In sepsis, monocytes exhibit the differential immune response states of ‘priming’ (increased responsiveness to secondary stimuli) and ‘deactivation’ (reduced responsiveness, depressed expression of HLA-DR and CD86, increased PDL-1), which may reflect the opposing hyperinflammatory and immune-suppressive systemic conditions. In an era where the number and phenotype of circulating leucocytes are used to guide sepsis immune therapy investigation, there is debate as to whether sepsis immunity is differentially regulated within the blood and tissue compartments of the body. Adding to this uncertainty is the fact that core support therapies, such as vasopressor resuscitation, may have an immunomodulatory effect during sepsis.
We hypothesised that monocytes undergo trans-endothelial reprogramming during migration between vascular and tissue compartments and that this is a crucial determinant of sepsis immunity and its clinical monitoring. Further, we hypothesised that noradrenaline and vasopressin have a role in the functional and phenotypic modification of monocytes during sepsis. Our aims were to 1) develop an in-vitro model of priming and deactivation using healthy volunteer (HV) monocytes; 2) to test the direct effects of noradrenaline and vasopressin on monocytes in comparison to sera from the VAsopressin versus Noradrenaline as Initial therapy in Septic sHock (VANISH) trial; 3) develop a human lung microvascular endothelial cell (HLMVEC) transwell model of monocyte migration and associated phenotypic changes during sepsis.
The major findings of this work were that in combination vasopressin and noradrenaline suppressed LPS-induced TNF release in non-pretreated and primed HV monocytes. In contrast, when HV monocytes were incubated with VANISH patient sera we found no difference
in surface marker expression or LPS-induced TNF release. Conditioning of monocytes with vasopressin or noradrenaline was found to enhance their migration in an uncoated transwell assay. Lastly, we successfully developed an HLMVEC-coated transwell migration assay able to detect changes in pre- and post-migration monocyte phenotype.