P-glycoprotein expression in the cells of the immune system during aging

P-glycoprotein (P-gp) is a member of adenosine triphosphate (ATP)-binding cassette transporter superfamily that is expressed in a variety of hematopoietic cells. Although a role of P-gp in multidrug resistance in cancer is well-established, its physiological role in immune cells remains unclear. A role for P-gp in the secretion of cytokines and in cytotoxic effector functions has been suggested; however, knock out experiments suggest that P-gp may not be required for cytokine secretion or effector functions. There is no linear correlation between the expression of P-gp and hyporesponsiveness to antigens in aging. A recently discovered role of P-gp in T-cell survival has been discussed in the context of the aging process. A functional role for P-gp in the context of aging of memory subsets of CD4+ and CD8+ T-cells remains to be investigated. The use of a combination of P-gp expression and efflux of substrate dyes in the presence or absence of modulators of P-gp function to determine the structure-functional relationship and some of the limitations in the use of efflux of fluorescent dyes alone as a measure of the expression of P-gp have been reviewed.