[Pit cells--a tissue form of large granule-containing lymphocytes with natural killer activity]

Basing on structural and functional signs, pit cells and large granule-containing lymphocytes (LGCL) can be considered as the same type of cells. LGCL take origin from bone marrow, circulate in the blood stream and get into tissues as pit cells or as interepitheliocytic lymphocytes. Therefore, on this ground for convenience of studying and understanding these elements of cell immunity a suggestion is made to distinguish the LGCL system, possessing natural killer activity and paracrinic secretion. An increased functional load to the organism results in an intensified getting of LGCL into places of structural reconstructions of tissues (regenerative active zones). The same effector elements--LGCL (pit cells)--in dependence of necessary functional ensuring under various conditions, produce in the surrounding parenchyma both a proliferative effect and its opposite action. The latter can be manifested as a monocellular colliquational necrosis, or as apoptosis. Apoptosis (active cellular death) is of greatest interest. Disturbances of this mechanism can facilitate to an excess proliferation of cells, or to their extreme death; malignant growth and transplant-versus-host reaction can be mentioned as examples, respectively. LGCL play an important role in the immunobiological supervision and are effectors of active ageing mechanisms. Studying of this important link in regulation of quantity of cell population adequate to functional load should help to purposively influence it for stimulating or repressing cell proliferation, depending on certain concrete purposes.