The expression of Neuropilin 1 distinguishes regulatory T cells of different Origins

Abstract

Although once proposed to exist and later dismissed, suppressor T cells have, in the last decade and a half, made a major come back in immunology research and been designated `Regulatory T cells'. These cells are extremely potent at preventing immune activation in response to self and environmental antigens, suppressing autoimmune diseases and allergies, and playing a crucial role in the inability of the immune system recognize and attack tumor cells. A key event in the history of Treg cell research was the discovery of the tight association that exists between the expression of the transcription factor Foxp3 and the acquisition of properties of the Treg cell lineage.

It has long been known that Foxp3 Treg cells were generated in the thymus, and these thymic-derived Treg cells were designated naturally-occurring Treg cells, or nTreg cells in short. More recent studies showed that Foxp3 ⁺ Treg cells can also be generated from naïve CD4⁺ T cells in the peripheral organs. The latter Foxp3⁺ Treg cells are designated adaptive or inducible Treg cells, or iTreg in short.

By T cells Receptor (TCR) sequencing studies and experiments, it was shown that nTreg cells have separate and distinct TCR sequences than are expressed on non-Treg (naïve) CD4 T cells. There is also a population of Treg cells that shares it's TCR sequences with the naïve CD4 T cell lineage. This population corresponds to the iTreg cells described above, as it derives from naïve CD4⁺ T cells which acquires Foxp3 and suppressor function outside the thymus.

To distinguish between these two populations of Foxp3-expressing regulatory T cells, we purified extrathymically-derived iTreg cells and compared them to total wild type Treg cells using microarray analysis. We found that Neuropilin 1 (Nrp1), a surface receptor, was differentially regulated between these cell types. Nrp1 has been previously suggested as a Foxp3⁺ Treg cell marker and is known to endow Treg cells with immunomodulatory abilities both in vitro and in vivo.

By confirming the microarray data using realtime qPCR and flow cytometry we were able to determine that two populations of Treg cells exist in wild type mice, a small population of Nrp1^- cells and a larger population of Nrp1⁺ cells, both in peripheral secondary lymphoid organs. In the gut associated lymphoid tissues (GALT) the population of Nrp1 ^- Treg cells was seen to be significantly increased. In the Thymus, the site of nTreg cell development, we found that there is no population of Nrp1^- Foxp3⁺ Single Positive (SP) CD4 T cells. In the thymus there is a population of mature Nrp+ Foxp3⁺ Treg cells and Nrp1^- Foxp3^low immature Treg. This thesis proposes that Nrp1 is an excellent marker of thymic derived Treg cells.