Phagocytosis. Clinical disorders of recognition and ingestion

Tentative conclusions concerning the role of recognition and ingestion of microorganisms by phagocytes in host defense and the consequences of disorders of phagocytosis can be derived by correlating a) knowledge about recognition and ingestion derived from studies in vitro, b) investigations of the clearance of particulate matter from the circulation of animals and man, and c) analyses of the behavior of phagocytes in patients susceptible to recurrent pyogenic infections. Deficiency of the major serum recognition-conferring (immunoglobulins and complement proteins that deposit a fragment of C3 on microbes) prevents the optimal clearance of virulent encapsulated pathogens by fixed mononuclear phagocytes. Confrontation of phagocytes with particulate matter appearing in pathologic states (viruses, immune complexes, damaged erythrocytes in sickle cell anemia and other hemoglobinopathies) diverts them from their normal task of clearing opsonized encapsulated microorganisms. Corticosteroids impair the phagocytic capacity by an unknown mechanism. Major impediments to progress in this field are inadequate assays for phagocytosis and the difficulty in measuring phagocytosis in the intact organism.