what structures and cells in the lower respiratory system would help fight and prevent infection

IgG opsonizing antibodies, specifically promoting & enhancing the phagocytic activity of alveolar macrophages, have been traditionally considered to be the main factor of the immunity of lower airways.

Nonspecific physical barriers include cough, reflex bronchoconstriction, angulation of the airways that favor impaction & subsequent elimination, & finally the mucociliary escalator.

Immune defenses found in the lower airways will include bronchus-associated lymphoid tissue, phagocytosis by PMN cells & macrophages, Immunoglobulin A & G, cytokines, surfactant, & cell-mediated immunity by T-lymphocytes.