Differential expression of function-related antigens on blood monocytes in children with hemolytic uremic syndrome

Monocytes (Mo) mediate central func- tions in inflammation and immunity. Different sub- populations of Mo with distinct phenotype and functional properties have been described. Here, we investigate the phenotype and function of pe- ripheral Mo from children with hemolytic uremic syndrome (HUS). For this purpose, blood samples from patients in the acute period of HUS (HUS AP) were obtained on admission before dialysis and/or transfusion. The Mo phenotypic characterization was performed on whole blood by flow cytometry, and markers associated to biological functions were selected: CD14 accounting for lipopolysac- charide (LPS) responsiveness, CD11b for adhe- sion, Fc receptor for immunoglobulin G type I (FcRI)/CD64 for phagocytosis and cytotoxicity, and human leukocyte antigen (HLA)-DR for anti- gen presentation. Some of these functions were also determined. Moreover, the percentage of CD14 CD16 Mo was evaluated. We found that the entire HUS AP Mo population exhibited re- duced CD14, CD64, and CD11b expression and decreased LPS-induced tumor necrosis factor pro- duction and Fc-dependent cytotoxicity. HUS AP showed an increased percentage of CD14 CD16 Mo with higher CD16 and lower CD14 levels compared with the same subset from healthy children. Moreover, the CD14 CD16- Mo sub- population of HUS AP had a decreased HLA-DR expression, which correlated with severity. In con- clusion, the Mo population from HUS AP patients presents phenotypic and functional alterations. The contribution to the pathogenesis and the pos- sible scenarios that led to these changes are discussed. J. Leukoc. Biol. 78: 853-861; 2005.