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Minimum protective serum concentrations of pneumococcal anti-capsular antibodies in infant rats
A M Stack1, R Malley, C M Thompson
1Department of Medicine, Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
Insights
Pneumococcal anticapsular antibodies protect infant rats against Streptococcus pneumoniae infection. Specific antibody levels significantly reduced mortality, demonstrating their protective capacity in a pulmonary infection model.
Area of Science:
- Immunology
- Infectious Diseases
- Pediatric Research
Background:
- Streptococcus pneumoniae causes severe infections in infants.
- Pneumococcal anticapsular antibodies are crucial for protection.
- Infant immune responses may differ in their capacity to combat pneumococcal infections.
Purpose of the Study:
- To evaluate the protective efficacy of passive immunization with pneumococcal anticapsular antibodies in infant rats.
- To determine the required serum antibody concentrations for protection against various Streptococcus pneumoniae serotypes.
- To assess the impact of antibodies on mortality in a model of pneumococcal pulmonary infection.
Main Methods:
- Passive immunization of infant rats with type-specific anticapsular antibody sera.
- Challenge inoculation with animal-passaged Streptococcus pneumoniae strains (serotypes 1, 4, 5, 6b, 7f, 9v, 14, 18c, 19f, 23f).
- Assessment of mortality, bacteremia, meningitis, and histologic lung changes.
Main Results:
- A serum antibody concentration of 0.1-1.15 microg/mL significantly reduced mortality for most serotypes.
- Serotype 14 required a higher antibody concentration (2.32 microg/mL) for significant mortality reduction.
- The serum antibody level for 50% mortality reduction ranged from 0.1-3.5 microg/mL across all tested serotypes.
Conclusions:
- Pneumococcal anticapsular antibodies confer significant protection against invasive pneumococcal disease in infant rats.
- Antibody efficacy varies by serotype, with some requiring higher concentrations for protection.
- These findings support the role of anticapsular antibodies in preventing severe pneumococcal infections in infants.
Abstract:
Infant rats were passively immunized to determine the protective capacity of pneumococcal anticapsular antibodies. Animal-passaged strains of Streptococcus pneumoniae serotypes 1, 4, 5, 6b, 7f, 9v, 14, 18c, 19f, and 23f were used as challenge inocula (1-1500 cfu) in a model of pulmonary infection that resulted in bacteremia, meningitis, and death. From untreated control animals, histologic sections of lung demonstrated infiltrative pneumonia and lung homogenate cultures grew S. pneumoniae at concentrations of 10(3)-10(8) cfu per gram of lung tissue. A type-specific anti-capsular antibody serum concentration of 0.1-1.15 microg/mL resulted in a statistically significant reduction in mortality compared with the reduction in untreated controls, except for serotype 14, which required 2.32 microg/mL for a significant reduction in mortality. The serum antibody level that provided 50% reduction in mortality ranged from 0.1-3.5 microg/mL for all serotypes.