A dormant T-cell population with autoimmune potential exhibits low self-reactivity and infiltrates islets in type 1 diabetes

The contribution of low-affinity T cells to autoimmunity in the context of polyclonal T-cell responses is understudied due to the limitations in their capture by tetrameric reagents and low level of activation in response to antigenic stimulation. As a result, low-affinity T cells are often disregarded as nonantigen-specific cells irrelevant to the immune response. Our study aimed to assess how the level of self-antigen reactivity shapes T-cell lineage and effector responses in the context of spontaneous tissue-specific autoimmunity observed in NOD mice. Using multicolor flow cytometry in combination with Nur77(GFP) reporter of TCR signaling, we identified a dormant population of T cells that infiltrated the pancreatic islets of prediabetic NOD mice, which exhibited reduced levels of self-tissue reactivity based on expression of CD5 and Nur77(GFP). We showed that these CD5(low) T cells had a unique TCR repertoire and exhibited low activation and minimal effector function; however, induced rapid diabetes upon transfer. The CD4(+)CD5(low) T-cell population displayed transcriptional signature of central memory T cells, consistent with the ability to acquire effector function post-transfer. Transcriptional profile of CD5(low) T cells was similar to T cells expressing a low-affinity TCR, indicating TCR affinity to be an important factor in shaping CD5(low) T-cell phenotype and function at the tissue site. Overall, our study suggests that autoimmune tissue can maintain a reservoir of undifferentiated central memory-like autoreactive T cells with pathogenic effector potential that might be an important source for effector T cells during long-term chronic autoimmunity.

Automated summary

The contribution of low-affinity T cells to autoimmunity has been understudied due to limitations in detection methods. Our study found a population of low-affinity T cells in the pancreatic islets of prediabetic NOD mice, which exhibited reduced reactivity to self-tissue and minimal effector function but induced rapid diabetes upon transfer. These cells had transcriptional characteristics of central memory T cells and relied on TCR affinity to shape their phenotype and function. Our findings suggest that low-affinity T cells may play an important role in long-term chronic autoimmunity.