Neuropsychological syndromes including schizophrenia often do not manifest until late adolescence or early adulthood. Studies attributing a role in brain maintenance to the immune system led us to propose that malfunction of immune-dependent regulation of brain functions at adolescence underlies the late onset of such diseases/syndromes. One such function is sensorimotor gating, the ability to segregate a continuous stream of sensory and cognitive information, and to selectively allocate attention to a significant event by silencing the background (measured by prepulse inhibition; PPI). This activity is impaired in schizophrenia, as well as in several other neuropsychological diseases. Using a model of prenatal immune activation (maternal polyriboinosinic-polyribocytidylic acid (poly I:C) injection), often used as a model for schizophrenia, and in which abnormal PPI has a delayed appearance, we demonstrated a form of immune deficit in the adult offspring. Similar abnormal PPI with a delayed appearance was found in congenitally immune-deficient mice (severe combined immune deficient, SCID), and could be reversed by immune reconstitution. This functional deficit correlated with impairment of both hippocampal neurogenesis and expression of the gene encoding kisspeptin (Kiss1) that manifested at adulthood. Moreover, exogenous administration of a kisspeptin-derived peptide partially reversed the gating deficits in the SCID mice. Our results suggest that a form of congenital immune deficiency may be a key factor that determines manifestation of developmental neuropsychological disorders with onset only at early adulthood.