Neuropilin 1 is expressed on thymus-derived natural regulatory T cells,but not mucosa-generated induced Foxp3+ T reg cells

Foxp3 activity is essential for the normal function of the immune system. Two types of regulatory T (T reg) cells express Foxp3, thymus-generated natural T reg (nT reg) cells, and peripherally generated adaptive T reg (iT reg) cells. These cell types have complementary functions. Until now, it has not been possible to distinguish iT reg from nT reg cells in vivo based solely on surface markers. We report here that Neuropilin 1 (Nrp1) is expressed at high levels by most nT reg cells; in contrast, mucosa-generated iT reg and other noninflammatory iT reg cells express low levels of Nrp1. We found that Nrp1 expression is under the control of TGF-β. By tracing nT reg and iT reg cells, we could establish that some tumors have a very large proportion of infiltrating iT reg cells. iT reg cells obtained from highly inflammatory environments, such as the spinal cords of mice with spontaneous autoimmune encephalomyelitis (EAE) and the lungs of mice with chronic asthma, express Nrp1. In the same animals, iT reg cells in secondary lymphoid organs remain Nrp1^low. We also determined that, in spontaneous EAE, iT reg cells help to establish a chronic phase of the disease.The powerful effects of Foxp3⁺ regulatory T cells are illustrated by the devastating inflammatory diseases caused by Foxp3 mutations in mice and humans (Bennett et al., 2001; Brunkow et al., 2001; Wildin et al., 2001). As a consequence, experimental or clinical manipulation of the entire Foxp3⁺ T reg compartment could have catastrophic consequences (Kim et al., 2007).It has been proposed that, because of their different developmental origin and TCR repertoires, Foxp3⁺ nT reg and iT reg cells could have some nonoverlapping regulatory functions in vivo (Bluestone and Abbas, 2003; Curotto de Lafaille and Lafaille, 2009; Haribhai et al., 2009). It was recently shown that to completely prevent mortality and inflammation in Foxp3-deficient mice, both nT reg and iT reg cells were necessary (Bilate and Lafaille, 2011; Haribhai et al., 2011).The nonoverlapping functions of nT reg and iT reg cells raise the possibility of selective intervention strategies that would not affect all T reg cells—only nT reg or iT reg cells, or subsets of them. A major barrier to such an approach is the lack of suitable surface markers that distinguish nT reg and iT reg cell populations. The aforementioned studies addressing the issue of division of labor required very specialized strains of mice. However, these experimental systems cannot be used to identify nT reg and iT reg cells in unmanipulated WT mice. In this study, we show that surface expression of Neuropilin 1 (Nrp1) is preferentially up-regulated by nT reg cells in WT mice, and that, in contrast, iT reg cells generated under several in vivo conditions, including the physiologically relevant mucosal route, express low levels of surface Nrp1.