The serum positive rates of SEA specific IgG on days 0, 7, 10, 14, 18, 21 and 28 post-infection were 0, 20, 20, 30, 50, 70 and 90% respectively; and the serum positive rates of SEA specific IgM at the same times post-infection were 0, 10, 20, 30, 50, 70 and 100%, respectively (Table 2). Here, CD40LG is linked to infection.