Microscopy images reveal how B cells are activated

Researchers at Sydney's Garvan Institute of Medical Research and the University of California San Francisco have captured microscopy images that reveal some important new details of how the immune system works.

The researchers were interested in knowing what drives the immune system's B cell activation and where it occurs. B cells produce antibodies in response to a specific invaders’ antigens. These antibodies help fight the invader at that time as well as in the future. Scientists have not understood how these B cells get exposed to the invader’s antigens if macrophages and dendritic cells are constantly destroying the invaders.

The researchers studied these immune interactions in a living mouse’s lymph nodes--where invaders are brought to be destroyed by macrophages and dendritic cells. Intravital and multiphoton microscopy images revealed highly specialized 'subcapsular sinus (SCS) macrophages' embedded in the lining of the lymph nodes’ sinus. The images showed the heads of these macrophages capturing the antigen on one side of the lining and their tails delivering it to B cells on the other side of the lining. In other words, the intact antigen passes through the subcapsular sinus almost like it is on a conveyer belt. 

This finding helps to clarify other groups’ observations of unusual macrophages in the subcapsular sinus and B cells residing nearby, and it clarifies how and where the B cells become activated. View videos of findings are here.

Research paper: Tri Giang Phan, Jesse A Green, Elizabeth E Gray, Ying Xu & Jason G Cyster, Nature Immunology, Immune complex relay by subcapsular sinus macrophages and noncognate B cells drives antibody affinity maturation. Published online: June 7, 2009, doi:10.1038/ni.1745.

Image courtesy of the U.S. National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Program.