New Research Expands Understanding of IL17/IL22 in Oral Mucosal Immunity

The Division of Rheumatology and Clinical Immunology at UPMC and the University of Pittsburgh School of Medicine boasts of a distinguished array of research accomplishments in the field of cytokine functionality and their relationship to immunity and autoimmunity. The Gaffen Laboratory, led by professor of medicine and Gerald P. Rodnan Endowed Chair, Sarah L. Gaffen, PhD, has made seminal contributions in the understanding of the molecular mechanisms and signaling pathways of the IL-17 family of cytokines and their role in immunity, particularly of the oral mucosa and mucosal fungal infection, but also in understanding the physiological impact of cytokine blockade in humans.

In June 2020, a research team from the Gaffen Laboratory, led by Felix E.Y. Aggor, PhD, published significant new findings expanding the evidence for how interleukin-17 (IL-17) and the cytokine interleukin-22 (IL-22) drive immunity processes of the oral epithelial cells in relationship to fungal infection by Candida albicans. Dr. Aggor and his colleague’s paper, published in the journal Science Immunology, uncovered a novel relationship between IL-17 and IL-22 and is leading to new avenues of investigation for Dr. Aggor to pursue.

Summary of Key Findings and Implications

While much is known about how IL-17 functions and its role in various infectious immunity and autoimmunity processes, much less is known about the cytokine IL-22 – how it functions and how it interacts with other proteins and cells. Dr. Aggor’s research clarifies several aspects of IL-22 function and its interaction with IL-17 in the context of oral mucosal immunity

To begin, the research team shows that IL-17 and IL-22 carry out their functions and back-and-forth signaling in two distinct cellular layers of the oral mucosa. Previous research by the Gaffen laboratory and others established that the IL-17 receptor (IL-17R) functions within the suprabasal epithelial layer (SEL), and that IL-17 is crucial for driving protection against fungal infections.

“From prior research, we also knew that other cytokines could play a role in antifungal immunity, with IL-22 being one of the candidates,” says Dr. Aggor. “However, there was much less known about IL-22 in the context of oral candidiasis or oral thrush. I hypothesized that IL-22 could be acting on cellular types that respond to IL-17, such that IL-22 carried out its role in the suprabasal epithelium to protect against oral candidiasis. Interestingly, though, in our models, when we deleted the IL-22 receptor (IL-22R) in the SEL, it was clear that this deletion did not affect antifungal immunity.”

Taking a step back in the research, Dr. Aggor performed additional analysis using immunofluorescent staining and discovered that the IL-22 receptor had a different localization pattern in the oral mucosa compared to the IL-17 receptor. As it turns out, the IL-22 receptor is in the suprabasal layer alongside IL-17R, but it also is found in the underlying basal epithelial layer (BEL).

"With this finding, our team performed additional experiments deleting the IL-22 receptor from the basal epithelium, and this time our models showed definite impairment of their antifungal immunity capabilities, which clearly indicated to us that the IL-22 receptor, unlike the IL-17 receptor, was required in the basal epithelium for antifungal immunity," says Dr. Aggor. 

Prior research in other settings have shown that the cytokine IL-22 is one of the cytokines that activates the transcription factor known as STAT3. Dr. Aggor’s hypothesis, then, was that IL-22 could be driving antifungal protection in the oral mucosa through STAT3 activation.

"Further work by our team confirmed that STAT3 is activated in the basal epithelium, the same layer in which we found IL-22R. At this point, we created a model that knocked out the STAT3 gene in the basal epithelium. These models showed increased susceptibility to oral fungal infection," says Dr. Aggor. "Now, it had been previously established that STAT3 has a role in oral thrush. STAT3 has been implicated in the generation of Th17 cells. It is these immune cells that produce both IL-17 and IL-22. In individuals with a genetic or functional mutation in STAT3, we know that these individuals are incapable of generating Th17 cells and have compromised immunity to fungal infections. The role of STAT3 in the epithelium – in antifungal immunity – was not previously demonstrated. Our research was the first to show STAT3 may not only be needed in the generation of Th17 cells but also is important for the processes in the responding epithelial cells of the oral mucosa to drive antifungal immunity.”

Through additional mechanistic studies and gene expression analysis, Dr. Aggor’s team narrowed down the processes by which IL-22 can protect against oral candidiasis. His research found that in the oral mucosa, IL-22 drives the proliferation of cells in the basal epithelium. In turn, these cells give rise to the suprabasal epithelial cells, the cells in which the IL-17 receptor is expressed. The mechanism at work during oral antifungal immune response is such that the damaged or infected suprabasal epithelial cells get sloughed off and then are replenished. With the absence of IL-22R, those cells in the basal epithelium cannot proliferate effectively to replenish the cells lost during the infection process, thereby leading to propagation or maintenance of the fungal infection.

“To summarize, the key findings from our research show that the two layers of the oral epithelium work in conjunction to drive protection against oral candidiasis – the suprabasal layer, which expresses the IL-17 receptor, and the basal epithelial layer, which expresses the IL-22 receptor. Both of these signals are required to mount effective antifungal immunity in the oral cavity, and they are nonredundant," says Dr. Aggor.

Where the Research is Headed

There are several implications to Dr. Aggor’s research, both in oral antifungal immunity and other areas of study beyond candidiasis and fungal infection. 

One of the implications from the studies may be for oral cancers. It is known that most oral cancers begin in the basal epithelium. Other studies have shown roles for the IL-22 receptor and STAT3 in, for example, colon cancer.

