摘要篇首： Sporothrix schenckii (S. schenckii), a dimorphic fungus, is the etiological agent of sporotrichosis. After entrance of microconidia or mycelial fragments into a mammalian host, the fungus differentiates into the parasitic yeast form. Meanwhile, several defensive signals would be triggered when the innate immune system was stimulated by 5. schenckii invasion and microbe-specific phagocytosis. The success of 5. schenckii infection partly depends on its ability to avoid oxidative damage from reactive oxygen species (ROS) released by polymorphonuclear leukocytes and activated macrophages. However, the antioxidant defense mechanisms of S. schenckii remains unknown. Catalases, one of the central enzymes involved in scavenging ROS via converting hydrogen peroxide (H2O2) to water and molecular oxygen, play an essential role in protecting intracellular pathogenic fungi against ROS1,2 and regulating growth and development in some fungi.3'4 No catalase in 5. schenckii has been identified and characterized previously. Recently we have cloned a catalase homologous gene from the yeast form of 5. schenckii and designated it Sscat. In this report, we used quantitative real-time polymerase chain reaction (PCR) to measure and compare mRNA expression of Sscat in the mycelium-to-yeast transition and H2O2-challenge induced microenvironments in vitro. The results presented may help in understanding the role of 5. schenckii catalase in the fungus-host interaction with respect to ROS.