Regional and systemic immune responses in a murine model of empyema

The extent to which circulating leukocytes reflect functional capacity at the site of infection is unclear despite a century of debate. We conducted experiments designed to clarify those relationships as well as the relationship of pleural and peritoneal responses to infection. Empyema was established in inbred CBA/J mice by introducing Escherichia coli and Bacteroides fragilis into the thoracic cavity through a limited thoracotomy. Walled off abscesses appeared seven days after the introduction of infection. Cell surface expression of murine class II major histocompatibility antigen was measured in peripheral leukocytes, thoracic and peritoneal cavity exudate leukocytes and abscess cells for 60 days after the introduction of infection. The peripheral antibody response was determined by measuring immunoglobulin M (IgM) and immunoglobulin G (IgG) specific for the two organisms. The results demonstrated that, after introduction of infection into the thoracic cavity, mice mounted a specific systemic humoral immune response by producing IgM and IgG. There was a pronounced concomitant cellular response in thoracic and peritoneal cavity exudate cells. However, there was no evidence of a systemic cellular response in circulating lymphocytes or monocytes and polymorphonuclear leukocytes measured as a single group. We conclude from these experiments that measurements of peripheral immune parameters may adequately reveal the humoral response to infection, but it does not reflect the local immune cellular response. Furthermore, a special relationship exists between the peritoneal and the thoracic cavities, whereby an inflammatory process in the thoracic cavity leads to a marked activation of inflammatory process in the peritoneal cavity without affecting peripheral circulating cells to the same extent.