The role of flow cytometry in improving biocompatibility in transfusion medicine

Platelet function testing in apheresis products: flow cytometric, resonance thrombographic (RTG) and rotational thrombelastographic (roTEG) analyses

During storage of platelet concentrates, quality control of the units is mandatory. This includes the important testing of the hemostatic function of platelets. So far, mostly platelet aggregation analyses have been performed. In this study, new approaches were tested to evaluate the applicability of modern techniques for quality monitoring. Plateletpheresis was performed with two different cell separators (AMICUS cell separator, Fenwal, Baxter Healthcare, Deerfield, USA; COBE Spectra, COBE BCT, Lakewood, USA). In each procedure split products (n = 22) were prepared and stored for 1-2 days (n = 22) or 3 5 days (n = 22). Platelet hemostatic capacity was tested by applying flow cytometry. platelet aggregation (platelet-rich-plasma [PRP]+agonist), resonance thrombography (RTG; PRP, no agonist) and rotational thrombelastography (roTEG; PRP+agonist). Flow cytometric analyses did not reveal significant changes in structural (CD41a. CD42b) or activation-dependent antigens (CD62p, CD63, LIBS, RIBS). Also, differences in the data from the flow cytometric reactivity tests were not significant between the two groups. In platelet aggregation assays, shape change (p = 0.8), maximum aggregation (p = 0.4), and maximum gradient (p = 0.8) did not show significant differences between the two groups. In the RTG test, differences between r-time (reaction time; p = 0.4), and f-time (clot formation time [fibrin influence]; p = 0.3), and in roTEG r-time (coagulation time; p = 0.1) and k-time (clot formation time; p = 1.0) were not significant. P-time (clot formation time [platelet influence]) and M (maximum amplitude) in RTG, and k-time and MA (maximum amplitude) in roTEG showed a slight decrease in platelet function (p < or = 0.05). We conclude that platelet function is well maintained during storage. This is reflected by the results of immunological and platelet function assays. Rotational thrombelastography (in the case of PRP) and especially resonance thrombography represent promising methods for quality control of platelet concentrates and rapidly provide information about the status of platelet function and the whole clotting process.

Simultaneous measurement of biopolymer-mediated Mac-1 up-regulation and adherence of neutrophils: a novel flow cytometric approach for predicting initial inflammatory interaction with foreign materials

Implantation of any medical device normally causes an inflammatory cell interaction with the foreign material. In vitro cell activation of human neutrophils (Mac-1 upregulation) has been taken as one measure to assess the attributable risk of inflammation due to biopolymers before their clinical application. Mac-1 expression has generally been measured by flow cytometric assays, whereas quantification of neutrophil adhesion to the biopolymer surfaces has been performed by separate and time-consuming assays, e.g. microscopically by differential cell counting. However, due to an increasing number of surface-modified novel biopolymers entering clinical usage, effective testing of their inflammatory potential is now mandatory. To facilitate these analyses, we have developed a novel flow cytometric assay permitting simultaneous measurement of biopolymer-mediated neutrophil activation and adhesion. The biopolymers were used as beads (diameter 25+/-10 microm), and were demonstrated to be non-phagocytosable and non-fluorescent before being co-incubated with whole human blood (range of ratio granulocytes/beads from 5:1 to 1:1). Besides flow cytometric measurement of Mac-1 up-regulated neutrophils as fluorescing events, a fluorescence of the bead population indicates the adherence of activated neutrophils to the biopolymer surface.After establishing this assay, we evaluated it by comparing six different biopolymers. We observed high levels of Mac-1 expression (>70% of positive control) accompanied by increased adhesiveness (>60% of neutrophils) for polyurethane (PUR), polymethylmetacrylate (PMMA), and poly-DL-lactide (PDLLA) beads. Low Mac-1 expression levels (<10%) accompanied by a low percentage of adhering neutrophils (<10%) were observed for polyethylene (PE), polyisoprene (PI), and silicone (SI) beads.

Biocompatibility of a new cell separator studied by flow cytometry: analyses of platelet antigens during apheresis and storage

BACKGROUND

Alterations of platelet antigens are known to occur during cytapheresis and storage. These changes have been shown to be dependent on the biomaterials, techniques, and devices used. In this study, the influence of a new cell separator (AMICUS) and storage container (PL-2410) on platelet glycoproteins was analyzed.

STUDY DESIGN AND METHODS

During plateletpheresis and storage, the levels of platelet glycoproteins and binding of fibrinogen were determined by flow cytometry.

RESULTS

During apheresis, mean channel fluorescence intensity of CD41 a did not change significantly (p = 0.06). A small increase was evident in CD42b mean channel fluorescence intensity, which rose from a baseline level of 178.6 +/- 68.3 to 231.5 +/- 97.9 at the end of the procedure (p<0.05); in CD62p-positive platelets, which increased from 2.0 +/- 0.9 percent to 9.9 +/- 3.9 percent (p<0.05); in CD63-positive platelets, which increased from 1.7 +/- 0.7 percent to 7.9 +/- 2.6 percent (p<0.05); and in the binding of fibrinogen, which increased from 1.9 +/- 0.8 percent positive platelets to 10.5 +/- 2.6 percent (p<0.05). During storage, the mean channel fluorescence intensity of CD41a and CD42b, the percentage of CD62p- and CD63-positive platelets, and the binding of fibrinogen to platelets showed no significant change.

CONCLUSION

These studies show that alterations in platelet antigens and platelet activation occur to a small degree during apheresis and storage. These findings demonstrate generally good biocompatibility of this new cell separator.

Annexin V and platelet antigen expression is not altered during storage of platelet concentrates obtained with the AMICUS cell separator

During storage of platelet concentrate the so-called "storage lesion" occurs. During this time, platelets loose their morphological and functional capacities that are necessary for proper in vivo efficacy following transfusion. Annexin V represents a marker for apoptosis. In this study, Annexin V and additional antigens were analyzed by flow cytometry. Platelet concentrates were obtained with a new cell separator (AMICUS Separator, Fenwal). Following apheresis, platelet units were stored for an experimentally prolonged time of seven days. Daily aliquots of the platelet-rich plasma were obtained to measure Annexin V and platelet antigens CD62p, CD63, CD41a, CD42b, and the binding of fibrinogen. All analyses were performed using flow cytometry. During storage, no significant changes in mean channel fluorescence intensity (MCFI) of CD41a (P = 0.99) and CD42b (P = 0.29), percentage of CD62p+ and CD63+ platelets (P = 0.23 for CD62p; P = 0.52 for CD63), and the binding of fibrinogen to platelets occurred (P = 0.85). Also, the expression of Annexin V remained constant with no significant change (P = 0.36). This study shows that antigens of platelets, obtained with the AMICUS cell separator are well preserved during storage. Regarding Annexin V, no obvious signs of apoptosis can be detected by flow cytometry. These findings demonstrate the high degree of biocompatibility of the apheresis device and storage container.