“Further projections from our work may lead to examination of the IL-22 receptor and STAT3 in the basal epithelium to better understand potential factors driving the production of cancer cells, especially those of oral cancers," says Dr. Aggor. "Another direction for my future studies, and something I am already beginning to examine more in-depth, is to explore the integrated signals between IL-22 and IL-17 receptors in the oral cavity. My goal is to have preliminary findings of how these signals function to drive protection in fungal infection within the next year or two. 

More About Dr. Aggor

Felix E.Y. Aggor, PhD, is a postdoctoral member of the Gaffen Laboratory at the University of Pittsburgh. Dr. Aggor earned his doctorate in Microbiology and Immunology from the University of Pittsburgh School of Medicine in 2020. Prior to studying at the University of Pittsburgh, Dr. Aggor earned his BSc and MPhil in Biochemistry from the University of Ghana Legon. 

Dr. Aggor’s studies in his home country of Ghana began as a path toward his becoming a physician. His pursuit of a career in medicine was greatly shaped by experiences he had immediately after completing his undergraduate degree when he contracted malaria and spent a significant amount of time in treatment and recovery. These experiences helped shape his desire for a career in medicine. However, during his first year of medical school, a familial crisis necessitated an interruption in his training. His studies then pivoted to research work in malaria vaccines and sickle cell disease at the Noguchi Memorial Institute for Medical Research and Korle-Bu Teaching Hospital in Ghana. These led to his growing interest in immunology and, ultimately, his PhD studies at the University of Pittsburgh in the Gaffen Laboratory.

Dr. Aggor’s research interests primarily involve fungal immunology, Th17 cells and cytokines in extracellular infections and autoimmunity, and vaccine development. Dr. Aggor’s doctoral dissertation was on the subject of “Mechanistic Insights Into the Roles of IL-22/IL-22RA1 Axis in Oral Anti-Fungal Immunity.”  During his graduate training at Pitt, Dr. Aggor received numerous awards. Prominent among them, in November 2020, Dr. Aggor was awarded the University of Pittsburgh BGSA Steven Phillips Award for the Best Student-Authored Publication for his IL-22 paper discussed above. Since 2008, The Gaffen Laboratory, led by Sarah Gaffen, PhD, has made enormous contributions to defining the molecular mechanisms of cytokine function in autoimmunity and beyond.

“I have a great interest in combining clinical practice and research because what has fascinated me the most in my research career are those studies that translate from the bench to the bedside,” says Dr. Aggor. “I will therefore be pursuing the option of going back to medical school.”

Reference

1. Aggor FEY, Break TJ, Trevejo-Nuñez G, Whibley N, Coleman BM, Bailey RD, Kaplan DH, Naglik JR, Shan W, Shetty AC, McCracken C, Durum SK, Biswas PS, Bruno VM, Kolls JK, Lionakis MS, Gaffen SL. Oral Epithelial IL-22/STAT3 Signaling Licenses IL-17-Mediated Immunity to Oral Mucosal Candidiasis. Sci Immunol. 2020 Jun 5; 5(48): eaba0570. doi: 10.1126/sciimmunol.aba0570.

Watch a video of Dr. Aggor and Dr. Gaffen discussing the findings from their IL-22 paper.

Further Reading

Other papers authored by Dr. Aggor include:

Aggor FEY, Way SS, Gaffen SL. Fungus Among Us: The Frenemies Within. Trends Immunol. 2019 Jun; 40(6): 469-471. 

Peters BM, Coleman BM, Willems HME, Barker KS, Aggor FEY, Cipolla E, Verma AH, Bishu S, Huppler AH, Bruno VM, Gaffen SL. The Interleukin (IL) 17R/IL-22R Signaling Axis Is Dispensable for Vulvovaginal Candidiasis Regardless of Estrogen Status. J Infect Dis. 2020 Apr 7; 221(9): 1554-1563. 

Kusi KA, Aggor FE, Amoah LE, Anum D, Nartey Y, Amoako-Sakyi D, Obiri-Yeboah D, Hollingdale M, Ganeshan H, Belmonte M, Peters B, Kim Y, Tetteh J, Kyei-Baafour E, Dodoo D, Villasante E, Sedegah M. Identification of Plasmodium Falciparum Circumsporozoite Protein-Specific CD8+ T Cell Epitopes in a Malaria Exposed Population. PLoS One. 2020 Feb 10; 15(2): e0228177.

Kusi KA, Aguiar J, Kumordjie S, Aggor F, Bolton J, Renner A, Kyei-Baafour E, Puplampu N, Belmonte M, Dodoo D, Gyan BA, Ofori MF, Oduro AR, Atuguba F, Koram KA, Adams N, Letizia A, Villasante E, Sedegah M. Antigenicity and Immune Correlate Assessment of Seven Plasmodium Falciparum Antigens in a Longitudinal Infant Cohort From Northern Ghana. Sci Rep. 2019 Jun 13; 9(1): 8621.

Trevejo-Nunez G, Elsegeiny W, Aggor FEY, Tweedle JL, Kaplan Z, Gandhi P, Castillo P, Ferguson A, Alcorn JF, Chen K, Kolls JK, Gaffen SL. Interleukin-22 (IL-22) Binding Protein Constrains IL-22 Activity, Host Defense, and Oxidative Phosphorylation Genes During Pneumococcal Pneumonia. Infect Immun. 2019 Oct 18; 87(11): e00550-19. 

Zhou C, Monin L, Gordon R, Aggor FEY, Bechara R, Edwards TN, Kaplan DH, Gingras S, Gaffen SL.
An IL-17F.S65L Knock-In Mouse Reveals Similarities and Differences in IL-17F Function in Oral Candidiasis: A New Tool to Understand IL-17F. J Immunol. 2020 Aug 1; 205(3): 720-730.