The human polyomavirus, JCV, causes the fatal demyelinating disease progressive multifocal leukoencephalopathy in immunocompromised patients. We found that the serotonergic receptor 5HT2AR could act as the cellular receptor for JCV on human glial cells. The 5HT2A receptor antagonists inhibited JCV infection, and monoclonal antibodies directed at 5HT2A receptors blocked infection of glial cells by JCV, but not by SV40. Transfection of 5HT2A receptor-negative HeLa cells with a 5HT2A receptor rescued virus infection, and this infection was blocked by antibody to the 5HT2A receptor. A tagged 5HT2A receptor colocalized with labeled JCV in an endosomal compartment following internalization. Serotonin receptor antagonists may thus be useful in the treatment of progressive multifocal leukoencephalopathy.

Integrin-mediated cell migration is central to many biologic and pathologic processes. During inflammation, tissue injury results from excessive infiltration and sequestration of activated leukocytes. Recombinant human activated protein C (rhAPC) has been shown to protect patients with severe sepsis, although the mechanism underlying this protective effect remains unclear. Here, we show that rhAPC directly binds to ␤ 1 and ␤ 3 integrins and inhibits neutrophil migration, both in vitro and in vivo. We found that human APC possesses an Arg-Gly-Asp (RGD) sequence, which is critical for the inhibition. Mutation of this sequence abolished both integrin binding and inhibition of neutrophil migration. In addition, treatment of septic mice with a RGD peptide recapitulated the beneficial effects of rhAPC on survival. Thus, we conclude that leukocyte integrins are novel cellular receptors for rhAPC and the interaction decreases neutrophil recruitment into tissues, providing a potential mechanism by which rhAPC may protect against sepsis. IntroductionMigration of leukocytes to infection sites is vital for pathogen clearance and, thus, host survival. 1 Interaction of cell surface integrins with their counterpart ligands, which are expressed on the endothelial surface, results in the localization and adherence of circulating neutrophils to endothelial cells. This is followed by neutrophil activation and directed migration to sites of infection through the extracellular matrix. An important function of integrins is to concentrate neutrophils at the infection site, ensuring that their immune products and activities remain at this site, while minimizing unnecessary injury to uninfected tissues. Sustained or dysregulated integrin activation, resulting in abnormal neutrophil trafficking, as well as direct damage to the vasculature and the underlying tissue, is known to contribute to sepsis. [2][3][4] Recombinant human activated protein C (rhAPC), the only FDA-approved drug for treating severe sepsis, is a vitamin K-dependent serine protease that is derived from protein C (PC). Activated protein C (APC) is most well known for its anticoagulant functions. Although initial hypotheses to explain its efficacy in preventing severe sepsis centered on the antithrombotic and profibrinolytic functions of rhAPC, 5-8 other agents including antithrombin III and tissue-factor pathway inhibitor, known to have potent effects on such pathways, did not demonstrate the same clinical efficacy in the treatment of severe sepsis as rhAPC, 9,10 suggesting the ability of APC to improve several immunerelated functions independent of its anticoagulant functions. Although regulation of leukocyte migration has been proposed to underlie the protective effects of APC against sepsis, 11-16 the molecular mechanisms of the inhibitory effects of APC have not been demonstrated. Methods ReagentsRecombinant human APC (rhAPC) was obtained from Eli Lilly (Indianapolis, IN). The protein C mutant containing Glu substitution in place of Asp-222 (D222E) was constructed by...