The absence of IL-21R on hematopoietic cells is primarily responsible for impaired Th2 immune responses in the lung. Reconstituted bone marrow chimeras were immunized intraperitoneally with OVA adsorbed in alum adjuvant, followed 10 days later by intranasal challenge with OVA on 4 consecutive days. Two days after the final challenge, the number of CD4 T cells in (A) DLN and (B) BAL was determined by FACS analysis. (C) Eosinophils that had infiltrated into the airways were determined by differential counts. (D) The proportion of CD4⁺ T cells producing IL-4 and IFN-γ was determined after PMA/ionomycin restimulation by intracellular cytokine staining and FACS analysis. Column plots indicate averages ± SD of a representative experiment using 4 mice per group.