Expansion of monocyte-like cells expressing natural killer cell-associated antigens in response to low-dose total lymphoid irradiation

We have previously shown that total lymphoid irradiation conditioning of baboons before renal transplantation is a potent immunosuppressive strategy, resulting in quiescent T cell function and increased NK cell activity. This paper shows that proportion of cells expressing NK- associated antigens, which expand during and after total lymphoid irradiation, includes large, granular cells expressing surface antigens associated with monocytes. NK cells and monocytes from peripheral blood were detected and quantified using an array of fluorescent-labelled monoclonal antibodies and flow cytometry. During and after exposure to total lymphoid irradiation there was an increase in the frequency of large, granular CD11b(+) and CD16(+), CD56(+), CD16(+) CD38(+) cells and absolute numbers of CD14(+)CD11b(+) and CD14(+) CD16(+) mononuclear cells. This suggested that expansion of a unique population of CD14(+) monocytes, co-expressing CD16 and CD11b antigens, normally found on NK cells. Consequently, the significant increase in CD14(+) CD16(+) cells demonstrates that CD16(+) cells do not solely define NK cells in the mononuclear cell fraction isolated during and after this form of radioconditioning.