Regulation of extravascular collectins in normal and injured tissue. In normal tissue (left), collectins are largely confined to luminal compartments such as the alveolar space (SP-D), or they are mostly present in the blood (MBL). In the case of SP-D, under normal conditions, alveolar macrophages govern the levels of this collectin through internalization by an unknown mechanism. After injury, disruption of normal tissue architecture leads to breakage of luminal tissue barriers and to extravasation of collectins into the extravascular space (right). Under these conditions, fibroblasts play a crucial role in regulating collectins by undertaking collectin endocytosis alongside tissue macrophages. The endocytosis of collectins by fibroblasts is mediated by the collagen receptor uPARAP (middle).