PD-1H-Ig promotes airway inflammation in OVA-induced asthma. Allergic asthma was induced by OVA as described in Figure 1a. WT mice were i.v. injected with 20 μg PD-1H-Ig plasmid in 2 ml PBS through the tail vein on days −1, 4 and 11. Flag-Ig plasmid was used as the control. BALF was collected after the last OVA challenge and stained (a) for leukocyte counts (b). The scale bar in a represents 100 μm. *P<0.05 and ***P<0.001 (two-tailed student’s t-test). All values are expressed as means±s.e.m. N=8 per group. All experiments were repeated at least three times. BALF, bronchoalveolar lavage fluid; i.v., intravenously; OVA, ovalbumin; WT, wild-type.