INDUCTION OF PROTECTIVE CTL RESPONSES IN NEWBORN MICE BY A MURINE RETROVIRUS

The susceptibility of neonates to virus-induced disease is thought to reflect, in part, the immaturity of their immune systems. However, ino culation of newborn mice with low doses of Cas-Br-M murine leukemia vi rus induced a protective cytotoxic T lymphocyte (CTL) response. The in ability of neonates to develop a CTL response to high doses of virus w as not the result of immunological immaturity but correlated with the induction of a nonprotective type 2 cytokine response. Thus, the initi al viral dose is critical in the development of protective immunity in newborns.