The biological mechanisms in neutrophil and eosinophil adhesion and transmigration in vitro and theur relation to the inflammatory process in vivo

In inflammatory reactions, eosinophils and neutrophils constitute the major classes of granulocytes that emigrate from the bloodstream into the tissues. The recruitment of inflammatory cells constitutes a multi-step process that includes sequential adhesion and transmigration through, the endothelial lining, the underlying basement membrane and a variety of extracellular matrix components. This thesis examines the adhesion and transmigration properties of neutrophil and eosinophil during different inflammatory processes.

We have investigated the in vitro effect of eotaxin on human peripheral blood eosinophils (PBE) with respect to CD11b/CD18 expression and adhesion properties to the matrix protein fibronectin. We demonstrate that eotaxin is involved in the quantitative up-regulation of CD11b/CD1 8 expression and increases the adhesion properties in primed, but not resting, human eosinophils. We hypothesise that eotaxin and IL-5, but not MP, act synergistically in these respects.

The adhesion and transmigration assays were set up to simultaneous analysis of eosinophil and neutrophil adhesion and transmigration in mixed granulocyte cell populations, based on analysis of eosinophil cationic protein (ECP) and myeloperoxidase (WO) as markers for eosinophils and neutrophils, respectively. These models can be useful tools in exploring the mechanisms whereby neutrophils and eosinophils integrate chemotactic signals, communicate and to evaluate the impact of this communication on the overall leukocyte accumulation at disparate inflammatory sites.

We examined the capacity of circulating neutrophils, collected before, during and after hemodialysis with cuprophan, low- and high-flux polysulfone dialyzers, to transmigrate through a fibronectin covered membrane in vitro. The high-flux polysulfone treatment, as opposed to low-flux and cuprophan dialyzers, ameliorates the transmigration properties of circulating neutrophils, despite similar effects on adhesion molecule phenotypes.

Eosinophils in the neonatal period possess an enhanced responsiveness against the bacterialrelated peptide MP, as judged by enhanced transmigration capacity and CD11b upregulation, presumably due to the ability to express the fMLP receptor. We therefore suggest that eosinophils in the neonatal period represent a first line of cellular defence that might be triggered by bacterial antigen stimulation initiated by the early colonisation of the surfaces of the mucosa.

We demonstrate that PBE in allergic, but not in healthy children possess an increased spontaneous, as well as eotaxin-induced capacity to transmigrate in vitro. This increased capacity is further enhanced within 2 hours after an allergen challenge in vivo without accompanying signs of eosinophil activation in terms of increased PBE counts or ECP levels. These observations are probably related to the phenomenon designated "priming".