The Role of Cytokines in T Help Responses to Viruses

T lymphocyte helper (Th) responses start from the activation of naive Th0 cells that get polarized towards Th1, Th2, Treg and Th17. Such polarization is achieved by delivering activation stimuli to naive T cells in the presence of given cytokines and by triggering certain receptors rather than others; indeed, the cytokine conditioning environment where cells get their activation signal is considered pivotal in determining the quality of the T cell response, and viruses seem to exert at least part of their influence on the antiviral response through cytokines. Indeed, the direction of polarization, and immune reactivity in general, have long been known to be influenced by viral infections. Because dendritic cells (DCs) not only start a response by Th0 but are also in charge of polarizing the Th immune response, they are also key determinants of the pathogenetic outcome of viral infection.