CD4(+)CD25(+) T regulatory cells inhibit CD8(+) IFN-gamma production during acute and chronic FIV infection utilizing a membrane TGF-beta-dependent mechanism.
CD8(+) lymphocytes are critical to the control and elimination of viral pathogens. Impaired CD8(+) responses are well recognized in lentiviral infections; however, the mechanisms underlying CD8(+) impairment remain elusive. Using the feline immunodeficiency virus (FIV) model for human AIDS, we reported previously that CD4(+)CD25(+) Treg cells in both the acute and long-term, asymptomatic phase of infection are constitutively activated and suppress CD4(+)CD25(-) T cell responses. In the current study, we have demonstrated that CD4(+)CD25(+) Treg cells suppress CD8(+) responses to immune stimulation during both the acute and chronic, asymptomatic phase of FIV infection and that the mechanism of suppression may be mediated by membrane-associated TGF-beta (mTGF-beta) on CD4(+)CD25(+) lymphocytes. Depletion of CD4(+)CD25(+) lymphocytes from lymph node suspensions significantly enhanced production of IFN-gamma during the acute phase of infection and coculture of CD8(+) lymphocytes with CD4(+)CD25(+) lymphocytes resulted in suppression of CD8(+) IFN-gamma during both the acute and chronic stages of infection. FACS analysis indicated that there was TGF-betaRII upregulation on CD8(+) cells from FIV(+) cats during the acute and chronic stage of infection. In addition, there was upregulation of mTGF-beta on the CD4(+)CD25(+) subset in chronically infected cats. In support of activation of the TGF-beta signaling pathway, Western blotting showed Smad 2 phosphorylation in CD8(+) targets following CD4(+)CD25(+)/CD8(+) coculture. These results demonstrate the suppressive effect CD4(+)CD25(+) Treg cells have on the CD8(+) immune response during the acute and chronic stages of FIV infection and suggest that the mechanism of suppression may be mediated by mTGF-beta.
Department of Population Health and Pathobiology, North Carolina State University College of Veterinary Medicine , Raleigh, NC 27606, USA.
Jonathan E
JE
Fogle
Angela M
AM
Mexas
Wayne A
WA
Tompkins
Mary B
MB
Tompkins
D000818:Animals; D015704:CD4 Antigens / Q000032:analysis; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D002371:Cat Diseases / Q000276:immunology* / Q000821:virology; D002415:Cats; D007108:Immune Tolerance; D016089:Immunodeficiency Virus, Feline / Q000276:immunology*; D007371:Interferon-gamma / Q000037:antagonists & inhibitors*; D053645:Interleukin-2 Receptor alpha Subunit / Q000032:analysis; D016180:Lentivirus Infections / Q000662:veterinary* / Q000821:virology; D050378:T-Lymphocytes, Regulatory / Q000737:chemistry / Q000276:immunology*; D016212:Transforming Growth Factor beta / Q000276:immunology*
D015704:CD4 Antigens; D053645:Interleukin-2 Receptor alpha Subunit; D016212:Transforming Growth Factor beta; D007371:Interferon-gamma