Leukocyte depletion: a biotechnical transfusion story

Leukocyte depletion for safe blood transfusion

Leukocytes have ability to distinguish between self cells (body own cells) and foreign (allogenic) cells on the basis of human leukocyte antigen (HLA) proteins that are present on the cell membrane and are effectively unique to a person. During allogenic blood transfusion a person receives large number of allogenic donor leukocytes and these are recognized as foreign cells by the recipient immune system which leads to several adverse reactions. To avoid such leukocyte-mediated adverse reactions leukodepleted blood transfusion is required. Leukocytes can be separated on the basis of size, dielectric properties, by affinity separation, freeze-thawing and centrifugation but all these methods are time consuming and costly. Filtration is another method for leukocyte depletion that is comparatively less expensive and more efficient as it gives more than 90% leukodepletion of blood along with minimal cell loss. However, present filtration procedures also have some limitations as they work efficiently with blood components but not with whole blood and show non-specific adhesion of large number of platelets and red blood cells along with leukocytes. All the currently available filters are costly, which has been a major reason for their limited application. Therefore, demand for a more efficient and cost-effective filter is high in medical community and scientists are attenpting to improve the efficiency of currently available filters. The present review gives an overview of the significance of leukodepleted blood transfusion and focuses on different methods for leukocyte depletion and challenges involved in all these technologies.

An in vitro system for testing leucocyte and leukaemic cell line adhesion to synthetic fibres

Leucocyte adhesion is an important phenomenon in antimicrobial defence, inflammation and immunological mechanisms and has been shown to be dependent upon specialized adhesion molecules. To prevent side-effects related to blood transfusion (e.g. anti-human leucocyte antigen immunization and transmission of infectious agents) leucocyte reduction of blood products is now systematically performed in various countries. The most common system used for leucoreduction is blood filtration. For further understanding of the mechanisms responsible for the interaction between leucocytes and the fibres present in filters we used a flow chamber to study the adhesion of leucocytes and leukaemic cell lines to different types of fibre. Adhesion was quantified using video-microscopy and computer image analysis. Our results demonstrate that adhesion to filter fibres was dependent on the expression of beta2-integrins CD11--CD18 and was inhibited by anti-CD18. The amount of fibres present, their spatial arrangement and the physicochemical characteristics of the fibres were important factors in leucocyte adhesion. Leucocyte adhesion was the highest to polyethylene terephthalate (PET) and polyimide fibres. Lymphocytes or lymphocytic cell lines were poorly adherent to PET fibres. The retaining capacity of leucocyte filters can be improved by taking into account the different parameters for the design of new filters

Human promyelocytic cell line: a convenient tool for studying the molecular basis of WBC filtration

BACKGROUND

Blood filtration is a technique widely used to reduce the levels of WBCs in blood components. Several studies have been conducted to define the factors that are involved in WBC reduction, but the various mechanisms are not clearly delineated. This study explored the role of WBC adhesion molecules in WBC reduction during filtration.

STUDY DESIGN AND METHODS

A minifilter has been developed that has properties similar to those of the standard filter (Sepacell, Asahi Medical) but that allows a smaller volume of blood to be used (15 mL). WBC reduction was achieved to a similar extent in the standard filter and the minifilter (4.15 log and 4.18 log, respectively). Samples of human promyelocytic cell line (HL60) were filtered before and after differentiation induced by vitamin D3 (D3-HL60). Flow cytometry was used to characterize the D3-HL60 filtrates and to count the WBCs after filtration.

RESULTS

HL60 was retained in the filter to the same extent as all other WBCs. A higher level of integrin receptors (CD11b/CD18; CD11c/CD18) was expressed by D3-HL60 than by HL60. When the blood was incubated with anti-CD11b, anti-CD11c, or anti-CD18, fewer D3-HL60 cells were trapped by the filter, while only anti-CD11b alters HL60 retention in the filter.

CONCLUSION

The receptors CD11b/CD18 and CD11c/CD18 appear to bind to the filter fibers and to be one of the mechanisms responsible for WBC retention.