Responsiveness of human circulating phagocytes in relation to the inflammatory condition

Abstract

In the early stages of the inflammatory process, monocytes and granulocytes constitute important effector cells that must function correctly in order to clear infection. By activating leukocytes in vitro it is possible to mimic the in vivo activation of these cells and study their activation potential. However, in vitro activation may not tell the entire story: cells that have been exposed to inflammatory mediators in vivo could have an altered response when activated in vitro. The objective of this thesis was to evaluate the functional response, with different activation markers, of peripheral granulocytes and monocytes, in relation to selected inflammatory conditions.

Peripheral leukocytes from blood donors are frequently used as control cells in laboratory tests. It is known that blood sampling and separation techniques can affect the quantitative levels of activation markers on leukocytes. In the first study we therefore investigated the influence of two different blood sampling procedures, in a blood donation setting, on peripheral granulocytes. We found that a brief contact with the transfer tube generated an ex vivo activation of peripheral neutrophils probably due to activation of the complement system within the transfer tube.

During coronary artery bypass grafting (CABG) a whole body inflammatory response occurs, and the heart-lung machine (CPB) has been thought to be the major contributor to this phenomenon. In the second and third part of this thesis we evaluated the impact of the CP13 on peripheral phagocytes during CABG. Patients were randomised to surgery with (ONCAB) or without (OFFCAB) CPB. We could demonstrate less complement activation in OFFCAB compared to ONCAB patients during and 24 hours after CABG surgery.

Despite this finding, both neutrophil and monocyte adhesion molecule expression was similar for both patient groups. The cells responsiveness to in vitro activation was also similar. Neutrophil numbers increased during and after CABG surgery whereas the number of circulating eosinophils decreased considarably. We also found a selective decrease in the numbers of CD14+/CD16+ monocytes during surgery. Both neutrophils and monocytes are activated as a consequence of CABG without apparent additional effects of CPB. The investigated parameters indicate that the surgical trauma could be the most important factor contributing to the enhanced inflammatory response noted during cardiac surgery.

In the last part of the study we investigated the systemic influence of a chronic inflammatory condition, namely chronic obstructive pulmonary disease (COPD), on peripheral blood phagocytes. We found that neutrophils, monocytes and eosinophils from both COPD patients and asymptomatic smokers have an impaired oxidative burst in vitro compared to those from non-smokers. In addition patients and smokers also have vascular involvement as determined by elevated levels of sICAM1. There were no differences in adhesion molecule expression or mobilisation between the studied groups although smoking had an acute effect on CD 11 b mobilisation in COPD patients. These findings may in part explain why COPD patients show increased susceptibility to respiratory infections.

Taken together, the data presented in this thesis demonstrate the value of monitoring peripheral granulocytes and monocytes during acute and chronic inflammatory disorders. In vitro activation is a helpful tool for examining the responsiveness of circulating phagocytes.