Abstract
Purpose: :
Analyses of inflammation-inducing Th cells revealed that a proportion of these cells express both IFN-γ and IL-17, suggesting that certain Th cells may switch their phenotype. The identity of the phenotype switching population has remained unresolved for several years, and here we used a system of transgenic mice we developed to identify this Th population.
Methods: :
Polarized Th1 and Th17 cell lines, expressing hen egg lysozyme (HEL)-specific transgenic T-cell receptor, were generated by repeated activation of naive HEL-specific CD4 cells in the presence of polarizing cocktails. Polarized cells were then transferred into recipient mice expressing HEL in their lens, to induce ocular inflammation. On days 5 and 10 post cell transfer, the phenotype of transferred Th1 and Th17 cells in the recipient eye was determined according to intracellular expression of IFN-γ or IL-17, respectively, using flow cytometry. Phenotypic analysis was also performed in vitro following incubation of polarized Th1 and Th17 cells under the opposite polarizing condition.
Results: :
Whereas no switching to Th17 was detected in eyes of Th1 recipients, substantial proportions of cells expressing IFN-γ, or both IFN-γ and IL-17 were detected in Th17 recipient eyes. The phenotype switch of Th17 cells increased with time and was attributed to exposure to IL-12, a cytokine that is expressed in the inflamed eyes. Moreover, incubation in vitro with Th1-polarizing cocktail, containing IL-12, converted most Th17 into IFN-γ or IFN-γ/IL-17 expressing cells, but no reciprocal conversion was noted with Th1 cells. Also, Th17 cells incubated in Th1 cocktail expressed T-bet, a transcription factor specific to Th1, but Th1 cells did not express ROR-γt, a transcription factor specific to Th17, following incubation in Th17 cocktail.
Conclusions: :
Polarized Th1 cells fully retain their phenotype in these experimental systems. In contrast, Th17 may switch phenotype to express IFN-γ or both IFN-γ and IL-17, as well as T-bet, following exposure to IL-12, in vivo and in vitro.
Keywords: autoimmune disease • inflammation • flow cytometry