Activity of macrophage and neutrophil cellular fractions from normal and immune sheep against Listeria monocytogenes.

Cellular immunity to Listeria monocytogenes infection was studied by assaying for antibacterial activity in fractions of leukocytes collected from the peritoneal cavity, lungs, and mammary glands of immunized sheep. The cells were collected in populations that were largely either macrophages or neutrophils. Mechanically disrupted cells were divided into nuclear, lysosomal, and supernatant fluid fractions and then subjected to freezing and thawing. Comparison with similarly treated rabbit cells showed that greater fragility exists in the lysosomes of sheep cells, as indicated by the amount of acid phosphatase activity released. Inhibition of bacterial growth was assayed in a broth medium at pH 4.6. As expected, nuclear and lysosomal fractions from neutrophils were inhibitory. Some antibacterial activity was found in nuclear fractions of macrophages. The lysosomes of macrophages collected from the peritoneal cavity and the mammary gland did not inhibit the growth of L. monocytogenes. Peritoneal macrophages were allowed to interact with sensitized lymphocytes and an avirulent strain of L. monocytogenes for 4 hr prior to disruption and fractionation, but antibacterial activity was not detected. Pulmonary alveolar macrophages from 5 out of 16 sheep contained Listeria inhibitory activity in their lysosomes. The mechanism was inhibitory but not bactericidal.