Decreased pulmonary alveolar macrophage bactericidal activity in splenectomized rats

The organism most frequently encountered in postsplenectomy sepsis is Streptococcus pneumoniae, which is thought to invade via the upper respiratory tract. This study assesses the phagocytic and bactericidal activity of pulmonary alveolar macrophages (PAM) in normal, splenectomized, and one-third splenectomized autotransplanted rats at 8 weeks of age, 7 weeks post surgery. The PAMs from both the splenectomized and control rats all expressed the same ability to phagocytose latex beads and Fc-receptor-mediated phagocytosis of SRBC. In the bactericidal assay, bacterial growth, after 1 hr without macrophages, was 31 X 10(3) colony-forming units (CFU). In the presence of PAMs from splenectomized rats, the colony count was 22 X 10(3) (P less than 0.2). Bactericidal activity was highly evident when PAMs from control and autotransplanted rats were assayed, with CFU of 11.3 X 10(3) and 14.6 X 10(3), respectively (P less than 0.001, P less than 0.002, respectively). It is concluded that antibody-dependent and independent phagocytic activity of PAMs is unimpaired in splenectomized rats as compared to controls. The defect in rats splenectomized at 1 week of age resides in poor pneumococcal bactericidal activity of PAMs and is almost completely corrected by ip autotransplantation of one-third of the spleen.