Molecular and functional characterization of resident CD4$^{+}$ T cells in lymphoid organs

Kaminski, Anne Carina; Huber, Michael (Thesis advisor); Pabst, Oliver (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2020


Adaptive immunity relies on controlled T cell migration and appropriate T cell positioning within peripheral and lymphoid tissues. Antigen-experienced T cells patrol lymph nodes (LN), peripheral tissues or remain tissue resident. Within these compartments, T cells are strategically positioned to provide a fast response upon encounter of their cognate antigen. However, in contrast to tissue resident T cells, T cell resident in LN have not been studied in detail, largely due to a lack of appropriate techniques. In this thesis we use photoconversion-based in vivo cell tracking, in a novel transgenic mouse model, to study the generation, maintenance and function of LN resident CD4+ T cells. We identified antigen-experienced resident CD4+ T cells in all examined LNs, and demonstrated that they constitute a substantial proportion of the CD4+ CD62Llo population. Resident CD4+ T cells are long-lived and can be detected in LNs for at least 8 weeks. They are characterised by an enriched CD69 expression and a low rate of proliferation. However, upon stimulation, LN resident T cells retained the ability to proliferate, indicating that they retain responsiveness to stimulation. The frequency of LN resident T cells was unaltered under long-term antibiotic treatment or after feeding of a protein-free diet, suggesting that microbiota or food antigens are not crucial for their generation and/or maintenance. Additionally, LN resident CD4+ T cells were maintained in a model of induced T cell receptor (TCR) deficiency. These data indicate that residency is not a consequence of continuous antigen exposure in the LNs. However, even though a constant TCR signal was not required to maintain resident T cells, exposure to cognate antigen was sufficient to generate LN resident T cells in the draining LN. It is therefore likely that the LN-resident CD4+ T cells represent an antigen-experienced population, locally generated in the LN and maintained either by TCR-independent signals or epigenetic modification. Importantly, we show that LN resident CD4+ T cells are a heterogeneous population, with the majority of LN resident CD4+ T cells being FoxP3+ Tregs. Vice versa, the majority of all CD62Llo Tregs are resident in the LN. A microarray analysis revealed a transcriptional signature characterised by a downregulation of genes involved in cell cycle and metabolism in LN resident Tregs. Notably, the TCR repertoire is not shared between resident Tregs in different LNs, which suggests that LN resident Tregs are generated locally. We therefore propose that LN resident Tregs are generated locally to be strategically positioned in the LN to prevent priming of adverse T cell responses, thereby facilitating immune homeostasis. In line with this hypothesis, we could show that LN resident Tregs effectively suppress T cell proliferation in vitro and were able to prevent colitogenic T cell responses in vivo. We speculate that LN resident T cells could therefore be an important therapeutic target for T cell mediated diseases such as inflammatory bowel disease.