Endothelial Cells Are Main Producers of Interleukin 8 through Toll-Like Receptor 2 and 4 Signaling during Bacterial Infection in Leukopenic Cancer Patients

Abstract

Cancer patients who are leukopenic due to chemotherapy are susceptible to bacterial infections. Normally, clinical conditions during bacterial infections are caused by pathogen-associated molecular patterns, which are components that bind to Toll-like receptor (TLR) 2 (TLR-2) and TLR-4 on leukocytes, resulting in the production of inflammatory cytokines. The mechanism of this inflammatory response in cancer patients with diminished numbers of leukocytes is not completely clear. The levels of interleukin 1␤ (IL-1␤) and tumor necrosis factor alpha measured in the circulation of leukopenic cancer patients are lower than those measured in that of nonleukopenic patients during bacterial infections, whereas plasma interleukin 8 (IL-8) levels show distinct identical increases during bacterial infections in both leukopenic and nonleukopenic patients. Normally, these cytokines are mainly secreted by leukocytes. In cancer patients with bacterial infections and a diminished number of leukocytes, other sources of IL-8 production, such as endothelial cells, might be expected. Endothelial cells instead of leukocytes become the most important producers of IL-8 during bacterial infections in patients with chemotherapy-induced leukopenia through TLR-2 and TLR-4 signaling. Whole blood samples from six cancer patients were stimulated with lipopolysaccharide (LPS), and then IL-8 concentrations in supernatants were measured. Further, human umbilical vein endothelial cells (HUVECs) were incubated with sera from leukopenic cancer patients with or without bacterial infections, and then IL-8 concentrations in supernatants were measured (n ‫؍‬ 6). In addition, the same HUVEC experiment was performed with the addition of neutralizing antibodies against TLR-2 and TLR-4. During leukopenia (<10 9 cells/liter), LPS stimulation of whole blood did not result in an increase in IL-8 levels. However, when endothelial cells were incubated with sera from leukopenic cancer patients during bacterial infections, a threeto eightfold increase in IL-8 production was found, compared to the IL-8 production found after incubation with sera from patients without signs of infections. This increase did not reflect a higher level of IL-8 already present in the sera. Further, we demonstrated that IL-8 production induced in endothelial cells by sera from patients with documented gram-negative infections could be reduced significantly by up to 40% when the cells were incubated with neutralizing antibodies against TLR-4 (P ‫؍‬ 0.028). The addition of TLR-2 antibodies slightly enhanced the reduction of IL-8 production. These results suggest that during bacterial infections in cancer patients with markedly diminished numbers of leukocytes, endothelial cells become important producers of IL-8 through TLR-4 signaling and, to a lesser extent, TLR-2 signaling.

Inflammatory response to mucosal barrier injury after myeloablative therapy in allogeneic stem cell transplant recipients

“…This might be a result of endothelial cells or surviving immune effector cells responding to invading bacteria. 14 However, only 11 patients developed OVS bacteraemia and although CRP, IL-8 and LBP concentrations were already increased before the onset of OVS bacteraemia they were not different from those of patients who did not develop bacteraemia. Markedly elevated LBP and CRP levels were also found by Levy et al 15 1 week after transplant among paediatric SCT recipients with endotoxaemia, not bacteraemia, being found in four,that is, a third of the 14 patients on the day of transplant.…”

Bacteraemia coincides with low citrulline concentrations after high-dose melphalan in autologous HSCT recipients

“…27 Endothelial cells, such as the epithelial cells of the gut, play an important part in the innate immune system in neutropenic patients and produce IL-8 when exposed to bacteria. 28 Hence, perhaps monitoring IL-8 levels 29,30 combined with the MASCC risk score, when patients have low citrulline concentrations, might help distinguish those at risk of developing bacteraemia from those who are not.…”

Heterogeneity in lipopolysaccharide responsiveness of endothelial cells identified by gene expression profiling: role of transcription factors

“…Based on previous findings that serum IL-8 concentration is associated with severity of sepsis [16,18,19], and the fact that IL-8 is produced strongly by endothelial cells [20,21], endothelial cells were grouped according to their IL-8 production. The following questions were then raised: (1) is low IL-8 production associated with low production of other mediators, (2) if so, what are these mediators and (3) what is the molecular basis for this phenomenon?…”