Absence of IL-6 but not IL-11Rα in gp130Y757F/Y757F mice prevents lymphoid organ enlargement. Cellularity and mass of (A) thymus and (B) lymph nodes from gp130+/+, gp130Y757F/Y757F, gp130Y757F/Y757F:IL-6−/−, and gp130Y757F/Y757F:IL-11Rα1−/− mice. Data from 6 mice of each genotype are expressed as the mean ± SD. *P < .05 versus data from gp130+/+ mice.