EXPANDED CD14(+) CD16(+) MONOCYTE SUBPOPULATION IN PATIENTS WITH ACUTE AND CHRONIC INFECTIONS UNDERGOING HEMODIALYSIS

Infections are frequent complications in end-stage renal failure patie nts undergoing hemodialysis (HD), and peripheral blood monocytes are i mportant cells in host defense against infections. The majority of cir culating monocytes express high levels of lipopolysaccharide receptor antigen CD14 and are negative for the immuno-globulin Fc gamma recepto r type m (CD16). We studied the occurrence of a minor subpopulation co expressing low levels of CD14 together with CD16 in HD patients. In he althy controls CD14(+) CD16(+) monocytes account for 8% +/- 4% of CD14 (+) monocytes, with an absolute number of 29 +/- 14 cells/mu l. In sta ble HD patients the CD14(+) CD16(+) subpopulation was significantly el evated (14% +/- 3%, or 66 +/- 28 cells/mu l), while the number of CD14 (++) monocytes (monocytes strongly positive for CD14) remained constan t. In HD patients suffering from chronic infections a further rise in CD14(+) CD16(+) monocytes was observed (128 +/- 71 cells/mu l; P < 0.0 1) such that this subpopulation constituted 24% of all blood monocytes . In contrast, numbers of CD14(++) cells did not change compared to th ose for stable HD patients, indicating that the CD14(+) CD16(+) monocy te subpopulation was selectively expanded. During acute infections the CD14(+) CD16(+) cell subpopulation always expanded. A whole-blood ass ay revealed that CD14(+) CD16(+) monocytes exhibited a higher phagocyt osis rate for Escherichia coil bacteria than CD14(++) monocytes, under lining their role during host defense. In addition, CD14(+) CD16(+) mo nocytes expressed higher levels of major histocompatibility complex (M HC) class II antigens (HLA-DR, -DP, and -DQ) and equal amounts of MHC class I antigens (HLA-ABC). Thus, CD14(+) CD16(+) cells constitute a p otent phagocytosing and antigen-presenting monocyte subpopulation, whi ch is expanded during acute and chronic infections commonly observed i n chronic HD patients.