Transendothelial migration of human B cells: chemokine versus antigen
B cells, like T cells, can infiltrate sites of inflammation, but the processes and B cell subsets involved are poorly understood. Using human cells and in vitro assays, we find only a very small number of B cells will adhere to TNF-activated (but not to resting) human microvascular endothelial cells (ECs) under conditions of venular flow and do so by binding to ICAM-1 and VCAM-1. CXCL13 and to a lesser extent CXCL10 bound to the ECs can increase adhesion and induce transendothelial migration (TEM) of adherent naïve and memory B cells in 10-15 minutes through a process involving cell spreading, translocation of the microtubule organizing center (MTOC) into a trailing uropod and interacting with EC ALCAM. Engagement of the BCR by EC-bound anti-? light chain antibody also increases adhesion and TEM of ?+ but not ?+ B cells. BCR-induced TEM takes 30-60 minutes, requires Syk activation, is initiated by B cell rounding up and translocation of the MTOC to the region of the B cell adjacent to the EC and also utilizes EC ALCAM for TEM. BCR engagement reduces the number of B cells responding to chemokines and preferentially stimulates TEM of CD27+ B cells that co-express IgD, with or without IgM, as well as CD43.  RNA Seq analysis suggests peripheral blood CD19+CD27+CD43+IgD+ cells have increased expression of genes that support BCR activation as well as innate immune properties in comparison to total peripheral blood CD19+ cells. Overall design: To further characterize a rare population of human peripheral blood CD19+CD27+CD43+IgD+ cells, we prepared RNA from total CD19+ cells and isolated CD19+CD27+CD43+IgD+ cellsand compared their transcriptional profiles by RNA Seq.