Abstract
Influenza virus evolves constantly in an unpredictable fashion, making it necessary to vaccinate people annually for effective prevention and control of influenza. In general, however, during the first wave of an influenza outbreak caused by a newly emerging virus strain, influenza morbidity and mortality have been observed to rise sharply due to the lack of a matching vaccine. This necessitates the exploration of novel intervention approaches, particularly those prophylactic or therapeutic agents that have a broad range of antiviral activities and are also proven to be non-toxic. Here, we reported that stimulation of the innate immune system by intranasal administration of chitosan as a single agent was sufficient to completely protect BALB/c mice from lethal infection by H7N9 virus, a newly emerged viral strain that is highly pathogenic to humans. Remarkably, animals could still be protected against lethal challenge by H7N9 (10×LD50), even ten days after the intranasal chitosan administration. The significantly enhanced infiltration of leukocytes in the bronchoalveolar lavage and elevated levels of proinflammatory cytokines in the bronchia/lung tissues revealed the potent activation of mucosal immune responses by intranasally delivered chitosan. We also observed that chitosan can protect mice from three other virus strains. The marked breadth and magnitude of protection against diverse viral strains makes chitosan an attractive candidate as a universal anti-influenza agent.
Highlights
While it is well established that neutralizing antibodies and cytotoxic T lymphocytes (CTL) largely contribute to specific immune responses against the influenza virus[15,16], innate immunity plays a significant role in host defenses against it
To investigate whether intranasal administration of chitosan in BALB/c mice could protect mice against H7N9 influenza virus infection, various doses of chitosan were given to mice via the intranasal (i.n.) or intraperitoneal route (i.p.) (Table 1)
As overall survival rates were monitored over 21 days, we determined the virus replication in mice three days after the H7N9 viral challenge; we found the viral loads in trachea/lung tissues from chitosan-treated mice were significantly lower than that from the control group J (p value of group A to E were
Summary
While it is well established that neutralizing antibodies and cytotoxic T lymphocytes (CTL) largely contribute to specific immune responses against the influenza virus[15,16], innate immunity plays a significant role in host defenses against it. In groups G and H, the mice were dosed twice with 30 or 10 μg chitosan (i.n) and challenged 3 days after the second chitosan administration. In group I, the animals were dosed twice with 100 μg chitosan via the intraperitoneal route (i.p.) and were challenged 3 days after the second chitosan administration. In all viral challenge groups, the mice were infected with a lethal dose of A/Shanghai/2/2013(H7N9) (10×LD50) or A/Puerto Rico/8/34 (H1N1) (10×LD50) to determine the protective effect; the animals were observed for 21 days. We report that intranasal administration of chitosan alone could completely protect BALB/c mice from lethal H7N9 viral challenges, an observation that is reproduced using three other subtypes of influenza viruses as challenging pathogens
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