Development of T-B cell collaboration in neonatal mice

The neonatal immune response is impaired during the first weeks after birth . To obtain a better understanding of this immaturity, we investigated the development of T cell interactions with B cells in mice. For this purpose, we analyzed the immune response to three T-dependent antigens in vivo: (i) the polyclonal antibody response induced by vaccinia virus; (ii) the produc tion of polyclonal and specific antibodies following immunization with hapt en-carrier conjugates; (iii) the mouse mammary tumor virus superantigen (sA g) response involving an increase in sAg-reactive T cells and induction of polyclonal antibody production. After vaccinia virus injection into neonate s, the polyclonal antibody response was similar to that observed in adult m ice. The antibody response to hapten-carrier conjugates, however, was delay ed and reduced. Injection with sAg-expressing B cells from neonatal or adul t mice allowed us to determine whether a cells, T cells or both were implic ated in the reduced immune response. In these sAg responses, neonatal T cel ls were stimulated by both neonatal and adult sag-presenting B cells but on ly B cells from adult mice differentiated into IgM- and IgG-secreting plasm a cells in the neonatal environment in vivo. Injecting neonatal B cells int o adult mice did not induce antibody production. These results demonstrate that the environment of the neonatal lymph node is able to support a T and a cell response, and that immaturity of B cells plays a key role in the red uced immune response observed in the neonate.