A significant increase in the percentage of epithelial cells staining TGF-β1+ in the lungs of BALB/c mice, but not CBA/Ca mice was observed between 0 and 6 hours p.i. Interestingly, the percentage of TGF-β1+ epithelial cells in BALB/c lungs returned to pre-infection levels by 12 hours p.i., perhaps as the result of cleavage of active TGF-β protein from the surface of the cells. Here, TGFB1 is linked to infection.