Human Lung Responses to Respiratory Pathogens

For most individuals, the lung has a remarkable ability to deal with exposure to a variety of
inhaled bacteria. Some individuals, however, do have recurrent bacterial infections, usually
in the form of acute or chronic bronchitis and, in some instances, pneumonia. The reasons for
this variability in bacterial infections between otherwise healthy subjects, between types of
lung disease, and within the same type of lung disease are poorly understood.

Variability in susceptibility to bacterial infections is partially explained by differences
in exposure to infectious agents, genetic susceptibility and innate (or early) immune
responses. It is of interest that the incidence and severity of bacterial infections is
greatest during the winter months. Other than viral infections, there are few variables that
change with season. Vitamin D is one known immune modulator with a seasonal periodicity. The
hypothesis of this study is that levels of vitamin D are an important determinant of the
innate defense of the lung against inhaled bacteria. The investigators further postulate that
vitamin D has effects on the innate immune function of both alveolar macrophages and lung
epithelial cells.