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Expression of the cell adhesion molecule, L-selectin, on polymorphonuclear leukocytes during and after their release from the bone marrow

University of British Columbia

The emigration of polymorphonuclear leukocytes (PMN) to sites of inflammation requires a series of leukocyte-endothelial interactions which can be divided in four sequential steps. These include, tethering of flowing leukocytes; triggering or activation of leukocytes; firm adhesion to the endothelium and; emigration of leukocytes out of the vessels into inflamed tissue. The selectin family of adhesion molecules are involved in the tethering of leukocytes and one of these, L-selectin, is expressed on nearly all leukocytes including PMN. The recruitment of the PMN to sites of inflammation is highly dependent on the expression of this molecule on their cell surfaces. However, the role of L-selectin in the trafficking of the PMN from the bone marrow into the blood is less clear. The objective of this thesis was to determine the expression of L-selectin on PMN during their release from the bone marrow into the circulation and their eventual removal into the tissues. Immunocytochemical and immunohistochemical techniques were used to determine the expression of L-selectin on the PMN in cytological and histological specimens respectively. Indirect immunofluorescent flow cytometry was used to determine the expression of L-selectin on circulating PMN. Changes in L-selectin expression on PMN during their release from the bone marrow was studied during cardiopulmonary bypass in humans. These studies demonstrated that the expression of L-selectin on the mature segmented PMN in bone marrow is higher than on circulating PMN and that some of this L-selectin shed when PMN cross from the bone marrow hematopoietic compartment into the bone marrow venous sinusoids. However, L selectin expression on PMN in the venous sinusoids remains high and this results in an increased expression of L-selectin on circulating PMN during active bone marrow release. This means that circulating PMN expressing the highest levels of L-selectin, have been recently released from the bone marrow. A new method for labelling PMN in vivo using the thymidine analogue, 5’bromo-2-deoxyuridine was used to demonstrate that circulating PMN continuously lose L-selectin while they remain in the circulation. These studies explain the variable expression of L-selectin on the circulating PMN with the newly released PMN expressing the highest and the older PMN the lowest levels of L-selectin. This implies that the expression of L-selectin on circulating PMN is not just a marker of cell activation state, but also of cell age. This creates the opportunity to study the functional capabilities and the trafficking of different populations of the circulating PMN.

Thesis/Dissertation

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2009-06-05

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http://hdl.handle.net/2429/8810

Experimental Medicine

University of British Columbia

UBCV

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