that underlie the processes of cell movement as well as endosomal uptake and intracellular redistribution of signaling molecules. Cytohesins and centaurins bind specifically to a variety of other signaling proteins and these interactions may provide routes for regulated recruitment to the sites of ARF activation. Through their ability to control endosomal trafficking/recycling of these supramolecular signaling complexes ARF and phospholipid signaling pathways may have consequences that reach as far as the regulation of gene transcription and control of cell fate