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