Host defense mechanism ◆ Upper-airway (nasal turbinates (2)mucocillary transport system: ciliary, mucus layer, IgA, mucosal pH, colonization of non-pathogenic bacteria ◆ Lower airway (1)glottis, cough, 2)innate immunity: macrophages, lysozymes, lactoferrin IgG, defensins, complement, cathelicidins, collectins ()epithelial barrier and antimicrobial peptide (4)specific host defense: T lymphocyte Upper- airway: (1)nasal turbinates, (2)mucocillary transport system: ciliary, mucus layer, sIgA, mucosal pH, colonization of non-pathogenic bacteria  Lower airway: (1)glottis, cough, (2)innate immunity: macrophages, lysozymes, lactoferrin, IgG, defensins, complement, cathelicidins, collectins (3)epithelial barrier and antimicrobial peptide (4)specific host defense: T lymphocyte