| Recent identification of the coxsackie B and adenovirus type 2 and 5 receptor (CAR), allows the molecular basis of adenoviral infection to be investigated. Human airway epithelia are resistant to adenovirus infection from the apical surface. Therefore, we investigated CAR in an in vitro model of human airway epithelia. Epithelia express CAR; however, the receptor polarized to the basolateral membrane. Virus efficiently infected epithelia from the basolateral surface because adenovirus fiber binds CAR. Moreover, CAR expressed on a GPI anchor localized to the apical membrane where it bound adenovirus and mediated infection. Thus, basolateral localization of CAR explains the inefficiency of adenovirus infection from the apical surface.; However, this observation suggests adenovirus may use a basolaterally localized receptor for other reasons. We found that progeny adenovirus initially released basolaterally, but then gains access to the apical/lumenal surface through a paracellular route. Moreover, adenovirus fiber binding to the cell adhesion molecule CAR was both necessary and sufficient to induce paracellular leak and allow the virus access to the apical surface and hence the environment. Thus adenovirus uses CAR to bind target cells, and to escape the epithelia.; In addition to viral pathogenesis, we also studied gene transfer as a treatment for cystic fibrosis. Adenovirus vectors are limited by problems of persistence, thus we investigated other candidates. Adeno-associated virus (AAV) vectors are capable of long-term gene expression. However, while AAV2-mediated gene transfer to muscle has partially replaced Factor IX deficiency in hemophilia patients, its ability to mediate gene transfer to the lungs for cystic fibrosis is hindered by lack of apical receptors. In contrast to AAV2, the apical membrane of epithelia contain high-affinity receptors for AAV5. Binding and gene transfer with AAV5 required 2,3-linked sialic acid suggesting it is a receptor for AAV5 or a necessary component of a receptor complex. Hence, AAV5 may have utility as a gene transfer vector in cystic fibrosis. Further elucidation of the receptor should enhance understanding of parvovirus biology and expand the therapeutic targets for AAV vectors. |
