Infection-fighting B cells go with the flow

Infection-fighting B cells go with the flow
B cell migration, tracked in these bone marrow images, was largely blocked after VCAM-1 was inhibited (right). Credit: Beck et al., 2014

Newly formed B cells take the easy way out when it comes to exiting the bone marrow, according to a study published in The Journal of Experimental Medicine.

For infection-fighting T and B to defend the body, they must first leave their birthplace—the thymus for T cells and for B cells. T cell migration within and eventual exit from the thymus are active processes governed by expression of specific (called GPCRs) that respond to external attractants and cause the cell to crawl toward exit sites. B cells are retained in the bone marrow by a similar mechanism controlled by a GPCR called CXCR4, which binds to a bone marrow-resident protein and also increases the expression of sticky "integrin" molecules, effectively tethering the cells in place.

But when it comes to leaving the bone marrow, B cells can afford to be lazy. João Pereira and colleagues at Yale University School of Medicine show that B cells actively migrate around the bone marrow with the help of CXCR4 and an integrin called VCAM-1. Without CXCR4, the cells slowed down and many stopped moving entirely, in part due to decreased expression of VCAM-1. For those cells near exit sites, decreased CXCR4 and VCAM-1 allowed them to be passively swept out of the bone marrow with the blood flow.

Why use different exit strategies in different organs is not completely clear. But the authors suggest that the go-with-the-flow strategy of the bone marrow may be due to its role in the production of , which do not express molecules required for active crawling.

The movement of bone marrow B cells was limited in the absence of VCAM-1, as shown in this time-lapse video. B cells (green) were tracked before (left) and after (right) treatment with anti-VCAM-1 antibodies. Credit: Beck et al., 2014

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More information: Beck, T.C., et al. 2014. J. Exp. Med. DOI: 10.1084/jem.20140457
Journal information: Journal of Experimental Medicine

Citation: Infection-fighting B cells go with the flow (2014, November 17) retrieved 15 October 2019 from https://medicalxpress.com/news/2014-11-infection-fighting-cells.html
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