Separation of leukocytes from blood and bone marrow

Blood is a specialized body fluid composed of four main components: plasma, white blood cells (leukocytes), red blood cells (erythrocytes), and platelets (thrombocytes). Unlike red blood cells and platelets, all white blood cells are nucleated and can be classified by their nuclei structure as mononuclear or polymorphonuclear cells. White blood cells have an important role in immunity to protect the body against both infectious disease and foreign invaders cementing their utility for immunological studies. Thus, isolation of mononuclear and polymorphonuclear cells from blood serves as the starting point for a wide spectrum of immunology studies. Lymphocytes and monocytes are the two main categories of mononuclear white blood cells with one-lobed nucleus in the immune system with specific and important roles in defending the body from infection, cancer, and other foreign invaders. Lymphocytes include natural killer (NK) cells, T (thymus) cells, and B (bone marrow- or bursa-derived) cells and are the main type of cell found in lymphatic system. In humans, lymphocytes make up the majority of the peripheral blood mononuclear cell (PBMC) population (comprising 70-90% of the PBMC population), followed by monocytes (10-30% of PBMC population), and a small percentage of dendritic cells (1-2% of PBMC population). PBMCs are important for immunological studies and clinical applications such as diagnostics and disease treatment. Some key applications of PBMCs include immune response assessment, biomarker identification, vaccine development and cancer immunotherapy. Early methods for isolating leukocytes involved mixing blood with a compound which aggregated the erythrocytes and to a much lesser extent, the leukocytes. With centrifugation, these aggregated erythrocytes pelleted due to their increase density, while the leukocytes remained in solution. However, the recovery of leukocytes was less than desired because the cells can be trapped by and sedimented with the aggregated erythrocytes. In 1968, BØyum1 introduced a more convenient and rapid separation using centrifugation through a Ficoll-sodium metrizoate solution. This separation method takes advantage of cell density differences of the components in whole blood that, when centrifuged in the presence of a density gradient media, exhibits a unique migration pattern through the medium allowing distinct cell populations to be fractionated. Distinguished from mononuclear leukocytes, polymorphonuclear leukocytes have the varying shapes of the nucleus, which is usually lobed into three segments. They are responsible for combating bacterial and fungal infections. Neutrophils are the most abundant polymorphonuclear leukocytes, and the other types (eosinophils, basophils, and mast cells) have much lower populations. A pain point for many researchers is how to specifically isolate mononuclear and polymorphonuclear cells from blood with high yield and cell viability. MP Biomedicals offers three products for the isolation of mononuclear and polymorphonuclear cells from human peripheral blood as well as bone marrow, and umbilical cord blood. The lymphocyte separation medium (LSM™), LymphoSep®, and Mono-Poly® Resolving Medium have been used for many applications by researchers worldwide.