T lymphocytes bearing the γδ T cell receptor are known to play an important role in the first-line defense against viral, bacterial and fungal pathogens. Two main subsets of γδ T cells are known, showing distinct functional behavior: Vδ2 T lymphocytes, circulating in the peripheral blood, are involved in the response to mycobacterial infections and certain viruses, including coxsackie virus B3 and herpes simplex virus type 2. Vδ1 T cells are resident in the mucosalassociated lymphoid tissue and are reported to participate in the immunity against Listeria monocytogenes and cytomegalovirus. Vδ2 T lymphocytes recognize non-peptidic phosphorylated metabolites of isoprenoid biosynthesis, expressed by mycobacteria, while Vδ1 T cells mainly interact with MHC-related antigens (MIC-A and MIC-B) and with receptors, called UL-16 binding proteins, for the UL-16 protein produced by cytomegalovirus-infected cells. Both Vδ1 and Vδ2 T cells can produce interferon-γ in response to MIC-A+ cells or non-peptide antigens, respectively. Moreover, production of TNF-α by human Vγ9/Vδ2 T cells has been demonstrated in response to bacterial products and non-peptidic molecules. Recently, it has been reported that γδ T lymphocytes can produce IL-17 during Escherichia coli or Mycobacterium tuberculosis infections in mice. This is of interest as IL-17 is emerging as a cytokine crucial in the control of intracellular pathogens and fungi. In this review, we will discuss the possible role of IL-17 producing γδ T cells in the regulation of acute and chronic inflammation, focusing on the different responses of the two subsets to mycobacterial, viral or fungal antigens.
Division of Immunology, Transplants and Infectious Diseases, San Raffaele Scientific Institute, Via Olgettina 60, 20132-Milan, Italy.
Publication date: December 1, 2009
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