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Endothelial CD99 supports arrest of mouse neutrophils in venules and binds to neutrophil PILRs

Debashree Goswami, Sigrid März, Yu-Tung Li, Annette Artz, Kerstin Schäfer, Ruth Seelige, Mariana Pacheco-Blanco, Ding Jing, Maria Gabriele Bixel, Masatake Araki, Kimi Araki, Ken-Ichi Yamamura and Dietmar Vestweber

Key Points

  • Only CD99 on endothelial cells, not on neutrophils, participates in neutrophil extravasation in vivo.

  • A new function was found for CD99: support of chemokine-induced β2-integrin activation and neutrophil arrest by binding to PILR.

Abstract

CD99 is a crucial regulator of the transmigration (diapedesis) of leukocytes through the blood vessel wall. Here, we report that CD99 acts at 2 different steps in the extravasation process. In agreement with previous antibody-blocking experiments, we found that CD99 gene inactivation caused neutrophil accumulation between venular endothelial cells and the basement membrane in the inflamed cremaster. Unexpectedly, we additionally found that leukocyte attachment to the luminal surface of the venular endothelium was impaired in the absence of CD99. Intravital video microscopy revealed that CD99 supported rapid chemokine-induced leukocyte arrest. Inhibition of leukocyte attachment and extravasation were both solely due to the absence of CD99 on endothelial cells, whereas CD99 on leukocytes was irrelevant. Therefore, we searched for heterophilic ligands of endothelial CD99 on neutrophils. We found that endothelial cells bind to the paired immunoglobulinlike receptors (PILRs) in a strictly CD99-dependent way. In addition, endothelial CD99 was coprecipitated with PILRs from neutrophils that adhered to endothelial cells. Furthermore, soluble CD99 carrying a transferable biotin tag could transfer this tag covalently to PILR when incubated with intact neutrophils. Binding of neutrophils under flow to a surface coated with P-selectin fragment crystallizable (Fc) and intercellular adhesion molecule 1 (ICAM-1) Fc became more shear resistant if CD99 Fc was coimmobilized. This increased shear resistance was lost if neutrophils were preincubated with anti-PILR antibodies. We concluded that endothelial CD99 promotes leukocyte attachment to endothelium in inflamed vessels by a heterophilic ligand. In addition, CD99 binds to PILRs on neutrophils, an interaction that leads to increased shear resistance of the neutrophil attachment to ICAM-1.

  • Submitted August 10, 2016.
  • Accepted February 14, 2017.
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