Streptococcal Skin Infection Air Pouch Model

Groups of six WT, IL-33-KO, and ST2-KO mice were anesthetized by isoflurane inhalation and then injected subcutaneously with 1 mL of air to form an air pouch one day before the infection. One day later, 0.1 mL of bacterial suspension containing 3 × 10⁸ S. pyogenes NZ131 cells was inoculated into the air pouch [48 (link)]. The animals were observed every day for a total of 13 days. Survival curves were then determined. At 48 h post-infection, the degrees of skin lesion were quantitated by an exudates-absorbed method, which is based on the premise that the more severe the skin damage, the more that the exudates will effuse. A Kimwipes (Kimberly-Clark Global Sales, Inc., Roswell, GA, USA) paper was attached to the air pouch area, and the wet area of the paper was then gauged [49 (link)]. The average lesion area in each group was generated by examination of skin lesions from six mice. After that, the skin lesion tissue around the air pouch was excised, fixed in 3.7% formaldehyde, and embedded in paraffin. The 5-µm-thick tissues were sliced and stained with hematoxylin and eosin. In some experiments, 0.1 mL of mouse rIL-33 (R&D Systems) (1 µg per mouse) and sST2 protein (R&D Systems) (1 µg per mouse) were injected into the air pouches of IL-33-KO mice and WT mice, respectively, at 30 min before GAS infection or 24 h post-infection.