Practical and conceptual models of chronic obstructive pulmonary disease.

The challenges of chronic obstructive pulmonary disease and the difficulties in modeling its pathology in vitro and in vivo are substantial. Integration of innate- and adaptive-type responses with processes of scarring and healing do not fit comfortably with some definitions of the immune system, and, instead, this disease is an exemplar of a network-based system that we have named "contiguous immunity." The complicated and highly interconnected networks underpinning many biological processes show features of scale-free networks. Consideration of chronic obstructive pulmonary disease pathology as a scale-free network showing features of contiguous immunity might, in the future, aid identification and targeting of potential key "hubs"-these being principal components of the disease network-manipulation of which may yield successful new therapies.