title: Granzyme A produced by γ(9)δ(2) T cells induces human macrophages to inhibit growth of an intracellular pathogen.
abstract: Human γ(9)δ(2) T cells potently inhibit pathogenic microbes, including intracellular mycobacteria, but the key inhibitory mechanism(s) involved have not been identified. We report a novel mechanism involving the inhibition of intracellular mycobacteria by soluble granzyme A. γ(9)δ(2) T cells produced soluble factors that could pass through 0.45 µm membranes and inhibit intracellular mycobacteria in human monocytes cultured below transwell inserts. Neutralization of TNF-α in co-cultures of infected monocytes and γ(9)δ(2) T cells prevented inhibition, suggesting that TNF-α was the critical inhibitory factor produced by γ(9)δ(2) T cells. However, only siRNA- mediated knockdown of TNF-α in infected monocytes, but not in γ(9)δ(2) T cells, prevented mycobacterial growth inhibition. Investigations of other soluble factors produced by γ(9)δ(2) T cells identified a highly significant correlation between the levels of granzyme A produced and intracellular mycobacterial growth inhibition. Furthermore, purified granzyme A alone induced inhibition of intracellular mycobacteria, while knockdown of granzyme A in γ(9)δ(2) T cell clones blocked their inhibitory effects. The inhibitory mechanism was independent of autophagy, apoptosis, nitric oxide production, type I interferons, Fas/FasL and perforin. These results demonstrate a novel microbial defense mechanism involving granzyme A-mediated triggering of TNF-α production by monocytes leading to intracellular mycobacterial growth suppression. This pathway may provide a protective mechanism relevant for the development of new vaccines and/or immunotherapies for macrophage-resident chronic microbial infections.
authors: Division of Infectious Diseases, Allergy and Immunology, Department of Internal Medicine, Saint Louis University, St. Louis, Missouri, USA.
authors: Charles T
authors: CT
authors: Spencer
authors: Getahun
authors: G
authors: Abate
authors: Isaac G
authors: IG
authors: Sakala
authors: Mei
authors: M
authors: Xia
authors: Steven M
authors: SM
authors: Truscott
authors: Christopher S
authors: CS
authors: Eickhoff
authors: Rebecca
authors: R
authors: Linn
authors: Azra
authors: A
authors: Blazevic
authors: Sunil S
authors: SS
authors: Metkar
authors: Guangyong
authors: G
authors: Peng
authors: Christopher J
authors: CJ
authors: Froelich
authors: Daniel F
authors: DF
authors: Hoft
mesh_terms: D002478:Cells, Cultured; D015964:Gene Expression Regulation, Bacterial; D055785:Gene Knockdown Techniques; D053804:Granzymes / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D054884:Host-Pathogen Interactions; D006801:Humans; D008264:Macrophages / Q000201:enzymology* / Q000276:immunology / Q000382:microbiology; D009000:Monocytes / Q000201:enzymology* / Q000276:immunology / Q000382:microbiology; D009161:Mycobacterium / Q000187:drug effects / Q000502:physiology*; D009500:Neutralization Tests; D034741:RNA, Small Interfering / Q000235:genetics; D016692:Receptors, Antigen, T-Cell, gamma-delta / Q000276:immunology / Q000378:metabolism; D016176:T-Lymphocyte Subsets / Q000201:enzymology* / Q000276:immunology / Q000382:microbiology; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D034741:RNA, Small Interfering; D016692:Receptors, Antigen, T-Cell, gamma-delta; D014409:Tumor Necrosis Factor-alpha; D053804:Granzymes