Martijn D. de Kruif

Recent in vitro and murine in vivo studies have identified several potential LPS tolerance factors. In this study, we describe the expression kinetics of these LPS tolerance factors in standardized human endotoxemia models using i.v. LPS bolus administration. Responsiveness to LPS as well as the expression of potential regulators of LPS signaling were determined in peripheral whole blood. Intravenous LPS administration (4 ng/kg) resulted in peak plasma levels of TNF-alpha at 1.5 h followed by subsequent peaks of the classic negative feedback inhibitors A20 and IL-10 at 2 and 3 h, respectively. Circulating blood monocyte counts decimated during the initial inflammatory response, but normalized in the period between 4 and 8 h post-LPS. The LPS response as determined by ex vivo TNF release per monocyte in whole blood was profoundly decreased at 6-8 h post-LPS injection despite cessation of A20 and IL-10 expression after 4 h. Analysis of MyD88short, IL-1R-associated kinase (IRAK)-1, IRAK-M, ST2, suppressor of cytokine signaling-1 and -3, SHIP-1, and MAP kinase phosphatase-1 expression indicated that the observed LPS tolerance was associated with decreased IRAK-1 and elevated IRAK-M expression in this human model. Interestingly, a lower dose of LPS (1 ng/kg) induced LPS tolerance accompanied with IRAK-M up-regulation but without depletion of IRAK-1. In vitro studies in whole blood showed that IRAK-M up-regulation by LPS is largely dependent on TNF-alpha. The observed rise of IRAK-M transcription in the human endotoxemia model appeared much greater compared with in vitro-stimulated whole blood. In conclusion, LPS tolerance in human endotoxemia models is associated with IRAK-M up-regulation.

Infection with the human immunodeficiency virus (HIV) is still a major health problem world-wide. HIV infection has changed into a chronic infection with the chance of developing long-term complications. Vascular complications are frequently reported in the current literature. HIV and treatment by highly active antiretroviral therapy (HAART) are associated with many cardiovascular risk factors. An increased risk of arterial cardiovascular complications was found in a number of studies. However, data about the risk of venous thrombotic disease (VTE), including potentially fatal conditions as pulmonary embolism, were limited. In a systematic review of the literature, ten relevant epidemiological studies were identified that investigated the risk of venous thrombotic disease in HIV-infected patients. The incidence was increased two- to tenfold in comparison with a healthy population of the same age. However, these studies were mainly retrospective cohort studies that were prone to selection bias, confounding factors were not always mentioned and in all but three control populations were missing. An increased risk of venous thrombotic disease in HIV-infected patients could be explained by the presence of a hypercoagulable state, characterised by an increase in procoagulant factors, such as endothelial TF expression and thrombogenic properties of microparticles, and a decrease in anticoagulant factors, including AT III, HC II and the protein C pathway. Furthermore, the risk of VTE was associated with an increased risk of infections and autoimmune haemolytic anaemia, and was weakly associated with HAART. All together, quite some evidence pointed towards a relationship between HIV infection and venous thrombotic disease, but the association still needs to be established in properly designed epidemiological studies.