Loss of Th17 is associated with CD4 T activation in 2009 H1N1 patients

Source: Jiang TJ, Zhang JY, Li WG, Xie YX, Zhang XW, Wang Y, Jin L, Wang FS, Zhao M.

Preferential loss of Th17 cells is associated with CD4 T cell activation in

patients with 2009 pandemic H1N1 swine-origin influenza A infection. Clin

Immunol. 2010 Dec;137(3):303-10. Epub 2010 Oct 12. PubMed PMID: 20943443.

 

H1N1 swine-origin influenza A virus (S-OIV) is a novel influenza H1N1 strain that first emerged in humans in Mexico during March 2009. The incubation period is 1-7 days. Past studies have reported that host immune response can be a critical factor in determining various outcomes of influenza infection. These studies have reported that while moderate increase in proinflammatory responses may favor viral clearance, hyper activated inflammatory response can have detrimental effects on the host. It has also been noted that after innate immunity activation there could be an abundance of virus induced inflammatory cytokines which can lead to subsequent antigen non-specific T cell activation in mice and human with viral infection.

Among the T cells, helper CD4+ T cells release a number of distinct cytokines. One such cytokine is IFN-gamma which is released by Th1 cells and which is conventionally thought to exacerbate tissue damage and control viral infection. Regulatory T cells (Tregs) are immunosuppressive and play an important role in the regulation of immune responses. In contrast, IL-17 producing CD4+ T cells (Th17) are known to play role in both chronic inflammation and in host defense against pathogens. Many studies have found that Th17 cells can play important role in protecting mice against influenza challenge. Studies have also observed Th1 and Th17 hypercytokinemia as early host response in severe pandemic influenza.

In authors' words, "whether the change of T helper subsets could bridge the inflammatory activation and T cell activation during host-pathogen interactions at an early stage of A/H1N1 infection has not been well defined".

Thus, in the present work, the authors tend to study peripheral T cells subsets in acute S-OIV-infected patients.

Study subjects: For this study, investigators collected blood samples from 53 confirmed S-OIV-infected patients and 21 healthy controls. The patients were divided into three groups according to the day of first clinical manifestation. These three groups included early stage group (Patients enrolled within 3 days after clinical onset of symptoms), intermediate stage group (patients enrolled between 4-7 days after onset) and late stage group (patients enrolled after 8 days).

RESULTS:

1. S-OIV infection results in generalized T cell depletion and T cell activation: Using flow cytometry the authors compared the absolute numbers of circulating CD3+, CD4+ and CD8+ T cells in 53 patients at the acute and convalescent stages of S-OIV infection. They observed that mean absolute CD3+, CD4+ and CD8+ T cell counts in healthy individuals were much higher than in patients. Among the three groups of patients, the patients in the early stage showed lowest counts and the counts progressively increased in intermediate and late stage patients. These data suggested that S-OIV infection leads to a rapid depletion of CD3+, CD4+ and CD8+ T cells at the early stage (1-3 days), followed by a rapid and significant restoration of CD3+, CD4+ and CD8+ T cells at 4 days after the onset of illness. Among the patients with early stage infection, T cell counts almost doubled in the convalescent phase. Among the intermediate stage patients, T cells counts were decreased at the convalescent stage and among the late stage patients no difference in T cell counts was observed in the convalescent phase. The authors also compared the expression of CD38 and HLA-DR on CD4+ and CD8+ T cells in different patient groups and healthy controls. They found that expression of CD38 and HLA-DR was higher in all CD4+ T cells than in healthy controls in early stage patients. Furthermore, they observed that expression of CD38 was upregulated in CD8+ T cells in early stage patients but there was no significant difference in HLA-DR expression on CD8+ T cells in early stage patients. The expression of CD38 and HLA-DR on CD4+ and CD8+ T cells gradually decreased in patients at the intermediate stage and late stage when compared to early stage patients. Interestingly, CD38 and HLA-DR expression were higher in convalescent stages among different groups.
   
2. Preferential loss of IL-17 expressing Th17 cells after S-OIV infection: The authors then compared the frequencies of Th1 (IFN-gamma producing CD4+ T cells), Th17 and Tregs in peripheral blood from healthy controls and patients and observed that the absolute T cell counts of Th1, Th17 and Tregs cells were significantly decreased in patients in comparison to controls. They also observed that percentage of Th1 cells was significantly increased in S-OIV infected patients in comparison to controls. They further observed that percentage of Th1 cells was more at the convalescent phase in early stage patients. All these data indicate that Th1 cells play important roles in viral clearance. In contrast to Th1 cells, the frequency of Th17 cells was significantly reduced in S-OIV infected patients in comparison to controls. However, the Th17 cells showed a gradual increase from early to late phase. Tregs did not show any significant difference in frequency among patients and controls. Thus, it can be derived that Th17 cells are more prone to be depleted at an early stage after S-OIV infection.
   
3. Th17 cells and CD4 depletion at early clinical onset is associated with sustained CD4 T cell immune activation: The authors next sought to determine the impact of depletion of Th17 cells and CD4 on T cell activation. They found that frequency of CD38+ T or HLA-DR+ T cells was negatively correlated with CD4 T cell counts or Th17 cell frequency. The authors did not observe any negative correlation with Th1 or Treg frequency. Taken together, all these data indicate that the CD4 depletion and selective loss of Th17 cells, not Th1 or Treg cells, were strongly associated with increased CD4+ T cell activation at the early stage of S-OIV infection.
   
4. S-OIV infection induced IFN-α constricts Th17 responses: The authors also analyzed the serum concentrations of IFN-α to examine its association with decrease of Th17 cells in virus infected patients. They found that serum IFN- α was highly upregulated in patients in comparison to controls. They also found that patients of early stage had lowest concentration of IL-17 among the three groups. To determine the effect of IFN- α on the production of IL-17 from Th17 cells in vitro, the authors treated PBMCs from healthy controls with IFN- α and looked for expression of IL-17 and IFN-λ. The experiment showed that IL-17 production from CD4+ T cells was significantly reduced in the presence of IFN- α. In contrast, the production of IFN-λ was significantly increased in the presence of IFN- α. These results indicate that S-OIV infection –induced IFN- α may partly constrict the function of Th17 cells.