Armed 'killer' cells can re-enter lymph nodes to destroy dendritic cells -- a specialized type of immune cell -- according to a report published online in Nature Immunology. Such killing by antigen-specific T cells reduces further priming of naive immune cells of similar specificity, thereby preventing excessive immune cell activation. The results overturn prevailing notions that lymph nodes provide restrictive environments that prevent entry of activated T cells.
Sallusto and colleagues show 'resting' lymph nodes continue to bar entry to previously activated immune 'killer' cells called effector memory CD8+ T cells. Upon inflammatory signals that occur during infection, however, lymph nodes are activated and transiently express a chemical signal called CXCL9 and recruits memory T cells directly from the bloodstream. These memory cells express a receptor called CXCR3 that recognizes CXCL9.
In addition to checking further immune activation, the CXCL9 entry pathway provides a means to combat pathogens, including viruses such as HIV that replicate in lymph node tissues. The study should also be instructive to those working toward more effective vaccine development and improving efficacy.
Federica Sallusto (Institute for Research in Biomedicine, Bellinzona, Switzerland)
Abstract available online.
(C) Nature Immunology press release.
Message posted by: Trevor M. D'Souza