Human TNF Can Induce Nonspecific Inflammatory and Human Immune-Mediated Microvascular Injury of Pig Skin Xenografts in Immunodeficient Mouse Hosts

Abstract

TNF activates endothelial cells to express cell surface molecules that are necessary to recruit a local infiltrate of leukocytes. Because the actions of this proinflammatory cytokine are not species restricted, we investigated whether human TNF can up-regulate porcine endothelial adhesion molecules to elicit human T cell infiltration and damage of pig skin xenografts in a chimeric immunodeficient mouse model. We have previously demonstrated the vigorous rejection of human skin allografts and the absence of injury to porcine skin xenografts in human PBMC-SCID/beige mice. Intradermal administration of human TNF at high doses (600 or 2000 ng) caused nonspecific inflammatory damage of pig skin grafts, whereas low concentrations of TNF (60 or 200 ng) resulted in human PBMC-dependent injury of porcine endothelial cells. There was a strong correlation among pig skin xenograft damage, human T cell infiltration, and the TNF-induced up-regulation of swine MHC class I and class II molecules, VCAM-1, and, in particular, the de novo expression of porcine E-selectin. The microvascular damage and leukocytic infiltration elicited by TNF were enhanced by porcine IFN-γ, suggesting that xenografts may be less prone to cytokine-mediated injury due to the species-restricted effects of recipient IFN-γ. Our results indicate that maintenance of a quiescent endothelium, which does not express E-selectin or other activation-dependent adhesion molecules, is important in preventing human anti-porcine T cell xenoresponses in vivo and that TNF signaling molecules and TNF-responsive gene products are appropriate therapeutic targets to protect against human T cell-mediated rejection of pig xenografts.

Effect of Redox Modulation on Xenogeneic Target Cells: The Combination of Nitric Oxide and Thiol Deprivation Protects Porcine Endothelial Cells from Lysis by IL-2-Activated Human NK Cells

“…In the present study, we confirmed that human TNF-␣ increased the expression of E-selectin and, to a lesser extent, VCAM-1, expression by PAEC, suggesting that PAECs are activated by human TNF-␣ to express certain adhesion molecules, consistent with previous reports (46,49). Importantly, TNF-␣-activated PAECs were more susceptible to lysis by IL-2-activated human NK cells compared with nonstimulated PAEC, implicating EC activation, and possibly expression of adhesion molecules, E-selectin, in particular, in their increased vulnerability to lysis mediated by IL-2-activated human NK cells.…”

“…Evidence has shown that TNF-␣, a cytokine that is active across species, is produced by cells that infiltrate rejecting xenografts (48) and human TNF-␣ can activate porcine EC when transplanted into immunodeficient mice (49). Therefore, TNF-␣ would be expected to be an important factor in vivo in determining xenograft survival.…”

“…Because TNF-␣ activates EC to produce and express adhesion molecules (46,49,53), we analyzed the expression of E-selectin and VCAM-1 on the surface of PAEC under conditions of oxidative stress with and without pretreatment with SNAP (Fig. 2).…”

The Cathepsin B Death Pathway Contributes to TNF Plus IFN-γ-Mediated Human Endothelial Injury

“…Cytokines are important effectors of tissue injury in addition to serving as mediators of inflammatory responses (1). Combined treatment of TNF and IFN-␥ induces significant EC injury in vivo, even when both TNF and IFN-␥ are present at low concentrations (41). TNF and IFN-␥ are often present in combination during pathophysiological conditions such as sepsis (2).…”

Membrane markers of the immune cells in swine: an update

“…It is recognised by the human cross-reacting mAb 12B6 [105,224]. It is expressed on the activated vascular endothelium, and mediates attachment of neutrophils, monocytes and some lymphocytes [27,112,224].…”