The alpha2beta1 integrin: a novel collectin/C1q receptor

Our laboratory focuses on the alpha2beta1 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 alpha2beta1 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 alpha2beta1 integrin expression is widespread, it is not ubiquitous. Rather, it is expressed in a differentiation-dependent and activation-dependent manner. Interactions between the alpha2beta1 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 alpha2beta1 integrin during the immune response. Our laboratory generated an alpha2beta1 integrin-deficient mouse to define the role of the alpha2beta1 integrin in vivo. Our studies demonstrated that the alpha2-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 alpha2beta1 integrin, which include C1q and the collectins. The goal of this article is to review the important role that the interaction between the alpha2beta1 integrin and C1q plays in the innate immune response. The identification of C1q and the collectins as ligands for the alpha2beta1 integrin suggests that the integrin may play important roles in a number of immunological responses.