Influence of Bacterial Endotoxin on Radiation-Induced Activation of Human Endothelial Cells in Vitro and in Vivo

Abstract

Previous work from our group has contributed to demonstrate the role of conditioning related release of proinflammatory cytokines in induction of acute graft-versus-host disease (GVHD) following allogeneic bone marrow transplantation (BMT). In the present report we show that ionizing radiation (IR) in a clinical relevant dose upregulates intercellular adhesion molecule 1 (ICAM-1) on cultured human microvascular endothelial cells (HMEC). Bacterial endotoxin (lipopolysaccharide, LPS) in a concentration corresponding to serum levels seen during clinical endotoxemia, is capable of further enhancing ICAM-1 expression on irradiated cells. Adhesion assays with freshly isolated peripheral blood mononuclear cells (PBMC) revealed that increased ICAM-1 on IR-treated endothelial cells led to an increased adhesion of PBMC. Again, this effect could be superinduced by LPS. Recombinant human interleukin 10 (IL-10), an antagonistic cytokine known to function as an LPS antagonist, was able to counteract the LPS-mediated enhancement of IR-triggered ICAM-1 induction and PBMC adhesion. In contrast, IL-10 could not inhibit irradiation caused effects. IL-10 seemed to interfere with the translocation of preformed intracellular ICAM-1 to the cell membrane. To investigate whether this superinductive function of IR and LPS on endothelial cells is of clinical relevance, mice were treated with total body irradiation (TBI) and inoculated with a single dose of LPS. Immunohistochemical analyses of murine tissues demonstrated that LPS superinduces IR-triggered ICAM-1 also in vivo. These findings may be of clinical importance as they suggest that the endothelium is activated after radiotherapy or TBI used for conditioning in bone marrow transplantation. The activated endothelium in turn may facilitate the accumulation of effector cells at sites of inflammation.

Predicting the severity of graft-versus-host disease from interleukin-10 levels after bone marrow transplantation

“…4,7 These properties of IL-10 have led to its use for the treatment of GVHD in several studies, since IL-10 inhibits the activity of antigen-presenting cells and reduces the proliferation of lymphocytes as well as antagonizing lipopolysaccharide, which is involved in the production of inflammatory cytokines. 8,9 However, treatment with IL-10 did not effectively suppress GVHD in these studies and actually aggravated it in some cases, resulting in a poor prognosis because treatment with this cytokine caused rejection. 10,11 We interpreted the results obtained in the present study as follows.…”

Prognostic significance of increased IL-10 production in patients prior to allogeneic bone marrow transplantation

“…High levels of IL-10 produced prior to BMT may down-regulate tissue expression of ICAM-1 and ICAM-1-mediated transendothelial migration of inflammatory cells which occurs after irradiation or LPS activation. 17,18 In addition, downmodulation of other costimulatory molecules including CD80 on antigen presenting cells such as dendritic cells by IL-10 may result in tolerance. 19 Finally, presence of high IL-10 production at the time of donor cell infusion might induce a host-specific anergic state in donor T lymphocytes as reported in vitro in mixed lymphocyte reactions carried out in the presence of IL-10.…”

Accumulation of CD4+T cells in the colon of CsA-treated mice following myeloablative conditioning and bone marrow transplantation

“…Numerous studies have shown the important role of CAMs in lymphocyte homing to inflamed tissues (2,10,21,22,27,45). Since our studies concentrated on the colon, we focused on the expression of MAdCAM, because it has been demonstrated to be essential in the induction of intestinal GVHD (22).…”

“…Irradi- ation has also been shown to stimulate macrophage production of proinflammatory cytokines in a dose-dependent manner (43). Several in vivo and in vitro studies have demonstrated that endothelial cells respond to stimuli such as irradiation, LPS, and TNF-␣ by becoming activated or undergoing apoptosis (21,40). In the SGVHD model, increased bacterial leakage into the liver was observed during CsA therapy, suggesting increased permeability of the colon in these animals (25).…”

“…Radiation therapy is capable of disrupting the epithelial integrity, leading to an inflammatory response and, hence, increased expression of proinflammatory cytokines and chemokines (12,21,40). The constitutive presence of these regulators allows for the trafficking of lymphocytes into the GI mucosal compartment, disrupting the physiological balance and contributing to pathogenesis such as IBD (31,41).…”