Immunohistological characterization of leukocytes in the lungs of healthy mice and after bacterial intratracheal infection

Leukocytes in the peripheral lung parenchyma of mice have not been characte rized histologically during bacterial infection. The aim of this study was to investigate (a) the immunohistological characteristics of healthy murine lungs and (b) the cell kinetics during acute inflammation. BALB/c and MF1 mice were examined; as well as transgenic mice with the gene defect of cyst ic fibrosis (CP) in the airways as an animal model for this disease. MF1 mi ce served as controls for the transgenic animals. Lavaged and perfused lung s were snap frozen. B and T lymphocytes, CD4+ and CD8+ cells, dendritic cel ls, neutrophils and a subset of macrophages were enumerated on cryostat lun g sections. The lung tissue and bronchoalveolar lavage (BAL) of BALB/c mice , infected intratracheally with Haemophilus influenzae type b (Hib), were s tudied at different time points after infection. In the lungs of healthy mi ce, including CF mice, the largest population was that of T cells, CD4+ cel ls being always more frequent than CD8+ cells. During acute inflammation th e number of neutrophils in the lung parenchyma and BAL increased strongly w ithin the first hours after bacterial instillation and reached baseline lev els within one week. This study provides a semi-quantitative analysis of im munocompetent cells in normal and infected murine lung tissue. Differences in cell numbers are found between different strains. Moreover, the cellular reaction during Hib infection in mouse lungs is dominated by neutrophils, as expected in a primary immune response. In uninfected CF mice the numbers and distribution of immune cells in the lung tissue are normal, indicating that the cellular defense is adequate.