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Immunologic responses of children to serious infections with Streptococcus pneumoniae
Insights
Children infected with Streptococcus pneumoniae showed weak antibody responses and evidence of immune complex formation. Complement levels were often depressed, indicating significant immune system activation during infection.
Area of Science:
- Immunology
- Pediatrics
- Infectious Diseases
Background:
- Streptococcus pneumoniae is a leading cause of meningitis and bacteremia in children.
- Understanding the immune response to pneumococcal infections is crucial for managing disease severity and outcomes.
Purpose of the Study:
- To evaluate antibody responses, complement system alterations, and circulating immune complexes in children post-Streptococcus pneumoniae infection.
- To assess the dynamics of these immune markers during the course of illness and recovery.
Main Methods:
- Radioimmunoassay for antibody levels.
- Fluid-phase C1Q-binding assay, fluid-phase conglutinin assay, and C1 activation assays for immune complexes.
- Measurement of serum complement components (C3, C4, Factor B).
Main Results:
- Transient and often weak homotypic antibody responses were observed in 25% of children.
- 53% exhibited heterotypic antibody responses to non-infecting S. pneumoniae serotypes.
- Early C1 activation and C1q-binding activity were transient; positive conglutinin assay results were common later in the disease course (93%).
- Depressed levels of complement components C4 (9 children), C3 (4 children), and Factor B (2 children) were noted.
Conclusions:
- Children infected with Streptococcus pneumoniae mount a complex immune response characterized by limited specific antibody production and significant immune complex formation.
- Complement system activation and consumption are prominent features of pneumococcal meningitis and bacteremia in children.
- The persistent positive conglutinin assay suggests ongoing immune complex deposition or activation of the classical complement pathway during convalescence.
Abstract:
Antibody responses (as measured by radioimmunoassay), alterations in serum levels of complement, and the presence of circulating immune complexes (as measured by the fluid-phase C1Q-binding assay, the fluid-phase conglutinin assay, and the activation of C1 were evaluated in 15 children after meningitis and/or bacteremia caused by Streptococcus pneumoniae. The ages of the children ranged from two months to 16 years; the duration of follow-up ranged from 18 to 189 days (mean, 78 days). Increases in levels of homotypic antibody were found in only three (25%) of the 12 children in whom this response could be assessed, and all of these responses were transient. Eight (53%) of the 15 children had evidence of a heterotypic antibody response to S pneumoniae serotypes other than those causing their infections. The activation of C1 and C1q-binding activity were detected at the early stage of disease and were generally transient. The result of the fluid-phase conglutinin assay was positive for 14 (93%) of the 15 children later in the course of disease; this result was consistently positive throughout the follow-up period in the majority of children. Depressed concentrations of C4 were noted in nine children, depressed levels of C3 in four, and depressed levels of factor B in two.