Neutralizing anti-F glycoprotein and anti-substance P antibody treatment effectively reduces infection and inflammation associated with respiratory syncytial virus infection

Abstract

Respiratory syncytial virus (RSV) is the most important virus mediating lower respiratory tract illness in infants and young children. RSV infection is associated with pulmonary inflammation and increased levels of substance P (SP), making the airways and leukocytes that express SP receptors susceptible to the proinflammatory effects of this peptide. This study examines combining neutralizing anti-F glycoprotein and anti-SP antibody treatment of RSV-infected BALB/c mice to inhibit RSV replication and inflammation associated with infection. BALB/c mice were prophylactically treated with antibody prior to RSV infection or were therapeutically treated at day 2 or 6 post-RSV infection. Prophylactic or therapeutic treatment with anti-SP antibodies promptly reduced pulmonary inflammatory cell infiltration and decreased the number of cells expressing proinflammatory cytokines, while anti-F antibody treatment reduced virus titers. The results suggest that combined anti-viral and anti-SP antibody treatment may be effective in treating RSV disease.

FIG. 1.

Prophylactic treatment. Shown are flow cytometry results following prophylactic treatment (day −1 prior to infection) of mice with anti-SP and anti-F antibodies. (A) Total pulmonary leukocyte trafficking. (B to F) BAL were stained with antibodies against CD8⁺ (B), CD4⁺ (C), B220⁺ (D), and CD11b⁺ (E) cells and PMN (RB6-8C5⁺) (F). The data are expressed as the mean number (10³) of BAL/lung (± SEM) on days 3, 5, and 7 p.i. from three independent experiments. Asterisks indicate a significant difference (P < 0.05) between nIg-treated and antibody-treated mice.

FIG. 2.

Early therapeutic treatment. Shown are flow cytometry results following early (day 2 p.i.) therapeutic treatment of mice with anti-SP and anti-F antibodies. (A) Total pulmonary leukocyte trafficking. (B to F) BAL were stained with antibodies against CD8⁺ (B), CD4⁺ (C), B220⁺ (D), and CD11b⁺ (E) cells and PMN (RB6-8C5⁺) (F). The data are expressed as the number (10³) of BAL/lung (± SEM) on days 3, 5, and 7 p.i. A representative experiment from two independent experiments is shown. Asterisks indicate a significant difference (P < 0.05) between nIg-treated and antibody-treated mice.

FIG. 3.

Late therapeutic treatment. Shown are flow cytometry results following late (day 6 p.i.) therapeutic treatment of mice with anti-SP and anti-F antibodies. (A) Total pulmonary leukocyte trafficking. (B to F) BAL were stained with antibodies against CD8⁺ (B), CD4⁺ (C), B220⁺ (D), and CD11b⁺ (E) cells and PMN (RB6-8C5⁺) (F). The data are expressed as the number (10³) of BAL/lung (± SEM) on days 3, 5, 7, and 9 p.i. A representative experiment from two independent experiments is shown. Asterisks indicate a significant difference (P < 0.05) between nIg-treated and antibody-treated mice.

FIG. 4.

RSV lung titers following antibody treatment. The lungs of antibody treated-mice were harvested on days 3, 5, 7, and 9 post-RSV infection. (A) Prophylactic antibody treatment 1 day prior to infection. (B) Early therapeutic antibody treatment on day 2 p.i. (C) Late therapeutic antibody treatment on day 6 p.i. The results are expressed as 10³ PFU/g (+ SEM).

FIG. 5.

SP levels in BAL. Mice were treated on day −1 prior to infection (A) or day 2 (B) or day 6 (C) p.i. with either nIg, anti-SP, anti-F, or anti-SP/F antibody. Cell-free BAL lavage fluid was harvested on days 3, 5, 7, and 9 p.i. and examined for levels of SP by enzyme-linked immunosorbent assay. The dashed lines represent the mean baseline SP concentration in the BAL from naïve mice. The data are expressed as the SP concentration (in picograms per milliliter) (+ SEM).