Smoking Effects

The strong association between smoking and squamous cell carcinoma of the head and neck is well established.51 Smoking induces changes to the respiratory epithelium and immune system, which ultimately puts patients at increased risk of developing respiratory infections.  Some of the changes that occur at the epithelial level include cell transformation, respiratory barrier disruption, mucous production, and transport alterations.52 Squamous metaplasia occurs throughout the respiratory tract with an increase in inflammatory cells and polymorphonuclear leukocytes.52Respiratory epithelium is normally quite impermeable due to tight cell-to-cell junctions; however, these are disrupted by smoke and leads to an increase in lung permeability.52 Additionally, smoking alters respiratory secretions and transport by increasing the volume of mucous while also slowing mucociliary clearance in the upper and lower respiratory pathways.52
Smoking also alters cellular and humoral immune responses. In heavy smokers, CD4 T cell populations are decreased while CD8 cells are increased.53 CD4 cells play a role in stimulating other immune cells including macrophages, B cells, and immunoglobulins; therefore, lower numbers of CD4 cells in smokers may increase their susceptibility to pulmonary infections.53Additionally, smokers have been found to have decreased neutrophil function, increased immunosuppressive effects of macrophages, and decreased proinflammatory cytokines.53 In the humoral immune system, immunoglobulin populations of IgA, IgG, and IgM have all been found to be lower than nonsmokers, thus predisposing to infection.53