Cells in Human Blood

To investigate the various cells found within human blood, you can record both the various different cells observed and their abundance. A stained filmof human blood reveals human erythrocytes, lymphocytes, monocytes, platelets, neutrophils, and eosinophils. However, basophils will be difficult to observe. The human erythrocytes are devoid of a nucleus, stained red using Wright's stain method and were fairly smaller compared to the other observed cells. Platelets were seen as small dense particles, with any detail being indistinguishable with the microscope at the highest magnification. Leukocyte size relative to one another is not easily recorded, due to the difficulty of finding cfells adjacent to one another or in the same view. Lymphocytes have a large very dense nucleus, which is surrounded by little transparent cytoplasm. Monocytes also have a large nucleus, surrounded by transparent cytoplasm, more abundant than as seen in the lymphocytes. Neutrophils have large granules of irregular size of stained nuclei, fused together. Eosinophils display greater staining throughout their cytoplasm and have larger granules and more staining in their cytoplasm than neutrophils. Both have their characteristic polymorphic nucleus. The differential leukocyte count was measured by counting the numbers of different leukocytes in numerous different views of the same slide. A percentage value was calculated by divind the total count of a cell type over the total leukocyte count. In order of abundance (%) from most abundant to least, neutrophils, lymphocytes, monocytes, and eosinophils (and basophils at 0%). The values of our leukocyte count were within normal differential range for most leukocytes, however, no basophils were observed due to their rare abundance 0%, reference <1%. Reference: lymphocytes 20-45% range, eosinophils 2-6% range, monocytes 2-6%, neutrophils 40-75%.

All the cellular elements of human blood arise from pluripotent hematopoietic stem cells in the bone marrow. These stem cells divide and differentiate through multiple lineages and result in the diverse array of cells, which include erythrocytes and platelets anbd the leukocytes of the immune system, lymphocytes, monocytes (precursors of macrophages), neutrophils, eosinophils, and basophils. Lymphocytes, which include the B and T cells, bear variable cell-surface receptors for antigen, mediate humoral and cell-mediated immunity respectively and are responsible for the adaptive immune response. Leukocytes that are capable of phagocytosing extracellular pathogens, phagocytes, include the neutrophils and macrophages. Macrophages develop from precursors, monocytes, which circulate in the blood. However, the phagocytes differ in their locations. The neutrophils remain in the blood and circulate throughout the body, until they are recruited to sites of infection while the macrophages reside in tissues. Phagocytes, including the precursor monocytes, constitute the mononuclear-phagocyte system, which is a network that is found in the spleen, lymph nodes, bone marrow, endothelium of capillaries and the lung. Eosinophils are blood-borne cells that are involved in inflammation and in the defense against parasites. Basophils are involved in acute hypersensitivity reactions in which they release their granules, which contain diverse compounds, including histamine. These cells can also be found in sites other than the blood, such as being recruited to sites of inflammation and also most eosinophils are found in the connective tissue immediately underneath respiratory, gut and urogenital epithelium to defend against invading pathogens (1).

The abundance of these leukocytes in the blood varies according to where they reside, their necessity, as well as the amount of self-damage they can cause. Eosinophils and basophils abundance is plit between the blood and tissues and both these leukocytes can cause inflammation and tissue damage in allergic reactions. Hypereosinophilia can cause injury to the endocardium due to circulating eosinophils. Too many eosinophils can pose problem. Eosinophils, and basophils are therefore, normally under tight control to prevent inappropriate toxic responses. Moreover, neutrophils are abundant in the blood but are absent from normal tissues. Both neutrophils and lymphocytes play key roles within the immune system, mainly through circulating in the blood. Neutrophils provide a strong defense against pathogens by preventing their entrance into cells, which could harbor a pathogen hidden from the immune system and preventing their circulation and further spreading the infection throughout the body. Lymphocytes are needed to mediate the adaptive response against an immense array of specific antigens, such as viruses, and to provide lasting immunity to these specific antigens. Lymphocytes increase their numbers when stimulated by antigens. In addition, basophils and eosinophils are found at lower abundances because they can complete their rols in fewer numbers, compared to unique antigen oritented lymphocytes and also neutrophils, that have to phagocytose possibly thousands of pathogens during an infection, a few eosinophils can cause a large amount of inflammation over a large area due to the release of their granules.

References:

1. Janeway, C.A., Travers P., Walport M., and Capra J.D. 1999. Immunobiology: The immune system in health and disease. Garland Publishing, 4th ed., New York, USA, pages 1-40, 2.5-2.22, 3.1-3.12

2. DeFranco, A.I. 1987. Molecular aspects of B-lymphocyte activation. Annu. Rev. Cell Biol. 3:143-178

3. MacLennan, I.C.M. 1994. Germinal centers. Annu. Rev. Immunol. 3:117-139

4. Ravetch, J.V. and Kinet, J. 1993. Fc receptors. Annu. Rev. Immunol. 9:457-492