Null cell

A null cell is a large granular lymphocyte that develops inside the bone marrow.[1] Null cells lack the common characteristic surface markers that can be found in mature B-cells and T-cells.[1] They are rapidly stimulated in the presence of pathogens like viruses and attack viral-infected or tumor cells in a non MHC-restricted manner.[1] Null cells make up a small proportion of the lymphocytes that can be found in an organism. The term null cell is no longer commonly used; they are normally referred to as natural killer (NK) cells or killer cells.[1]

In subpopulations of mononuclear cells in aging human, the number of null cells has been shown to increase 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+ subset 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.[2]

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 nontumorous adeno-hypophysis. This suggests that null cell adenomas are derived from preexisting non-neoplastic null cells.[3]

References
  1. null cell. (n.d.) Mosby's Medical Dictionary, 8th edition. (2009). Retrieved November 29, 2015 from http://medical-dictionary.thefreedictionary.com/null+cell
  2. Ligthart, G J; van Vlokhoven, P C; Schuit, H R; Hijmans, W (November 1986). "The expanded null cell compartment in ageing: increase in the number of natural killer cells and changes in T-cell and NK-cell subsets in human blood". Immunology. 59 (3): 353–357. ISSN 0019-2805. PMC 1453188. PMID 2947844.
  3. Kovacs, Kalman; Horvath, Eva; Ryan, Nancy; Ezrin, Calvin (1980-06-01). "Null cell adenoma of the human pituitary". Virchows Archiv A. 387 (2): 165–174. doi:10.1007/BF00430697. ISSN 1432-2307.


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