New skills for old cells

Differentiation is usually a one-way street, and most cells that mature to fulfill a particular purpose will retain that function throughout their lives. This is not always the case, however, and new work from a team led by David Tarlinton and Stephen Nutt of the Walter and Eliza Hall Institute of Medical Research in Australia reveals a surprisingly flexible subset of immune cells¹.

Follicular helper T (T_FH) cells help promote the development of B cells, which secrete antibodies to destroy pathogens and other threats. Relatively little is known about how T_FH cells develop, and the researchers genetically engineered a mouse strain expressing a fluorescent marker that made these cells easier to track. Unexpectedly, they determined that T_FH cells continue to multiply in adult animals, a behavior typically not seen in fully differentiated cells. Immune system activation stimulated this proliferation, which eventually subsided as the immune response waned.

However, Nutt and Tarlinton observed that T_FH cells could become ‘memory T cells’. These recognize and respond rapidly to reappearance of the same immune trigger by giving rise both to various subpopulations of T_FH cells and ‘effector’ T cells, which amplify and direct the immune response. This suggests T_FH cells can play a more diverse role in immune function than previously anticipated.