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Updated: Jun 23, 2026
A Non-invasive and Technically Non-intensive Method for Induction and Phenotyping of Experimental Bacterial Pneumonia in Mice
Published on: September 28, 2016
Evaluation of a novel therapeutic approach to treating severe pneumococcal infection using a mouse model
Nikkol Melnick1, Gowrisankar Rajam, George M Carlone
1Division of Bacterial Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA.
Abstract:
P4, a 28-amino-acid peptide, is a eukaryotic cellular activator that enhances specific in vitro opsonophagocytic killing of multiple bacterial pathogens. In a previous study, we successfully recreated this phenomenon in mice in vivo by using a two-dose regimen of P4 and pathogen-specific antibodies, which significantly reduced moribundity in mice. For the present study, we hypothesized that the inclusion of a low-dose antibiotic would make it possible to treat the infected mice with a single dose containing a mixture of P4 and a pathogen-specific antibody. A single dose consisting of P4, intravenous immunoglobulin (IVIG), and ceftriaxone effectively reduced moribundity compared to that of untreated controls (n = 10) by 75% (P < 0.05) and rescued all (10 of 10) infected animals (P < 0.05). If rescued animals were reinfected with Streptococcus pneumoniae and treated with a single dose containing P4, IVIG, and ceftriaxone, they could be rerescued. This observation of the repeated successful use of P4 combination therapy demonstrates a low risk of tolerance development. Additionally, we examined the polymorphonuclear leukocytes (PMN) derived from infected mice and observed that P4 enhanced in vitro opsonophagocytic killing (by >80% over the control level; P < 0.05). This finding supports our hypothesis that PMN are activated by P4 during opsonophagocytosis and the recovery of mice from pneumococcal infection. P4 peptide-based combination therapy may offer an alternative and rapid immunotherapy to treat fulminant pneumococcal infection.
Insights
P4 peptide therapy, combined with antibodies and antibiotics, effectively treated severe pneumococcal infections in mice. This P4 combination therapy demonstrated rapid efficacy and a low risk of tolerance, offering a potential immunotherapy for serious bacterial infections.
Area of Science:
- Immunology
- Microbiology
- Pharmacology
Background:
- P4 peptide activates eukaryotic cells, enhancing the killing of bacterial pathogens.
- Previous studies showed P4 and antibodies reduced mouse mortality in a two-dose regimen.
- This study investigated a single-dose combination therapy for enhanced treatment efficacy.
Purpose of the Study:
- To evaluate the efficacy of a single-dose P4, intravenous immunoglobulin (IVIG), and ceftriaxone combination therapy in treating Streptococcus pneumoniae infection in mice.
- To assess the potential for tolerance development with repeated P4 combination therapy.
- To investigate the mechanism of P4 action on polymorphonuclear leukocytes (PMN) during infection.
Main Methods:
- Mice infected with Streptococcus pneumoniae were treated with a single dose of P4, IVIG, and ceftriaxone.
- Rescued mice were reinfected and retreated to assess re-rescue and tolerance.
- Polymorphonuclear leukocytes (PMN) from infected mice were analyzed for P4-mediated effects on opsonophagocytic killing in vitro.
Main Results:
- A single dose of P4, IVIG, and ceftriaxone reduced mortality by 75% and rescued all infected animals.
- Repeated treatment of reinfected mice with the same combination therapy was successful, indicating a low risk of tolerance.
- P4 significantly enhanced in vitro opsonophagocytic killing by PMN by over 80%.
Conclusions:
- P4 peptide-based combination therapy with IVIG and ceftriaxone is a highly effective single-dose treatment for severe pneumococcal infections in mice.
- The therapy shows promise for rapid immunotherapy with a low risk of tolerance development.
- P4 activates PMN, contributing to enhanced bacterial clearance and animal recovery.
