RESUMEN
Viruses, including retroviruses, can be passed from mothers to their progeny during birth and breastfeeding. It is assumed that newborns may develop immune tolerance to milk-transmitted pathogens similarly to food antigens. I/LnJ mice are uniquely resistant to retroviruses acquired as newborns or as adults as they produce virus-neutralizing antibodies (Abs). A loss-of-function allele of H2-Ob (Ob), originally mapped within the virus infectivity controller 1 (vic1) locus, is responsible for production of antiretrovirus Abs in I/LnJ mice. Importantly, Ob-deficient and vic1 I/LnJ congenic mice on other genetic backgrounds produce antivirus Abs when infected as adults, but not as newborns. We report here that I/LnJ mice carry an additional genetic locus, virus infectivity controller 2 (vic2), that abrogates neonatal immune tolerance to retroviruses. Further genetic analysis mapped the vic2 locus to the telomeric end of chromosome 15. Identification of the vic2 gene and understanding of the related signaling pathways would make blocking of neonatal immune tolerance to retroviruses an achievable goal.IMPORTANCE This work describes a previously unknown genetic mechanism that allows neonates to respond to infections as efficiently as adults.