Leukocyte removal

In this chapter we attempt to find a correlation between the chemical nature of the membrane and its suitability to typical clean-up steps such as depyrogenation and leukocyte removal from blood-products. The experimental results of many investigators are compared in this context in regard to the time-average adsorption capacity and the time-average removal factor. The dependence of these two process parameters on the average pore size and the chemistry of the adsorptive membrane are also analyzed. 

Riverbi R, Menini C. Clinical efficacy of five filters specific for leukocyte removal. Vox Sang 1990 ... 

Filtration Filtration (qv) is appHed in blood cell separation to remove leukocytes from ted blood cell (RBC) and platelet concentrates. Centtifugational blood cell separators do not reduce white blood cells (WBC) in red cell and platelet products sufficiently to avoid clinical complications such as GvHD and alloimmunization. A post-apheresis filtration step is needed to further reduce the WBC load. Modem filters are capable of a 3-log reduction in white cell contamination of the blood product, eg, apheresis single-donor platelet units having a typical white cell contamination of 5 x 10 white cells in 4 x 10 platelets can be reduced to a 5 x 10 white cell contamination, a sufficiently low number to avoid severe transfusion reactions. 

The circulatory system carries out many important functions that contribute to homeostasis. It obtains oxygen from the lungs nutrients from the gastrointestinal tract and hormones from the endocrine glands and it delivers these substances to the tissues that need them. Furthermore, it removes metabolic waste products, such as carbon dioxide, lactic acid, and urea, from the tissues. Finally, it contributes to the actions of the immune system by transporting antibodies and leukocytes to areas of infection. Overall, the circulatory system plays a vital role in maintenance of optimal conditions for cell and tissue function. 

Neutrophils are the most abundant of the leukocytes and account for about 60% of the total number of white blood cells. These cells are usually the first to arrive at a site of injury or inflammation. Their primary function is to attack and destroy invading bacteria. In fact, bacterial infection is typically associated with pronounced neutrophilia (an increase in the number of circulating neutrophils). These leukocytes are also involved in removal of tissue debris and therefore play a role in the healing process. 

Pharmacokinetics Well absorbed after both PO and IV administration. Protein binding 8%-24%. Penetrates rapidly and extensively into leukocytes, epithelial cells, and macrophages. Lung concentrations are 2-5 times higher than those of plasma. Elimi-nafed unchanged in fhe urine. Parfially removed by hemodialysis. Half-life 8 hr. 

A calibration curve is recorded for each plate (Fig. 4.1.10). 4-MU standards at absolute concentrations of 0.25 pmol (5 pi), 0.5 pmol (10 pi), 1.0 pmol (20 pi), 2.5 pmol (50 pi) and 5.0 pmol (100 pi) are measured in duplicates. The volume for each well is adjusted with demineralized water to the volume used in the assay. Before measurement, 200 pi stop solution are added and the plate is shaken for 5 min on a plate shaker. Fluorescence is read with an excitation wavelength of 355 nm and an emission wavelength of 460 nm. For leukocyte and dried blood measurements blanks that contain substrate and buffer solution without leukocyte homogenate or dried blood spots are prepared. After incubation and addition of the stop solution, the plate is read immediately for all assays based on leukocytes, while one dried blood spot from an arbitrary sample is added to each blank in case of dried blood assays. Hence, hemoglobin is eluted from blood spots for 30 min and these spots are removed again before measurement. It is crucial to match the age of these specimens to the age of the patient samples. If large variations (several weeks) are evident concerning the age of the samples on the same plate then a separate blank for each patient sample has to be prepared. 

Although the blood is an easily accessible tissue to study, because red blood cells outnumber leukocytes by about 1000 to 1 in the peripheral circulation, the analysis of leukocytes by any technique is difficult unless the red cells can be removed. Techniques for removing red cells usually involve either density gradient centrifugation (pelleting red cells and neutrophils, leaving lymphocytes and monocytes behind to be collected from a layer as a peripheral blood mononuclear cell preparation [PBMC]) or differential lysis of red blood cells, leaving intact the more robust lymphocytes, monocytes, and neutrophils. 

Two major classes of WBCs are involved in removing invading microorganisms by a process of phagocytosis. These are polymorphonuclear leukocytes and mononuclear phagocytes, or monocytes. In tissues, monocytes differentiate into macrophages and, in the brain, into microglia... 

Acute intravasation of barium sulfate into the circulatory system of an adult female patient following a barium enema procedure caused the compound to be deposited in blood vessels throughout the body, including the lungs, and resulted in respiratoryfailure (Cove and Snyder 1974). Acute parenteral administration of barium compounds to animals has been shown to result in paralysis of the respiratory muscles (Roza and Berman 1971). Similar respiratory paralysis is frequently encountered in cases of acute exposure in humans and animals by ingestion or inhalation. Intratracheal administration of barium sulfate into rat lungs produced a mild inflammatory reaction (Huston et al. 1952). Barium sulfate could not be removed by either polymorphonuclear leukocytes or monocytes. A tissue reaction followed however, no fibrosis was observed. Since this mode of entry is similar to inhalation, these results may be significant for cases of inhalation exposure. 

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