The fall flu season is coming. It is time to get your flu shot! Many people may still remember the influenza A H1N1 flu ("swine flu") pandemic of 2009, which caused 280,000 deaths worldwide. The best way to prevent the flu is to get vaccinated with a flu shot or use the flu nasal spray vaccine. However, rapid evolution of the flu virus constantly requires new vaccines. Fortunately, the immune system has several defensive mechanisms in the lung to clear inhaled pathogens. One of these mechanisms involves surfactant proteins which induce aggregation of viral particles and, thereby, prevent infection, serving as a front-line host defense. Recently, researchers found that surfactant protein D (SP-D) from pigs exhibits particularly strong inhibitory activity, more so that human SP-D. This discovery leads researchers to investigate SP-D structure-related antiviral activity. In a recent experimental-simulation study, crystallographic analysis of pig and human SP-D showed that a loop involved in viral binding on pig SP-D is longer than the respective loop on human SP-D; molecular dynamics simulation revealed that the longer loop of pig SP-D has higher flexibility than that of human SP-D, suggesting that the flexible loop region could facilitate strong binding of SP-D to virus. Based on this finding, one can develop new nasal spray anti-flu protection through other structural modification of human lung surfactant proteins. More on our lung surfactant protein website.