Of interest, SP-A content in SP-A1 and SP-A2 male mice in response to a single insult (infection) is the same, but in response to a double insult (infection and ozone exposure) the SP-A content in the SP-A2 mice is significantly higher (p < 0.05) than that in SP-A1 mice (Figure 5A). Here, TFF2 is linked to infection.