2.4. Rat Paw Swelling, Body Weight, and Sample Collection

The degree of joint swelling was measured on days 0, 1, 2, 5, 8, 11, 14, 17, 20, 23, 26, and 29 after immunization. The toe volume of the inflammation side (left hind paw) of the rat was measured using a rat paw volume plethysmometer (Model: 37140 Ugo Basile, Italy), and the result was expressed as the volume of water displaced below the left ankle joint [28]. Rats were weighed once every 5 days after immunization. Six hours after the gavage on the 29th day, the rats were anesthetized by intraperitoneal injection of 10% chloral hydrate and blood was taken from the abdominal aorta. After rats were sacrificed (decapitation under chloral hydrate), the left ankle joints were separated, partially stored in a −80 degree refrigerator, and partially immersed in 4% neutral paraformaldehyde (Solarbio, Beijing, China).