Excessive proline synthesis caused by early respiratory virus infection combined with allergen sensitization contributed to allergic asthma in childhood. Mice were sensitized with PVM-OVA, PVM-OVA followed by BPTES or NFLP, or PVM-OVA followed by BPTES+Proline or NFLP+Proline, and challenged with OVA after 21 days post infection. (A) RI and Cdyn to methacholine (MCh, 6.25, 12.5, 25, and 50 mg/ml), (#, ▲, ◆P < 0.05, * *,##, ▲▲P < 0.01, * * *,###, ▲▲▲P < 0.001. PVM-OVA group compared to PBS group, *, or BPTES group, #, or NFLP group, ▲. BPTES group compared to BPTES +Pro group, ◆. NFLP group compared to NFLP +Pro group, ●). (B) H&E staining shows peribronchiolar, perivascular, and interstitial inflammatory cell infiltration. (100 X). (C) PAS staining shows bronchiolar mucus production (400X). (D, E) Scores for pulmonary inflammation or mucus. (F) Number of inflammatory cells in BALF. (G) Relative expression of IFN-γ, IL-17, IL-23 and MCP-1 by real-time PCR. Each experimental group contained three biology repeats. Data are presented as means standard deviations of five mice per group and are representative of two experiments. *P<0.05, **P<0.01, ***P<0.001, ****P<0.0001. ▲▲▲▲ means PVM-OVA group compared with NFLP group (P<0.0001).