As it is known that Nude mice have equal amount of Ig-M with normal mice (Bloemmen and Eyssen, 1973; Mink et al., 1980), and Nude mice can produce viral specific IgG (Suckling et al., 1982), the presence of B lymphocytes in Nude and Nude-J mice may prevent the mice from some infection in these highly mice. This evidence concerns the gene CD40LG and infection.