( n of specific physical and chemical cue...)Chemical guidance of T cells leads to immunologic memory and long-term immunity

"Understanding the processes whereby CD8+ T cells find their way in the lymph nodes is important because their activation is essential for eliminating infected cells and for providing, together with antibodies, long-lasting protection following vaccinations," says NIAID Director Anthony S. Fauci, M.D.

The body contains hundreds of millions of CD8+ T cells, but only a tiny fraction of them become activated during an infection. These are selected because each CD8+ T cell carries a unique surface protein called a T-cell receptor, which recognizes only specific antigens (pieces of virus or bacteria that trigger the immune response). During an infection, CD8+ T cells that recognize antigens from the infecting pathogen are activated. These antigen-specific CD8+ T cells expand into a large population of active clones, which then sweep through the body, hunting down and killing infected cells.

For CD8+ T-cell activation to occur in the lymph node, the cell must encounter its target antigen--but that antigen must be displayed on the surface of another immune system cell, called a dendritic cell. Usually a third type of cell, known as a "helper" T cell, must be involved as well. But how do the CD8+ T cells find the right dendritic cells presenting the specific antigen they need to see? Moreover, how do they find the particular dendritic cells that have been properly stimulated by helper T cells?

Dr. Germain and his colleagues determined that naïve CD8+ T cells do not wander aimlessly through the lymph node but instead are steered towards areas in which dendritic cells concentrate. Think of the lymph node as a large airport terminal and the CD8+ T cells as the arriving passengers, says Dr. Germain. If passengers know that limo
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Source:NIH/National Institute of Allergy and Infectious Diseases