miR-19b and miR-17 enhance DTH responses in vivo. (A) WT and KO mice were immunized subcutaneously with 100μg of KLH in CFA (Sigma-Aldrich) and 8 days later, were injected with 50μg of KLH in 1 footpad and PBS in the contralateral footpad. Increase in footpad thickness was measured for both groups at 48 hours after secondary challenge (n = 4). (B-E) WT B.10A mice were transferred through the tail vein with 0.5 × 10⁶ CD4⁺ T cells from 5C.C7 Rag2^−/− mice infected with GFP-, miR-17-, or miR-19b–expressing retrovirus and immunized subcutaneously with 20 μg of MCC peptide in CFA. Five days after immunization, mice were injected with 20 μg of MCC and PBS in each lateral footpad. Seventy-two hours later, the swelling of footpads (in panel B) and the number of total lymphocytes from the popliteal LN (in panel C) were measured (n ≥ 5). The percentage of IFN-γ–producing cells within the GFP⁺CD4⁺ population in the DLN was assayed (in panel D) by intracellular staining (n ≥ 4). Representative images of footpad tissues with H&E staining were shown in panel E. *P < .05; **P < .01; ***P < .001; and ns, no significance. Each experiment was repeated 3 times.