Are T lymphocytes also innate immune cells?
Recently, a series of studies from Prof. Tang Hong's lab indicate that innate-like T lymphocytes play a pivotal role in the maintenance of homeostasis of innate inflammatory responses.
In sterile inflammation such as acute cardiac inflammatory response to high blood pressure, vascular endothelial cells and fibroblasts derived IFN-γ is responsible for recruitment and activation of CD8+ T cells. This process is required to initiate and augment macrophage-mediated inflammation.Furthermore,CD8+ T cells recruit and activate macrophage rely on direct cell-cell contact, whereas in a specific antigen or TCR independent manner. CD8+ T cells possess conserved characteristics of innate immune cells, if the time frame of response and antigen nonspecidicity are considered. The innate-like property of T cells is also well illustrated in inflammation caused by infection. TangHong lab previous studies indicate that naive CD4+ and CD8+ T cells dampen innate immune response during early phases of pathogen infection. Consistent with the situation in sterile inflammation, T cells participate in regulating innate immune response caused by infection needs cell-cell contact, yet depends on antigen specifity or TCR engagement.In conclusion,T cells posses evolutionally conserved characteristics of innate immune cells, and probably belong to the innate immune system, since its unique role in the regulation of early acute phase of inflammation.