Compared with the unchallenged birds, E. coli challenge significantly (P < 0.05) resulted in an increase in the serum concentration of IgA and IgM at the early stage of infection at d 14 (at 3 d postinfection), but the serum IgA and IgM level were decreased and significantly lower than unchallenged birds at 21 d (at 10 d postinfection). The gene discussed is CD40LG; the disease is infection.