Phenotypic characterization of alveolar monocyte recruitment in acute respiratory distress syndrome

In 49 acute respiratory distress syndrome (ARDS) patients, the phenotype of alveolar macrophages (AMs) was analyzed by flow cytometry. Bronchoalveolar lavage (BAL) was performed within 24 h after intubation and on days 3-5, 9 -12, and 18-21 of mechanical ventilation. The 27E10(high)/CD11b(high)/ CD71 (low)/25F9(low)/HLADR(low)/RM3/1(low) AM population in the first BAL indica ted extensive monocyte influx into the alveolar compartment. There was no e vidence of increased local AM proliferation as assessed by nuclear Ki67 sta ining. Sequential BAL revealed two distinct patient groups. In one, a decre ase in 27E10 and CD11b and an increase in CD71, 25F9, HLA DR, and RM3/1 sug gested a reduction in monocyte influx and maturation of recruited cells int o AMs, whereas the second group displayed sustained monocyte recruitment. I n the first BAL from all patients, monocyte chemoattractant protein (MCP)-1 was increased, and AMs displayed elevated MCP-1 gene expression. In sequen tial BALs, a decrease in MCP-1 coincided with the disappearance of monocyte -like AMs, whereas persistent upregulation of MCP-1 paralleled ongoing mono cyte influx. A highly significant correlation between BAL fluid MCP-1 conce ntration, the predominance of monocyte-like AMs, and the severity of respir atory failure was noted.