Many immunological experiments would be greatly facilitated if peripheral blood mononuclear cells (PBMC) preserved important functional properties over longer periods of time. Regarding adhesive interactions with endothelial cells, a crucial step of inflammatory processes, this had not been investigated yet. We demonstrate that PBMC subsets subjected to controlled cryopreservation retain their phenotypic traits inasmuch as the proportion of viable T cells, monocytes/macrophages and B cells was comparable with their freshly isolated counterparts. More importantly, we demonstrate for the first time that the procedure does not impede crucial adhesion-mediated dynamic interactions with endothelial cells. Using a flow chamber system, freshly isolated and cryopreserved PBMC showed similar rolling and firm adhesion on TNF-a-activated endothelial cells under shear flow as compared to freshly isolated PBMC from the same donors. Thus, our observation is an important prerequisite for functional studies of leucocyte recruitment when sequential investigations with material from the same patients are required.Key words: endothelial cell -leukocyte rolling -method for preserving PBMC functions
Accepted for publication 20 February 2013Peripheral blood mononuclear cells (PBMC) are indispensable for many immunological analyses, both in basic and clinical research. Long-term or repeated studies require PBMC storage while reliably preserving functional traits. Since the first successful preservation of mouse lymphocytes (1), different freezing protocols have been developed. Phenotypic traits of lymphocytes remained stable after freezing at À80°C, while monocytes, macrophages and granulocytes were more prone to damage (2). Programmed freezing and mechanical freezing methods appeared to be comparable regarding recovery and viability of PBMC (3). Concerning apoptosis, storage of PBMC at À150°C was superior compared to storage at À30°C or to storage of whole-blood samples at either temperature (4,5).Notwithstanding a fair number of approaches to store PBMC, we were surprised to find that virtually all of these earlier studies had a peculiar view on a limited array of cellular functions or mere phenotypic characterization (5-7). Thus, the capability of cryopreserved PMBC to properly interact with endothelial cells, a crucial early step in inflammatory reactions, still had to be established. Using a dynamic flow chamber system, we provide here the first experimental evidence for intact functional traits of PBMC after cryopreservation regarding rolling on and adhesion to cultured endothelial cells.Towards this end and with ethical approval, venous blood (20-40 ml) was collected from a total of six healthy volunteers (five female non-smokers, one male smoker; age range 22-28 years). PBMC were isolated using Ficoll-Paque PLUS density gradient centrifugation and washed with Hank's buffered salt solution (HBSS). PBMC were labelled with carboxyfluorescein diacetate succinimidyl ester (CFSE, 2 lM in HBSS) for flow chamber analysis dir...