Ultrastructure of phagocytosis of Salmonella cholerae-suis by pulmonary macrophages in vivo

Abstract

Phagocytosis of virulent Salmonella cholerae-suis in the lungs of pigs was studied by electron microscopy during the period 6 hours-14 days after intranasal infection. All bacteria were phagocytosed by polymorphonuclear leucocytes (PMN) and pulmonary macrophages soon after arrival in distal airways and alveoli. Many organisms were destroyed but some survived and later multiplied within phagocytes. Bacteria were also carried in phagocytic cells to lymphatics and pulmonary capillaries, thereby establishing bacteraemia. Between the 5th and 7th days bacteria caused necrosis of the phagocytes and were released into the tissues in very large numbers. Destruction of all types of lung cell was widespread during this period but the Salmonellae did not penetrate pulmonary cells. From the 9th day onwards bacteria in the lung were restricted to circumscribed abscesses and lymphoid tissue developed throughout the lungs. These latter changes coincided with the appearance of circulating specific antibody.