MODULE SUPPLEMENT: IMMUNE SYSTEM
The "Natural Killer" and the "LAK"

Two other cells that are generally considered part of the non-specific defense system warrant mention. The first is the Natural Killer Cell. These are large granular lymphocytes (WBC's) with unique membrane markers.

Of note is that changes that occur with age differ depending on whether animals or humans are studied. In a recent (1999) article, Pawelec and his colleagues suggest that there is general consensus that there is an increase in absolute and relative numbers of Natural Killer Cells that seems related to an expansion in the mature subset. They also support the controversial findings about the functional capacity of these cells. Mouse studies show a profound loss of spleen and lymph node derived NK function, but when blood samples are used in human studies, such loss of function is not observed. Generally, it appears that there is a subtle age associated deficit in NK function that may then affect other cellular functioning including that of the macrophage.

Thus while more data are certainly needed, it may be that NK activity in the central immune compartments is age sensitive which would increase an older adult's vulnerability to neoplastic or viral illnesses.

Closely related to the NK cell is the Lymphokine Activated Killer Cell (LAK). These are morphologically like NK cells but are able to kill a broader spectrum of fresh tumor cells. There seems to be agreement that LAK function declines with age, but like NK cells, the decline may be subtle and more data are needed.