The article discusses the mechanisms of acquired resistance to Listeria monocytogenes in mice. It highlights that while antibodies can influence bacterial fate through lysis or opsonisation, some organisms can multiply within cells, leading to a discrepancy between antibody response and resistance. The study focuses on the role of cellular immunity in resistance, particularly in mice, which develop true acquired resistance to Listeria. The research involved studying the pathogenesis of listeriosis in mice, examining the growth cycle of Listeria in vivo, and analyzing the immunological response to the bacteria. The study found that Listeria monocytogenes can survive and multiply within macrophages, leading to the formation of plaques. The virulence of the bacteria was enhanced through mouse passage and adaptation to macrophage cultures. The results showed that the derived strains were more virulent and efficient at forming plaques compared to the wild strain. The survival rates of the wild and derived strains in the spleen and liver were compared, with the derived strains showing better survival within cells. The growth cycle of Listeria in vivo was analyzed, showing that the bacteria initially multiply in the spleen and liver, then inactivate. The study also examined the delayed-type hypersensitivity response in mice, finding that the antibacterial response and hypersensitivity were essentially coincident events. The study further demonstrated that macrophages from immune mice could inactivate ingested Listeria, indicating that the host's mononuclear phagocytes play a role in acquired resistance. The research concluded that the resistance to Listeria monocytogenes in mice is primarily due to the host's macrophages, which can inactivate the bacteria. The study also showed that the antibacterial mechanism is closely linked to the development of Listeria-resistant properties in host macrophages. The findings suggest that the resistance is not solely due to humoral factors but is instead mediated by cellular mechanisms. The study highlights the importance of macrophage activity in the host's defense against Listeria monocytogenes.The article discusses the mechanisms of acquired resistance to Listeria monocytogenes in mice. It highlights that while antibodies can influence bacterial fate through lysis or opsonisation, some organisms can multiply within cells, leading to a discrepancy between antibody response and resistance. The study focuses on the role of cellular immunity in resistance, particularly in mice, which develop true acquired resistance to Listeria. The research involved studying the pathogenesis of listeriosis in mice, examining the growth cycle of Listeria in vivo, and analyzing the immunological response to the bacteria. The study found that Listeria monocytogenes can survive and multiply within macrophages, leading to the formation of plaques. The virulence of the bacteria was enhanced through mouse passage and adaptation to macrophage cultures. The results showed that the derived strains were more virulent and efficient at forming plaques compared to the wild strain. The survival rates of the wild and derived strains in the spleen and liver were compared, with the derived strains showing better survival within cells. The growth cycle of Listeria in vivo was analyzed, showing that the bacteria initially multiply in the spleen and liver, then inactivate. The study also examined the delayed-type hypersensitivity response in mice, finding that the antibacterial response and hypersensitivity were essentially coincident events. The study further demonstrated that macrophages from immune mice could inactivate ingested Listeria, indicating that the host's mononuclear phagocytes play a role in acquired resistance. The research concluded that the resistance to Listeria monocytogenes in mice is primarily due to the host's macrophages, which can inactivate the bacteria. The study also showed that the antibacterial mechanism is closely linked to the development of Listeria-resistant properties in host macrophages. The findings suggest that the resistance is not solely due to humoral factors but is instead mediated by cellular mechanisms. The study highlights the importance of macrophage activity in the host's defense against Listeria monocytogenes.