Background
Homeostasis and activation of immune cells is tidily regulated. A well organized response of different players of the immune system is evoked by disturbance of the steady state homeostasis as seen in e.g. case of inflammation or cancer. One of the major methodologies to study the interactions in the immune system specially in humans is the ex vivo analysis of monocytoid cells. This ex vivo analysis of human immune cells however might be hampered by the fact that these cells are particularly flexible in reacting to their environment. E.g. specialized cells such as macrophages or DC constantly monitor their environment via so-called pattern recognition receptors. Furthermore several factors present in vivo are removed in the ex vivo system. For peripheral blood mononuclear cells, some aspects of the response to the ex vivo culture conditions have been established. Monocyte adherence was regarded as an activating event resulting in changes of gene expression and protein secretion and mainly increase in IL8 expression was shown to result from adherence of PBMCs to plastic. We and others have recently demonstrated that blood asservation and cell isolation techniques have to be closely controlled when monitoring cellular responses on a global level. Here we asked the question whether there is a global cellular response to the ex vivo system itself. Gene expression profiling allows a large scale measurement of changes of gene expression and thereby an unbiased search of cellular changes.