Phenotypical and functional characterization of murine iNKT1, 2, and 17 cells.
Final Report Abstract
In the recent years there was a boost in the research addressing the development and function of murine invariant natural killer T (iNKT) cells in thymus. This was propelled by a change of paradigm. According to the classical model of linear development established more than 20 years ago, iNKT cell differentiation occurs stepwise and is characterized by a development from immature cells producing mainly IL4 to matured cells secreting IFN. However, among other caveats this model left unexplained the existence of IL17 producing iNKT cells. Later on, a functional classification model was proposed that gained quick acceptance and was further refined in the past years. According to this hypothesis, a committed progenitor can give rise to three main subpopulations: iNKT1 cells, iNKT2 cells, and iNKT17 cells, respectively. Our group has contributed in the past to the characterization of these three subsets in thymus. As a logical next step, we asked in the scope of this DFG-project whether and how the “standard” iNKT subsets as defined by their existence in young adult thymus, would adapt to special conditions. We selected two main scenarios: comparing iNKT cells in young adult thymus to those residing in peripheral compartments or to those present in aged thymus. In both cases, the iNKT cells are exposed to a dramatically altered micro-environment. Total RNA sequencing imaging a cells current phenotypic status served as a platform for these comparisons. In addition, our previous analyses hinted to several candidate genes that might be of general importance for the differentiation and/or function of distinct iNKT subsets. Even though we failed to prove such importance in two cases (Hopx, Blk) this experimental strategy is still promising and should be followed up. Regarding the organ specific expression of iNKT relevant genes, we succeeded in the identification of several interesting candidate genes whose contribution was not investigated thus far in the context of iNKT cell biology. Furthermore, we discovered an iNKT subtype specific impact of IL2 on survival and propagation. At present, the cellular factors mediating the diverse effects remain unclear. Future work should address this issue asking whether factors like NF-kB, ELF-1 or HMGI(Y) that are known to mediate IL2 signaling play a role or whether thus other pathways operate in an iNKT cell specific manner. An influence of aging on the phenotype and function of iNKT cells was already assumed based on previous observations. Interestingly however, regarding cell numbers the process of thymic involution seems to affect iNKT cells to a lesser extent than regular T cells. This may be explained by an ongoing propagation of thymus resident iNKT cells that is absent in regular T cells yet our results would not support this idea. Importantly, we found that the expression of signature genes such as Tbx21 or RORgt were ageinsensitive even though we met with troubles defining a uniform iNKT2 subset in aged thymus that was based on specific surface markers. It appeared that thus far uncharacterized iNKT subpopulations emerge in older thymus that escaped detection in younger animals due to negligible prevalence. The origin and significance of such populations should be addressed in further projects. We identified only very few genes that display a considerable change in expression strength upon aging such as Gzma. Genes that were expressed either in young or aged cells were not discovered.
Publications
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(2020). Impact of Aging on the Phenotype of Invariant Natural Killer T Cells in Mouse Thymus. Front Immunol 11, 575764
Papadogianni, G., Ravens, I., Dittrich-Breiholz, O., Bernhardt, G., and Georgiev, H.
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(2021). The impact of stress on the transcriptomic signature of iNKT1 cells. Biochem Biophys Rep 28, 101163
Papadogianni, G., Ravens, I., Hassan, A., Dittrich-Breiholz, O., Bernhardt, G., and Georgiev, H.
