['Cardiopulmonary bypass (CPB) is associated with a disturbed immune response, e.g., impaired HLA-DR expression on monocytes and the release of pro- and anti-inflammatory cytokines. Cytokine release plays a role in the pathogenesis of postoperative systemic inflammatory response syndrome (SIRS) and immune system deterioration, e.g., impaired monocyte and polymorphonuclear neutrophil (PMN) function, factors that ultimately lead to an increased susceptibility to infections. To gain a further understanding, we investigated HLA-DR expression on monocytes and on B- and T-lymphocytes. In addition, we investigated the IN VITRO effect of the immunostimulating hematopoietic growth factor granulocyte-macrophage colony-stimulating factor (GM-CSF) on HLA-DR expression of these cell types. Neither HLA-DR expression on B- and T-lymphocytes nor the effects of GM-CSF in cardiac surgical patients have been studied before.', 'In 16 patients undergoing elective cardiac surgery with CPB, counts of circulating leukocyte subsets as well as HLA-DR expression on monocytes, B- and T-lymphocytes were measured by flow cytometry before, immediately after CPB, and on the 2nd and 10th postoperative days. Treatment with GM-CSF was performed IN VITRO in whole blood cultures with 100 ng/ml recombinant human GM-CSF for 20 h.', 'Monocyte HLA-DR expression was attenuated immediately after CPB (125 +/- 4 mean channel fluorescence [MCF] vs. 143 +/- 2 MCF preoperatively, mean +/- SEM, P < 0.001). HLA-DR expression further decreased on the 2nd day after CPB and did not normalize until the 10th day after the operation. In contrast, HLA-DR expression on T-cells was unchanged, whereas HLA-DR expression on B-cells did not decrease before the 2nd day after CPB (152 +/- 3 MCF vs. 170 +/- 2 MCF preoperatively, P < 0.001). IN VITRO GM-CSF treatment increased HLA-DR expression on monocytes prepared after CPB to a degree comparable to preoperative values. HLA-DR expression on B-lymphocytes could not be restored by GM-CSF.'] Does granulocyte-macrophage colony-stimulating factor ( GM-CSF ) restore decreased monocyte HLA-DR expression after cardiopulmonary bypass?