IL-4Rα expression is required for generation/maintenance of bystander memory CD8+ T cells in the periphery. (A–C) Combined spleen and lymph node lymphocytes from age-matched WT BALB/cByJ and IL-4Rα KO BALB/cByJ were analyzed for total lymphocyte count (A), frequency (B), and total number of CD8+ T cells (C). (D–F) As shown in D, CD8+ T cells were segregated into three populations based on CD44 and CXCR3 expression. The frequency (E) and number (F) of CD44lo CXCR3lo, CD44hi CXCR3lo, and CD44hi CXCR3hi CD8+ T cells was determined in WT and IL-4Rα KO BALB/cByJ mice. (G) Mixed BM chimeras were generated by introducing WT and IL-4Rα KO BALB/cByJ donor BM into lethally irradiated WT BALB/cByJ hosts. Chimeric mice were bled 8 wk later, and the frequency of CD8+ T cells with the indicated CD44/CXCR3 phenotype was determined for both donor populations. Error bars indicate mean ± SD. P-values are represented as *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001 by unpaired (A–C, E, and F) or paired (G) Student’s t test for BM chimeras. (A–C) Data are combined from two separate experiments (n = 9 for WT, n = 8 for IL-4Rα KO) and are representative of five experiments. (D–F) n = 4 for WT and n = 4 for IL-4Rα KO, and data are representative of five experiments. (G) n = 7 for mixed BM chimeras, and data are representative of three experiments.