IMPAIRED PHAGOCYTE RESPONSES TO LIPOPOLYSACCHARIDE IN PAROXYSMAL-NOCTURNAL HEMOGLOBINURIA

Bone marrow-derived cells from patients suffering from paroxysmal noct urnal hemoglobinuria (PNH) show a defect in the expression of phosphat idylinositol-anchored membrane proteins, including the CD14 molecule. Blocking experiments with anti-CD14 monoclonal antibodies have shown t hat lipopolysaccharide (LPS)-induced tumor necrosis factor alpha produ ction by monocytes depends on the interaction between CD14 and a compl ex formed by LPS and LPS-binding protein. We used a whole-blood model to examine the LPS-induced production of tumor necrosis factor alpha a nd interleukin-6 in PNH patients and healthy volunteers. At low endoto xin concentrations (1 ng/ml), PNH patients displayed a marked defect i n the production of both cytokines, whereas at high LPS concentrations (100 ng/ml), cytokine production was similar to that in healthy volun teers. Using flow cytometry, we also studied the expression of the adh esion molecules Mac-1 (CD11b/CD18) and ICAM-1 (CD54) by monocytes and granulocytes after LPS stimulation. Compared with phagocytes from heal thy volunteers, CD14-deficient cells showed poor Mac-1 and ICAM-1 upre gulation when whole blood was stimulated with LPS (1 ng/ml), whereas t heir response to higher LPS doses (100 and 1,000 ng/ml) was essentiall y normal. The importance of the CD14 molecule in the activation of pha gocytes by low LPS concentrations was confirmed by the inhibitory effe ct of an anti-CD14 antibody both in healthy volunteers and in PNH pati ents. Since these patients produce the soluble form of the CD14 molecu le, these data suggest that soluble CD14 could play a role in phagocyt e responses to LPS. We conclude that, in whole blood, phagocytes from PNH patients show impaired responsiveness to LPS and this phenomenon i s most probably related to their defect in expression of membrane CD14 .