Purpose: Phagocytosis is a major mechanism of defense against bacterial infections. The ingestion of bacteria by phagocytes involves a variety of cell membrane recognition structures and, among them, immunoglobulin receptors. The aim of this study was to test the phagocytic activity of granulocytes and monocytes of intensive care unit (ICU) patients, and to evaluate the effects of intravenous polyvalent immunoglobulins (IVIG) used as adjunct treatment of nosocomial pneumonia on some phagocyte membrane receptors of these patients.
Materials and methods: The phagocytic activity of granulocytes and monocytes of 41 mechanically ventilated patients with nosocomial bacterial pneumonia was studied during the acute phase of infection. These ICU patients were compared with 21 hospitalized, noninfected volunteer patients hospitalized in a medical ward. Peripheral blood granulocytes and monocytes were studied. Of the 41 ICU patients, after randomization, 21 received IVIG at a dose of 1 g/kg for 3 days. The 41 ICU patients were compared with the 21 non-ICU, noninfected hospitalized controls. The 21 ICU patients who received 3 days of IVIG were also compared with the 20 ICU patients not receiving IVIG. Cells were tested in standard immunoglobulin-free medium (fetal calf serum) and in the presence of patients' serum. Blood granulocytes and monocytes were purified and separately exposed to three types of particles: antibody-coated erythrocytes (to test immunoglobulin receptors), opsonized zymosan (to test C3 receptors), and glutaraldehyde-treated erythrocytes (to test lectinlike or other nonspecific binding sites). Phagocytosis and superoxide anion production (oxidative burst) were measured.
Results: Granulocytes of ICU patients compared with those of non-ICU, noninfected patients exhibited a substantial decrease of zymosan ingestion (P < .05), whereas phagocytosis of other particles was normal. Monocytes from the ICU patients, compared with those of the non-ICU, noninfected patients, displayed an unselective overall decrease of phagocytic ability for the three particle types (P < .05). The phagocytosis activity of the three membrane receptor species of blood monocytes and granulocytes of ICU patients was not significantly modified by the IVIG infusion. For both monocytes and granulocytes, no significant improvement was observed in the fraction of cells that ingested at least one foreign particle and the mean number of particles per cell having phagocytized at least one foreign particle. Granulocyte and monocyte functions were also tested by the production of reduced ferricytochrome and no significant improvement in the oxidative burst was observed after infusion of IVIG.
Conclusion: Infected ICU patients display a deficiency of phagocytosis membrane receptors of blood granulocytes and monocytes. The addition of IVIG to standard therapy does not improve the phagocytic activity of ICU patients with nosocomial pneumonia.