PPARγ in dendritic cells and T cells drives pathogenic type-2 effector responses in lung inflammation.

Type-2 immune responses are well-established drivers of chronic inflammatory diseases, such as asthma, and represent a large burden on public health systems. The transcription factor PPARγ is known to promote M2-macrophage and alveolar macrophage development. Here, we report that PPARγ plays a key role in both T cells and dendritic cells (DCs) for development of type-2 immune responses. It is predominantly expressed in mouse Th2 cells in vitro and in vivo as well as human Th2 cells from allergic patients. Using conditional knockouts, we show that PPARγ signaling in T cells, although largely dispensable for IL-4 induction, is critical for IL-33-driven Th2 effector function in type-2 allergic airway responses. Furthermore, we demonstrate that IL-4 and IL-33 promote up-regulation of PPARγ in lung-resident CD11b+ DCs, which enhances migration to draining lymph nodes and Th2 priming capacity. Thus, we uncover a surprising proinflammatory role for PPARγ and establish it as a novel, important mediator of DC-T cell interactions in type-2 immunity.

T-cell epitope conservation across allergen species is a major determinant of immunogenicity.

BACKGROUND: Patients with pollen allergies are frequently polysensitized. Pollens contain epitopes that are conserved across multiple species. OBJECTIVE: We sought to demonstrate that cross-reactive T cells that recognize conserved epitopes show higher levels of expansion than T cells recognizing monospecific epitopes because of more frequent stimulation. METHOD: RNA was sequenced from 9 pollens, and the reads were assembled de novo into more than 50,000 transcripts. T-cell epitopes from timothy grass (Phleum pratense) were examined for conservation in these transcripts, and this was correlated to their ability to induce T-cell responses. T cells were expanded in vitro with P pratense-derived peptides and tested for cross-reactivity to pollen extracts in ELISpot assays. RESULTS: We found that antigenic proteins are more conserved than nonimmunogenic proteins in P pratense pollen. Additionally, P pratense epitopes that were highly conserved across pollens elicited more T-cell responses in donors with grass allergy than less conserved epitopes. Moreover, conservation of a P pratense peptide at the transcriptomic level correlated with the ability of that peptide to trigger T cells that were cross-reactive with other non-P pratense pollen extracts. CONCLUSION: We found a correlation between conservation of peptides in plant pollens and their T-cell immunogenicity within P pratense, as well as their ability to induce cross-reactive T-cell responses. T cells recognizing conserved epitopes might be more prominent because they can be stimulated by a broader range of pollens and thereby drive polysensitization in allergic donors. We propose that conserved peptides could potentially be used in diagnostic or immunomodulatory approaches that address the issue of polysensitization and target multiple pollen allergies.