User:Bike2022/Null cell

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A null cell, or more commonly used, natural killer cells, are a large granular lymphocyte that develops inside the bone marrow and attacks pathogens and abnormal cells. The term null cell is old and has been taken over by the term natural killer cells or killer cells. There are common characteristics that null cells lack to be categorized into surface markers in mature B-cells and T-cells. Null cells are in fact T cells that fail to express CD2 (Licence et al., 1995). Even though they are large granular lymphocytes, they are still relatively small, chromophobic cells. When the term chromophobic is used, it means when viewed under a light microscope, these cells appear to be small. Null cells are present in small numbers in lymphoid organs but are often found in nonlymphoid tissues (Pabst and Binns, 1989; Barman et al., 1996). While they do not contain known anterior pituitary hormones in their cytoplasm, they do contain secretory granules that may contain various properties like; hormone pieces, forerunners, or biologically inactive substances. The cells are seen as a representation of resting cells, precursors of various cell types, or an unknown cell type.

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Null cells account for a small proportion of the lymphocytes found in an organism. As mentioned before, they are quick to act in the presence of pathogens like viruses and attack viral-infected or tumor cells, more specifically non-MHC-restricted manner. In subpopulations of mononuclear cells in aging humans, the number of null cells has increased over time. Recently, using developed monoclonal antibodies against natural killer cells combined with T-Cell markers in two-wavelength immunofluorescence, 13 subpopulations of mononuclear cells were defined and compared in two groupings of individuals. What was found was that in the elderly (75-84) age group was an increase in the null cell population because of an increase in natural killer cells. More specifically, the CD16+ and Leu7+ subsets of natural killer cells. Additionally, CD8+ suppressor and cytotoxic cells were found to be decreased. Changes are believed to be due to defects involved with an aging immune system and can be used as a representation of a healthy immune system in the healthy aged group and can be linked to survival. The values that were uncovered can be implemented in monitoring efforts to rebuild defective immune systems due to aging. Null cells have also been found in some cancers. In the pituitary gland, null cell adenomas have been found. Null cells have also been identified in the nontumorous adenohypophysis, suggesting that null cell adenomas are derived from preexisting non-neoplastic null cells. That being said, when it comes to non-functioning tumors and adenomas, null cells comprise around 20% of them.

Interestingly, in animals like newborn cats, lymphocytes will mature both phenotypically and functionally for a time after birth. Null lymphocytes will have a steady decrease with a linked increase in T and B lymphocytes from 56 days of gestation through to 8 weeks old (Sellon et al., 1996). When using a cell line that is made by cloning an original white blood cell (monoclonal antibodies) there is evidence for recirculation of lymphocytes, particularly in null-cell subsets which are found from the bronchoalveolar spaces back into regional draining lymph nodes (Pabst and Binns, 1995).