Giardia lamblia is one of the most common protozoan infectious agents in the world and is responsible for diarrheal disease and chronic postinfectious illness. During the host-parasite interaction, proteases are important molecules related to virulence, invasion, and colonization, not only for Giardia but also for other parasites. We aimed to characterize the cysteine protease activity detected in trophozoite lysates. This proteolytic activity showed the ability to cleave NH-terminal sequences with either a recognition sequence for a viral protease or a recognition sequence for thrombin. This cleavage activity was detected in nonencysting trophozoites and increased with the progression of encystation. This activity was also detected in excretion/secretion products of axenic trophozoites and in trophozoites cocultured with differentiated Caco-2 cells. Based on size exclusion chromatography, we obtained a fraction enriched in low- to medium-molecular-weight proteins that was capable of exerting this cleavage activity and aggregating human platelets. Finally, our results suggest that this proteolytic activity is shared with other protozoan parasites.

贾第鞭毛虫是世界上最常见的原生动物感染因子之一，并负责腹泻病和慢性感染后疾病。在宿主与寄生虫的相互作用中，蛋白酶是与毒力，入侵和定殖有关的重要分子，不仅对于贾第虫而且还用于其他寄生虫。我们旨在表征在滋养体裂解物中检测到的半胱氨酸蛋白酶活性。这种蛋白水解活性显示了用病毒蛋白酶的识别序列或凝血酶的识别序列切割NH-末端序列的能力。这种切割活性是在非侵入性滋养体中检测到的，并随着侵入过程的进行而增加。也可以在轴突滋养体的排泄/分泌产物中以及与分化的Caco-2细胞共培养的滋养体中检测到这种活性。基于尺寸排阻色谱，我们获得了富含低分子量至中分子量蛋白质的馏分，该蛋白质能够发挥这种裂解活性并聚集人血小板。最后，