CD40 and infection: Columnar LECs of the conducting airways (including club and multiciliated cells) have inducible MHC-II and constitutive expression of costimulators (CD40 and CD86, respectively), whereas the lamellar body-containing alveolar LECs (AT2 cells and SPClowMHChigh LECs) express constitutive MHC-II with PD-L1 (both of which increase during infection).