Timothy B. McPherson

Xenogeneic extracellular matrix grafts elicit a TH2-restricted immune response1

Background. Porcine small intestinal submucosa (SIS) is an acellular, naturally derived extracellular matrix (ECM) that has been used for tissue remodeling and repair in numerous xenotransplantations. Although a vigorous immune response to xenogeneic extracellular matrix biomaterials is expected, to date there has been evidence for only normal tissue regeneration without any accompanying rejection. The purpose of this study was to determine the reason for a lack of rejection. Methods. Mice were implanted s.c. with xenogeneic tissue, syngeneic tissue, or SIS, and the graft site analyzed histologically for rejection or acceptance. Additionally, graft site cytokine levels were determined by reverse transcriptase polymerase chain reaction and SIS-specific serum antibody isotype levels were determined by ELISA. Results. Xenogeneically implanted mice showed an acute inflammatory response followed by chronic inflammation and ultimately graft necrosis, consistent with rejection. Syngeneically or SIS implanted mice, however, showed an acute inflammatory response that diminished such that the graft ultimately became indistinguishable from native tissue, observations that are consistent with graft acceptance. Graft site cytokine analysis showed an increase in interleukin-4 and an absence of interferon-&ggr;. In addition, mice implanted with SIS produced a SIS-specific antibody response that was restricted to the IgG1 isotype. Reimplantation of SIS into mice led to a secondary anti-SIS antibody response that was still restricted to IgG1. Similar results were observed with porcine submucosa derived from urinary bladder. To determine if the observed immune responses were T cell dependent, T cell KO mice were implanted with SIS. These mice expressed neither interleukin-4 at the implant site nor anti-SIS-specific serum antibodies but they did accept the SIS graft. Conclusions. Porcine extracellular matrix elicits an immune response that is predominately Th2-like, consistent with a remodeling reaction rather than rejection.

Galα(1,3)Gal Epitope in Porcine Small Intestinal Submucosa

Small intestinal submucosa (SIS) is a naturally occurring, acellular biomaterial derived from porcine jejunum, which promotes constructive tissue remodeling when applied as a xenogeneic graft mater...

The Th2-Restricted Immune Response to Xenogeneic Small Intestinal Submucosa Does Not Influence Systemic Protective Immunity to Viral and Bacterial Pathogens

Implantation of mice with xenogeneic extracellular matrix (ECM) not only results in tissue remodeling but also elicits a strong Th2 immune response. It is possible that the Th2 cytokines induced by ECM act systemically and result in immune suppression to unrelated antigens. In this case, the recipient would be predisposed to immune dysfunction and have increased susceptibility to various pathogens. The purpose of this study was to determine if ECM implantation does, in fact, influence the immune response to other antigens. Four models were examined to determine the effects of ECM implantation on systemic immunity. In the first model, mice were subcutaneously implanted with porcine small intestinal submucosa (SIS) and immunized with a T-dependent subunit vaccine against influenza virus. The antibody response and protection against lethal infection were then measured. The second model consisted of similar experiments performed using a T-independent polysaccharide vaccine against S. pneumoniae. In the third model, mice were implanted and the cell-mediated response to dinitrofluorobenzene (DNFB) challenge was determined. The fourth model involved examining the influence of SIS implantation on rejection of xenogeneic skin grafts. We found that antibody levels of mice vaccinated against influenza virus or S. pneumoniae were not affected by SIS implantation and these mice did not exhibit increased or decreased susceptibility to either infectious agent. Similarly, mice implanted with ECM showed no cell-mediated immune dysfunction upon challenge with DNFB or xenogeneic skin grafts. The results of this study demonstrate that the Th2-restricted response induced by xenogeneic ECM implantation does not cause generalized immune suppression. Therefore, SIS implantation does not increase susceptibility to viral or bacterial pathogenic agents.

Grafting of PEO to Glass, nitinol, and pyrolytic carbon surfaces by γ irradiation

Glass, nitinol, and pyrolytic carbon surfaces were grafted with poly(ethylene oxide) (PEO) and PEO-containing Pluronic® surfactants by γ irradiation. These substrates were coated with a primer layer of trichlorovinylsilane (TCVS), which allows grafting of organic polymers. The TCVS-coated substrates were adsorbed with PEO or Pluronics® and exposed to 0.3 Mrad of γ radiation to graft the polymer to the surface. PEO-grafted substrates were characterized by contact angle measurement, X-ray photoelectron spectroscopy, fibrinogen adsorption, and platelet adhesion and activation. Surface modification with PEO reduced fibrinogen adsorption by as much as 99%. Platelet adhesion was significantly reduced or prevented on the modified surfaces. Protein- and platelet-resistance effects were independent of hydrophilicity of the PEO-grafted surfaces. Polymer grafting by γ radiation to TCVS-coated substrates provides a facile process to improve thromboresistance of inorganic biomaterials.