Anti-retroviral therapy fails to restore the severe Th-17: Tc-17 imbalance observed in peripheral blood during simian immunodeficiency virus infection.
BACKGROUND
Human immuno deficiency virus and simian immunodeficiency virus infections are characterized by a severe loss of Th-17 cells (IL-17(+)CD4(+) T cells) that has been associated with disease progression and systemic dissemination of bacterial infections. Anti-retroviral therapy (ART) has led to repopulation of CD4(+) T cells in peripheral tissues with little sustainable repopulation in mucosal tissues. Given the central importance of Th-17 cells in mucosal homeostasis, it is not known if the failure of ART to permanently repopulate mucosal tissues is associated with a failure to restore Th-17 cells that are lost during infection.


METHODS
Dynamics of alpha4(+)beta7(hi) CD4(+) T cells in peripheral blood of SIV infected rhesus macaques were evaluated and compared to animals that were treated with ART. The frequency of Th-17 and Tc-17 cells was determined following infection and after therapy. Relative expression of IL-21, IL-23, and TGFbeta was determined using Taqman PCR.


RESULTS
Treatment of SIV infected rhesus macaques with anti-retroviral therapy was associated with a substantial repopulation of mucosal homing alpha4(+)beta7(hi)CD4(+) T cells in peripheral blood. This repopulation, however, was not accompanied by a restoration of Th-17 responses. Interestingly, SIV infection was associated with an increase in Tc-17 responses (IL-17(+)CD8(+) T cells) suggesting to a skewing in the ratio of Th-17: Tc-17 cells from a predominantly Th-17 phenotype to a predominantly Tc-17 phenotype. Surprisingly, Tc-17 responses remained high during the course of therapy suggesting that ART failed to correct the imbalance in Th-17 : Tc-17 responses induced following SIV infection.


CONCLUSIONS
ART was associated with substantial repopulation of alpha4(+)beta7(hi) CD4(+) T cells in peripheral blood with little or no rebound of Th-17 cells. On the other hand, repopulation of alpha4(+)beta7(hi) CD4(+) T cells was accompanied by persistence of high levels of Tc-17 cells in peripheral blood. The dysregulation of Th-17 and Tc-17 responses likely plays a role in disease progression.
Kader
M
M
Uniformed Services University of Health Sciences, Bethesda, MD 20814, USA.
Bixler
S
S
Piatak
M
M
Lifson
J
J
Mattapallil
J J
JJ
D000818:Animals; D044966:Anti-Retroviral Agents / Q000627:therapeutic use*; D016516:CD4-CD8 Ratio; D020381:Interleukin-17 / Q000378:metabolism*; D008253:Macaca mulatta; D016097:Simian Acquired Immunodeficiency Syndrome / Q000188:drug therapy* / Q000276:immunology; D015302:Simian Immunodeficiency Virus; D013602:T-Lymphocytes, Cytotoxic; D006377:T-Lymphocytes, Helper-Inducer; D019562:Viral Load
D044966:Anti-Retroviral Agents; D020381:Interleukin-17