IL-4-induced activation of the Stat6 pathway contributes to the suppression of cell-mediated immunity and death in sepsis.
BACKGROUND
Although studies have shown that there is a marked depression in cell-mediated (T(H)(1)) immunity after the onset of sepsis, the mechanism by which this occurs remains unknown. In this regard, the T(H2) cytokine IL-4 is known to regulate T(H1) and T(H2) cell responsiveness primarily through the activation of the signal transducer and activation of transcription factor-6 (Stat6) pathway.


METHODS
We hypothesized that IL-4 may contribute to the suppression of cell-mediated immunity and to death seen in sepsis and that IL-4 may be acting through the Stat6 pathway. To determine this, we induced cecal ligation and puncture (CLP) or sham-CLP in male BALB/c mice. Mice received 2 mg of monoclonal antibody against IL-4 or IgG control at 12 hours after CLP (ie, at the onset of immune suppression). Splenic T cells were then isolated 24 hours after CLP and stimulated with monoclonal antibody to CD3. Cytokine release and Stat6 phosphorylation (activation) were determined. In a separate group of animals, survival was assessed over 10 days.


RESULTS
The results indicate that after CLP, T cells are suppressed in their ability to release the T(H1) cytokines, IL-2 and IFN-gamma. Alternatively, the release of T(H2) cytokines IL-10 and IL-4 is markedly increased after CLP. This was associated with an increase in phosphorylated Stat6 protein. In vivo treatment of mice with monoclonal antibody to IL-4 at 12 hours after CLP restores T(H1) responsiveness while preventing the increase in T(H2) cytokine release and Stat6 phosphorylation. Furthermore, neutralization of IL-4 markedly increased the survival rates in septic animals.


CONCLUSIONS
Taken together, these data indicate that the T(H2) cytokine IL-4 contributes to the suppression of cell-mediated immunity and death associated with polymicrobial sepsis and suggest that IL-4 may be acting through the Stat6 pathway in septic animals.
Center for Surgical Research and Department of Surgery, Brown University School of Medicine and Rhode Island Hospital, Providence, 02903, USA.
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Song
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Chung
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Chaudry
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Ayala
D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D016207:Cytokines / Q000276:immunology*; D003643:Death; D007111:Immunity, Cellular; D007074:Immunoglobulin G / Q000494:pharmacology; D007371:Interferon-gamma / Q000276:immunology; D007376:Interleukin-2 / Q000276:immunology; D015847:Interleukin-4 / Q000276:immunology / Q000502:physiology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D010766:Phosphorylation; D050800:STAT6 Transcription Factor; D018805:Sepsis / Q000276:immunology*; D015398:Signal Transduction; D013154:Spleen / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*; D018417:Th1 Cells / Q000276:immunology; D015534:Trans-Activators / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D016207:Cytokines; D007074:Immunoglobulin G; D007376:Interleukin-2; D050800:STAT6 Transcription Factor; C494100:Stat6 protein, mouse; D015534:Trans-Activators; D015847:Interleukin-4; D007371:Interferon-gamma