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Chlamydicidal activity of human alveolar macrophages
M N Nakajo1, P M Roblin, M R Hammerschlag
1Department of Pediatrics, State University of New York, Brooklyn 11203.
Abstract:
Pneumonia due to Chlamydia trachomatis is a disease limited mainly to infants under 6 months of age. Rare cases have been reported in immunocompromised adults. One possible reason for the propensity of the pneumonia to occur in the very young may be related to differences in the phagocytic and bactericidal capacity of alveolar macrophages (AMs) in young infants and adults. At birth a function of AMs is clearance of surfactant-related material from the alveolar surface. Studies in animals have suggested that engorgement of AMs with surfactant-related lipids may reduce the microbicidal capacity of these cells. In the present study we determined that AMs obtained from healthy, nonsmoking adults were capable of killing both human biovars of C. trachomatis, with complete killing observed by 48 h after inoculation. Preincubation of AMs from adults with surfactant did not reduce the capacity of the cells to kill C. trachomatis.
Insights
Alveolar macrophages from adults effectively kill Chlamydia trachomatis. Surfactant presence did not impair this bacterial killing capacity in adult lung cells, suggesting other factors may influence infant susceptibility to this pneumonia.
Area of Science:
- Immunology
- Infectious Diseases
- Pulmonary Medicine
Background:
- Infant pneumonia is often caused by Chlamydia trachomatis, with rare adult cases primarily in immunocompromised individuals.
- Alveolar macrophages (AMs) in infants may have reduced phagocytic and bactericidal capacity compared to adults.
- Surfactant accumulation in infant AMs is hypothesized to impair microbicidal function.
Purpose of the Study:
- To investigate the bactericidal capacity of adult alveolar macrophages against Chlamydia trachomatis.
- To determine if surfactant affects the ability of adult AMs to kill Chlamydia trachomatis.
Main Methods:
- Isolation of alveolar macrophages from healthy, nonsmoking adults.
- Inoculation of adult AMs with human biovars of Chlamydia trachomatis.
- Incubation of adult AMs with surfactant prior to or during Chlamydia trachomatis challenge.
Main Results:
- Adult alveolar macrophages demonstrated effective killing of both human biovars of Chlamydia trachomatis.
- Complete clearance of Chlamydia trachomatis was observed within 48 hours post-inoculation.
- Preincubation of adult AMs with surfactant did not diminish their capacity to kill Chlamydia trachomatis.
Conclusions:
- Adult alveolar macrophages possess robust bactericidal activity against Chlamydia trachomatis.
- Surfactant does not appear to inhibit the microbicidal function of adult alveolar macrophages.
- Factors other than surfactant-mediated impairment of adult AMs likely contribute to the higher incidence of Chlamydia trachomatis pneumonia in infants.