Lack of Th17 Cell Generation in Patients with Severe Burn Injuries

Severe burn patients are immunodeficient and highly susceptible to infection of Candida albicans, a fungus that causes an opportunistic infection of the skin and mucosal membranes. Fungal infections can be attributed to 33% of mortality among patients with total body surface area (TBSA) burns. Above all, C.albicans infection results in the highest percentage of TBSA patient deaths [1].

Resistance against C.albicans infection is largely attributed to the anti-fungal activities of IL-17 producing CD4 T cells, or Th17 cells. Upon activation, CD4 T cells differentiate into three subsets of T helper cells; Th1, Th2, and Th17. Each type of Th cell produces a unique collection of cytokines, or chemical messengers, which activate different varieties of immune responses [2]. Th17 cells predominantly secrete IL-17, which is essential for mediating host defenses in mucosal surfaces such as the lungs and gut. Past research has implicated IL-17 in the regulation of neutrophils, which are leukocytes involved in the rapid responses of the innate immunity [3]. Specifically, IL-17 recruits neutrophils to a site of infection and enhances the function of epithelial cells, endothelial cells, and macrophages to produces pro-inflammatory cytokines [1]. Previous research implicates IL-17 deficiency in C.albicans infection and chronic mucocutaneous candidasis and demonstrates the necessity of IL-17 to combat fungal infections.

In the present study Inatsu and colleagues attempt to generate Th17 cell cultures in the presence of severely burned patient PBMC (peripheral blood mononuclear cells). PBMC are blood cells with a round nucleus such as monocytes and macrophages [4]. Prior to culture, patient’s PBMC were stimulated by C.albicans antigen (CAg), a protein derived from the fungus that can bind to a cell surface receptor and result in lymphocyte activation. The rationale was that CAg activated cells will be stimulated to produce Th17 cells and IL-17. Ultimately, Th17 were not detected in the cell cultures of CAg activated PBMC. Inatsu and colleagues hypothesis that IL-10, a cytokine detected in the sample of burn patient PBMC, inhibits the generation of Th17 cells and contributes to the increased susceptibility of TBSA individuals to C.albicans.

A variety of experiments were conducted to examine the production of IL-17 in burn patients and healthy participants. First, PBMC from three burn patients and three healthy donors were activated by CAg for a total of five days. IL-17 was not produced by the PBMC of the burn patients; conversely, healthy donor PBMC produced IL-17, which peaked in concentration on day 3. An additional test of 26 burn patients and 5 healthy individuals revealed that burn patients did not produce a statistically significant amount of IL-17 after stimulation with CAg. Culture assays revealed a slightly elevated level of IL-17 production in the samples of acute-phase burn patients, but did not reveal IL-17 in the assay of chronic-phase burn patients. Acute-phase is the shock phase, characterized by a depressed cardiac output and metabolic rate; whereas, the chronic-phase is a prolonged period characterized by elevated cardiac and metabolic rate [5]. There were no significant levels of IL-17 production despite the slight elevation of cytokine in acute-phase patients.

In subsequent experiments, flow cytometry was utilized to analyze CAg stimulated PBMC cultures for the presence of IL-17+ CD4+cells, or Th17 cells. The results indicated that the burn patients did not produce significantly increase levels of Th17 cells. Conversely, healthy individuals experienced a nine-fold increase in Th17 cell production in the presence of CAg.

Following experiments examined the effect of burn patient sera on the inhibition of Th17 activity. Serum is blood fluid that does not contain clotting factors [6]. First, PBMC from healthy donors were cultured in a medium of CAg and burn patient sera. Following cultivation, Inatsu and colleagues determined the ability of the PBMC to produce IL-17. Ultimately, IL-17 production was reduced in these individuals when compared to the levels of IL-17 produced when PBMC were cultured exclusively in CAg. Additionally, flow cytometry revealed that Th17 cell production was also decreased in healthy cells cultured in burn patient sera.

Previous research concludes that IL-10, an immunosuppressive cytokine, is present in the blood sera of burn patients. Inatsu and colleagues hypothesize that IL-10 dampens the immune response in burn patients and prevents the proliferation of Th17 cells and the production of IL-17. To test this hypothesis the researchers examined the concentrations of IL-17 produced by healthy donor PMBC cultured in CAg and IL-10. Ultimately, assay analysis and flow cytometry revealed that healthy donor cells did not produce IL-17 or Th17 cells. The results confirmed the hypothesis that IL-10 in the blood of burn patients inhibits a Th17 response and prevents the production of IL-17.

Inatsu and colleagues fail to propose an explanation for the inhibition of a Th17 response burn patients. However they do suggest that TBSA patient immunity generally presents a bias towards a Th2 response. Th2 cell responses effectively combat extracellular pathogens and are initiates primarily in musocal tissue. Th2 favors a humoral response in which antibodies are produced to neutralize pathogens without damaging the surrounding host cells [7]. Th17 responses favor aggressive inflammatory processes that can harm the delicate tissue of the mucosa. Burn patients experience extreme damage to the skin and mucosal tissue and the immune system may bias an anti-fungal response away form an aggressive inflammatory response that can potentially amplify tissue damage.

The present research will enlighten future treatment of severe burn patients, specifically the treatment of opportunistic fungal infections. Inatsu and colleagues demonstrate that in order to improve the treatment of C.albicans in TBSA patients, doctors must address the IL-10 inhibition of the Th-17 response. Altering the concentration of IL-10 will allow for enhanced anti-fungal immunity that can combat C.albicans. Future research can further examine the inhibitory interactions between IL-10 and Th17 cells. It may be possible that there are other factors in the sera of burn patients that are contributing to an immune shift away from a Th17 response.

Primary Source

[1] Inatsu, A., Kogiso, M., Jeschke, M.G., Asai, A. (2011). Lack of Th17 Cell Generation in Patients with Severe Burn Injuries. The Journal of Immunology. 187: 2155-2161.

Other Sources

[2] Korn,T., Bettelli, E., KuchrooV.K.(2009). IL-17 and Th17 cells. Annual Immunology Review, 27: 485-517 http://www.ncbi.nlm.nih.gov/pubmed/19132915

[3] Conti, J.R., Shen, F., Nayyar, N., Stocum, E., Sun, J.N., Lindemann, M.J. (2009). Th17 cells and IL-17 receptor signaling are essential for mucosal host defense against oral candidiasis. The Journal of Experimental Medicine, 206: 299-311.

[4] Hatton, G., Oceana, S., Collart, D., Using the News Thermo Scientific Benchtop 1-liter Centrifuge. http://www.kendro.com/eThermo/CMA/PDFs/Various/File_52363.pdf

[5] Wolfe, R.R., Acute Versus Chronic Responses to Burn Injury (1981). The Journal of Immunology 8: 105-115. http://www.ncbi.nlm.nih.gov/pubmed/7016359

[6] Goncales, F.L., Periera, J.S., Silva, C., Thomaz, G.R., Pavan, M.H., (2003). Hepatitis B Virus DNA in Sera of Blood Donors and of Patients Infected with Hepatitis C Virus and Human Immunodeficiency Virus. Clinical and Diagnostic Laboratory Immunology. 10: 718-720. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC164243/

[7] Berger, A., Th1 and Th2 responses: What are they? (2000). British Medical Journal. 12: 424. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC27457/

[8] Chaudhry, A., Rudra, D., Treuting,P., Samstein, R., Liang, Y., Kas, A., (2009). Cd4 Regulatory T Cells Control Th17 Responses in a Stat3 Dependent Manner. Science. 326: 986-991. http://www.sciencemag.org/content/326/5955/986.full