Clearance of Bordetella parapertussis from the lower respiratory tract requires humoral and cellular immunity

Abstract

Bordetella parapertussis and Bordetella pertussis are closely related species that cause whooping cough, an acute, immunizing disease. Their coexistence in the same host populations at the same time and vaccine studies showing that B. pertussis vaccines have little effect on B. parapertussis infection or disease suggest that the protective immunity induced by each does not efficiently cross protect against the other. Although the mechanisms of protective immunity to B. pertussis have been well studied, those of B. parapertussis have not. The present study explores the mechanism by which B. parapertussis is cleared from the lower respiratory tract by anamnestic immunity. Serum antibodies are necessary and sufficient for elimination of this bacterium, and CD4(+) T cells, complement, and neutrophils are required for serum antibody-mediated clearance. Mice lacking immunoglobulin A had no defect in their ability to control or clear infection. Interestingly, serum antibody-mediated clearance of B. parapertussis did not require Fc receptors that are required for antibody-mediated clearance of B. pertussis. Together these data support a model for the mechanism of protective immunity to B. parapertussis that is similar but distinct from that of B. pertussis.

FIG. 1.

Adaptive immunity is required for prevention of systemic spread and death due to B. parapertussis infection. Groups of 10 C57BL/6 (C57) (▪), 10 RAG2^−/− (X), 10 μMT (⧫), and 10 TCR-α^−/− (▴) mice were intranasally inoculated with 5 × 10⁵ CFU of B. parapertussis in 50 μl of PBS for a survival curve (A). Separate groups of four similarly inoculated mice of each strain were sacrificed at day 28 to measure colonization of the lungs (B) and blood (C). The number of bacteria recovered from each tissue is expressed as the log₁₀ mean ± standard deviation (error bar). Values that were significantly different from those for wild-type C57BL/6 mice (P values of less than 0.05) are indicated by asterisks. The dashed line represents the limit of detection.

FIG. 2.

Mice deficient in Ab production are unable to clear B. parapertussis from the LRT. Groups of 24 C57BL/6 (▪), RAG2^−/− (X), μMT (⧫), and TCR-α^−/− (▴) mice were inoculated as described in the legend to Fig. 1 and sacrificed on days 7, 14, 28, 49, 70, and 105 (A). The numbers of bacteria are expressed as the log₁₀ means ± standard deviations (error bars). Pooled serum samples were taken from C57BL/6 (black bars), μMT (white bars), and TCR-α^−/− (hatched bars) mice sacrificed on day 28 for quantification of anti-B. parapertussis (anti-Bpp) antibodies via an ELISA (B). Dashed lines represent the limit of detection.

FIG. 3.

Mucosal antibodies are not crucial to clearance of B. parapertussis from the LRT. Groups of 24 C57BL6 (▪) and IgA^−/− (♦) mice were inoculated as described in the legend to Fig. 1 and sacrificed on days 7, 14, 28, 49, 70, and 105. The numbers of bacteria are expressed as log₁₀ means ± standard deviations (error bars). The dashed line represents the limit of detection.

FIG. 4.

T cells are required for the function of serum antibodies in clearing B. parapertussis from the LRT. Four control C57BL/6 (C57) mice were given an i.p. injection of naïve serum (NS) at the time of intranasal inoculation with B. parapertussis as described in the legend to Fig. 1. Groups of four C57BL/6, RAG2^−/−, μMT, and TCR-α^−/− mice were given i.p. injections of immune serum (IS) at the time of inoculation. Groups of four C57BL/6 mice were given i.p. injections of anti-CD4 (αCD4) or anti-CD8 (αCD8) antibody in addition to immune serum at the time of inoculation. All mice were sacrificed on day 14. The numbers of bacteria are expressed as the log₁₀ means ± standard deviations (error bars). Values that were significantly different from those for wild-type C57BL/6 mice (P values of less than 0.05) are indicated by asterisks. The dashed line represents the limit of detection.

FIG. 5.

Complement is required for the function of serum antibodies against B. parapertussis. Four control C57BL/6 (C57) mice were given i.p. injections of naïve serum (NS) upon inoculation with B. parapertussis as described in the legend to Fig. 1. Groups of four C57BL/6, C3^−/−, C5^−/−, CD11b^−/−, and FcR-γ^−/− mice were injected i.p. with immune serum (IS) at the time of inoculation. All mice were sacrificed on day 14. The numbers of bacteria are expressed as the log₁₀ means ± standard deviations (error bars). Values that were significantly different from those for wild-type C57BL/6 mice (P values of less than 0.05) are indicated by asterisks. The dashed line represents the limit of detection.

FIG. 6.

Neutrophils are required for the function of serum antibodies against B. parapertussis. Four control μMT mice were injected i.p. with naïve serum (NS) upon inoculation as described in the legend to Fig. 1. Four μMT mice were injected i.p. with immune serum (IS) upon inoculation. Four μMT mice were injected with the monoclonal antibody RB6-8C5 (RB6) to deplete neutrophils 24 h prior to and 7 days after infection and injected with immune serum upon inoculation. All mice were sacrificed on day 14. The numbers of bacteria are expressed as the log₁₀ means ± standard deviations (error bars). Values that were significantly different from those for wild-type C57BL/6 mice (P values of less than 0.05) are indicated by asterisks. The dashed line represents the limit of detection.