SFTPA2 and infection: 3) In response to infection plus methacholine: a) the SP-A2 (1A3) gene variant exhibited higher lung function compared to SP-A2 (1A0), except for Crs for either sex; b) the SP-A1 (6A2, 6A4) gene variants exhibited diverse changes in lung function in the parameters studied for both sexes; c) the single gene products exhibited significantly increased lung function mechanics compared to co-ex.