Two distinct receptors mediate nonopsonic phagocytosis of different strains of Pseudomonas aeruginosa

Complement receptor 3 (CR3) mediates both opsonic and nonopsonic phagocytos is of bacteria. Leukocyte adhesion deficiency (LAD) allows for the study of CR3-dependent phagocyte-bacterial ingestion, since LAD phagocytes do not e xpress this receptor. Phagocytes from an infant with LAD were unable to ing est 50% of the Pseudomonas aeruginosa strains studied, which indicates a re quirement for CR3. However, the remaining strains were phagocytosed in the absence of CR3, and ingestion was blocked by monoclonal antibodies directed at CD14. This CR3/CD14 receptor bias was further confirmed by using thiogl ycollate-elicited murine peritoneal macrophages, which have nonfunctional C R3 before activation. Results indicate that either CR3 or CD14 is involved independently in nonopsonic phagocytosis of different P. aeruginosa strains . Clearance of P. aeruginosa from the endobronchial space may be facilitate d by nonopsonic phagocytosis, since low levels of opsonins are present. The impact of lung infection with P. aeruginosa may be determined, in part, by the phagocytic receptor that mediates ingestion.