Dr. Brain's research emphasizes responses to inhaled gases, particulates, and microbes. His studies extend from the deposition of inhaled particles in the respiratory tract to their clearance by respiratory defense mechanisms. Of particular interest is the role of lung macrophages; this resident cell keeps lung surfaces clean and sterile. Moreover, the lung macrophage is also a critical regulator of inflammatory and immune responses. The context of these studies on macrophages is the prevention and pathogenesis of environmental lung disease as well as respiratory infection.
His research has utilized magnetic particles in macrophages throughout the body as a non-invasive tool for measuring cell motility and the response of macrophages to various mediators and toxins. Other experiments deal with the use of lung lavage to obtain and characterize macrophages. A rodent bioassay utilizing lung lavage has been developed; the assay has been used to estimate the relative toxicity of new and complex mixtures such as molds, urban dusts, welding fume, new materials being used in the workplace, as well as drugs and excipients administered by inhalation, including nanomaterials.
Respiratory infection is emphasized and includes mechanistic studies of the lung's defenses against Pseudomonas aeruginosa, an important pulmonary pathogen for patients with cystic fibrosis. Related studies deal with opportunistic lung infections in AIDS such as Pneumocystis carinii. Another area of study is drug delivery to and through the lungs, including inhaled insulin.