HOXA9−/− mice have small spleens and thymuses. Mean ± SE splenic and thymic weights in milligrams are shown for HOXA9−/− and 4 groups of control animals. (□) A9−/− (n = 39); () A9 +/− (n = 16); (▪) C57 (n = 39); (▧) 129 (n = 26); (▧) C57/129 (n = 27). *P < .01 for A9−/− versus all other groups.