A) Timeline of experiments. The Open field test (OFT), Social Interaction (SI), and Sucrose Preference Test (SPT) were conducted during the adolescent period (PND 35 – 41). The Morris Water Maze (MWM) took place when mice had reached adulthood (PND 84). In parallel, expansion and colonization of the brain by GFP+ lymphocytes was assessed at 2, 4, 8 and 12 weeks of age in mice not behaviorally tested. B) Total distance traveled (30 min). ANOVA, p = 0.001. C) Distance traveled over the course of the test (5 min bins). 2-way RM ANOVA; time: p = 0.003, immune status: p = 0.001, interaction: ns. D and E) Time in the center of the arena showed no significant difference in anxiety-like behavior. Tukey post hoc test for all analyses. WT: n = 6, Rag2−/−: n = 7, Recon: n = 8. * p≤ 0.05, ** p ≤ 0.01.