Th2-like CD8 T cells: their role in protection against infectious diseases

The expression of cytolytic activity and production of interferon γ (IFN-γ) by CD8⁺ T cells is thought to play a fundamental role in protection against infection by viruses and intracellular parasites. François Erard and Graham Le Gros have recently shown that CD8⁺ T cells activated in the presence of interleukin 4 (IL-4) can switch development to a CD8⁻CD4⁻Th2-like phenotype that is not cytolytic and that does not produce IFN-γ. Here they speculate on whether this IL-4-induced switch is used by the host to make a more-effective response against parasite invasion, or i f it is a host mechanism used by the parasite to evade protective CD8⁺ T-cell responses.