Oleic acid increases cell surface expression and activity of CD11b on human neutrophils

Traumatic bone injury frequently results in the release of marrow-derived fatty material into the circulation. This may lead to the syndrome of fat embolism, associated with the generation of free fatty acids, the sequestration of neutrophils in the lungs, and the subsequent development of acute respiratory distress. Neutrophil accumulation in tissues requires their adherence to vascular endothelial cells and involves the beta2 integrin, CD11b/CD18 (Mac-1). We now report that the exposure of isolated human neutrophils to oleic acid causes a rapid increase in the cell surface expression and affinity state of CD11b, particularly under acidic conditions that are typical of inflammatory sites. Oleic acid also triggers neutrophil aggregation and neutrophil adherence to both fibrinogen-coated surfaces and confluent cultures of HUVEC. These processes are blocked by CD11b-specific inhibitors, including neutrophil-inhibitory factor and mAbs to CD11b. These observations may help explain the etiology of so-called fat embolism wherein trauma-induced release of fatty material causes pulmonary neutrophil accumulation and the development of acute respiratory distress.