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The quantity and function of pulmonary alveolar macrophages after splenectomy and Corynebacterium parvum
Abstract:
We have previously shown that Corynebacterium parvum (C. parvum), a nonspecific immunomodulator, partially protects splenectomized and nonsplenectomized mice when challenged with aerosolized pneumococci. We report here the effects of both splenectomy and C. parvum on the phagocytic function of the lavageable pulmonary alveolar macrophage (PAM). Groups of young adult male Sprague Dawley rats underwent splenectomy or sham operation 3 weeks before injection of C. parvum 1.5 mg IP (or saline) per animal. One week postinjection PAM's were harvested. The in vitro phagocytic indices (PI) for PAM incubated with tritiated thymidine-labeled S. aureus or Streptococcus pneumoniae, type 14, opsonized with normal rat serum, were determined. Splenectomy had no effect on lung weights, PAM yield, or PAM phagocytic activity. C. parvum administration significantly increased spleen weight in sham-operated animals, but had no effect on lung weights, PAM yield, or phagocytic activity of either control or splenectomized animals. Splenectomy in the adult rat did not induce a phagocytic defect in the PAM and thus the lavageable PAM cannot be considered a significant site of the postsplenectomy defect. Since C. parvum protects animals from respiratory challenge with Streptococcus pneumoniae but does not alter the number or activity of lavageable alveolar macrophages, we hypothesize that C. parvum protection is more likely related to our previous finding of an increased clearance of blood-borne bacteria by the expanded and enhanced reticuloendothelial system.
Insights
Splenectomy did not impair pulmonary alveolar macrophage phagocytic function in rats. Corynebacterium parvum also did not affect macrophage activity, suggesting its protective effects against pneumococci involve other immune mechanisms.
Area of Science:
- Immunology
- Pulmonary Medicine
- Microbiology
Background:
- Nonspecific immunomodulators like Corynebacterium parvum (C. parvum) offer partial protection against pneumococcal challenges.
- The role of splenectomy and C. parvum in modulating pulmonary alveolar macrophage (PAM) phagocytic function remains unclear.
Purpose of the Study:
- To investigate the impact of splenectomy and C. parvum administration on the phagocytic capacity of lavageable pulmonary alveolar macrophages (PAMs).
- To determine if PAMs are a significant site of the postsplenectomy defect in host defense against respiratory pathogens.
Main Methods:
- Adult male Sprague Dawley rats underwent splenectomy or sham operation.
- Animals were subsequently injected with C. parvum or saline.
- Pulmonary alveolar macrophages (PAMs) were harvested one week post-injection.
- In vitro phagocytic indices (PI) were determined for PAMs incubated with opsonized Staphylococcus aureus and Streptococcus pneumoniae.
Main Results:
- Splenectomy did not alter lung weights, PAM yield, or PAM phagocytic activity.
- C. parvum administration increased spleen weight in sham-operated rats but did not affect lung weights, PAM yield, or phagocytic activity in either splenectomized or control animals.
- The phagocytic activity of lavageable PAMs was not impaired by splenectomy.
Conclusions:
- Splenectomy in adult rats does not induce a phagocytic defect in pulmonary alveolar macrophages (PAMs).
- C. parvum does not enhance the phagocytic activity or number of lavageable PAMs.
- The protective effect of C. parvum against Streptococcus pneumoniae is likely mediated by enhanced clearance of blood-borne bacteria via the reticuloendothelial system, rather than through alveolar macrophage activation.