The α2β1 integrin: A novel collectin/C1q receptor

Our laboratory focuses on the α2β1 integrin, a receptor for a number of matrix and non-matrix ligands, including collagens, laminins, decorin, E-cadherin, matrix metalloproteinase-1 (MMP-1), endorepellin, and several viruses. The α2β1 integrin is expressed on numerous different cell types, including epithelial cells, endothelial cells, fibroblasts, and hematopoietic elements, including platelets and specific subsets of leukocytes. Although α2β1 integrin expression is widespread, it is not ubiquitous. Rather, it is expressed in a differentiation-dependent and activation-dependent manner. Interactions between the α2β1 integrin and extracellular matrix ligands have been implicated in important biological processes including inflammation and immunity. Studies from a number of laboratories have demonstrated a role for the α2β1 integrin during the immune response. Our laboratory generated an α2β1 integrin-deficient mouse to define the role of the α2β1 integrin in vivo. Our studies demonstrated that the α2-null mice have a profound defect in the innate immune response. We have recently reported the identification of a novel family of ligands for the α2β1 integrin, which include C1q and the collectins. The goal of this article is to review the important role that the interaction between the α2β1 integrin and C1q plays in the innate immune response. The identification of C1q and the collectins as ligands for the α2β1 integrin suggests that the integrin may play important roles in a number of immunological responses.