(271g) Migration Against the Direction of Flow Is LFA-1 Dependent in Human Hematopoietic Stem and Progenitor Cells

The recruitment of immune cells during inflammation is regulated by a multi-step, leukocyte adhesion cascade of cell rolling, activation, adhesion, and transmigration through the endothelial barrier. Similarly, Hematopoietic Stem and Progenitor Cells (HSPCs) use this pathway to migrate and home to the bone marrow in order to restart hematopoiesis post-transplantation. After selectin-mediated braking and slow rolling, HSPCs migrate along the vascular endothelium on a variety of adhesion ligands including Intracellular Adhesion Molecule-1 (ICAM-1), Vascular Cell Adhesion Molecule-1 (VCAM-1) or Mucosal Addressin Cellular Adhesion Molecule-1 (MAdCAM-1). Previous work by ourselves (1) and others (2) has demonstrated an interesting phenomena where both murine and human T lymphocytes, which have a remarkably similar integrin profile as HSPCs, can migrate efficiently upstream (against the direction of shear-flow) on ICAM-1 surfaces while migrating downstream (with the direction of shear flow) on VCAM-1. Other immune cell types, such as neutrophils, do not show this behavior.

Here we describe for the first time how both the KG1a immortalized stem cell line and primary bone marrow CD34⁺ HSPCs can migrate against the direction of fluid flow on surfaces coated with cell adhesion molecules (CAMs). Using a laminar flow chamber, we demonstrate that KG1a cells and primary HSPCs migrate upstream on ICAM-1, downstream on VCAM-1, and both upstream and downstream on MAdCAM-1. Also, we demonstrate that KG1a cells and HSPCs display upstream migration on mixed surfaces of multiple CAMs and surfaces containing both E-selectin and CAMs, much like the activated endothelial surface. Furthermore, both KG1a and Primary HSPCs migrate upstream on activated HUVEC monolayers at shear rates seen in the vasculature. Blocking with monoclonal antibodies, we show that Lymphocyte Function-associated Antigen-1 (LFA-1) is the sole cell-borne integrin responsible for upstream migration along the endothelium. Signaling events downstream of LFA-1 (α_Lβ₂) engagement are critical to this mode of motility and furthermore, the localization of activated LFA-1 and the F-actin network are fundamentally different during upstream as compared to downstream migration. In all, this upstream motility has direct implications in understanding of how HSPCs traffic during bone marrow transplants and holds potential in having HSPCs better home to the marrow.

REFERENCES:

1. Dominguez GA, Anderson NR, & Hammer DA (2015) The direction of migration of T-lymphocytes under flow depends upon which adhesion receptors are engaged(). Integrative biology : quantitative biosciences from nano to macro 7(3):345-355.

2. Valignat M-P, Theodoly O, Gucciardi A, Hogg N, & Lellouch Annemarie C (2013) T Lymphocytes Orient against the Direction of Fluid Flow during LFA-1-Mediated Migration. Biophysical Journal 104(2):322-331.