Regulatory potential and control ofFoxp3expression in newborn CD4⁺T cells

Abstract

Thymectomy at day 3 after birth leads to autoimmune disease in some genetic backgrounds. Disease is thought to be caused by the lack͞paucity of regulatory T cells. We show that 3-day-old mice already contain a significant compartment of Foxp3-expressing CD25 ؉ CD4 ؉ splenocytes. Whereas, in adult spleen, the subsets of regulatory T cells (CD25 ؉ and͞or CD103 ؉ ) express high amounts of Foxp3 mRNA, in 3-day-old mice, both thymic and splenic CD25 ؉ CD4 ؉ T cell subsets express lower amounts of Foxp3 mRNA, and CD103 ؉ cells are barely detected. In adult day 3-thymectomized mice, the CD25 ؉ CD4 ؉ T cell subset is overrepresented (most of the cells being CD103 ؉ ) and expresses high amounts of Foxp3 mRNA, independent of the development of autoimmune gastritis. These cells control inflammatory bowel disease and the homeostatic expansion of lymphocytes. This study demonstrates that the peripheral immune system of newborn mice is endowed of a remarkable regulatory potential, which develops considerably in the absence of thymic supply. R egulatory T cells belonging to the natural pool of CD25 ϩ CD4 ϩ T cells play a fundamental role in the maintenance of peripheral tolerance to self-antigens (1-3) and in the regulation of adaptive (4-7) and innate (8) immune responses against pathogens. Because of their capacity of efficiently inhibit T cell proliferation (9, 10), these cells are a key element in the systemic homeostatic mechanisms that control total lymphocyte numbers (10). The transcription factor Scurfin, encoded by the forkhead͞winged helix (Foxp3) gene (11), is a specific marker for regulatory activity (12) and is essential for the development and function of regulatory CD25 Little is known on the ontogeny of the peripheral compartment of regulatory CD4 ϩ T cells. It is now established that at least part of the regulatory CD25 ϩ CD4 ϩ T cells are produced in the thymus (22, 23). However, it has been proposed that they are only significantly exported to the periphery after the third day of postnatal life (2). This hypothesis is based on the observation that mice thymectomized between days 2 and 4 after birth develop organ-specific autoimmune disorders, which are prevented by the early transfer of adult CD25 ϩ CD4 ϩ T cells (2). However, the pattern and the incidence͞severity of these diseases vary among animals of the same strain and are highly dependent on their genetic background (24,25). Indeed, in several strains, day 3 neonatal thymectomy does not lead to the development of autoimmune diseases despite inducing lymphopenia. Moreover, even in sensitive strains, thymectomized mice do not develop some types of inflammatory diseases, such as inflammatory bowel disease (IBD), and keep a long-lasting state of lymphopenia (2). All of these features are in sharp contrast with the syndrome resulting from the inactivation of the Foxp3 gene in the C57BL͞6 mice, a strain resistant to neonatal thymectomy-induced autoimmune disease. In this case, the complete absence of regulatory CD25 ϩ CD4 ϩ T cells leads to generalized lymph...

Cutting Edge: Autoimmune Disease in Day 3 Thymectomized Mice Is Actively Controlled by Endogenous Disease-Specific Regulatory T Cells

“…Our findings confirm the observations of Dujardin et al (12); in d3tx mice, functional Treg, now identified as Foxp3 ϩ CD4 ϩ T cells, are persistently increased relative to the CD25 Ϫ effector T cells. To extend the study, we investigated the in vivo function of Treg in d3tx mice, in particular their capacity to influence autoimmune diseases that develop in d3tx mice (5).…”

“…Pivotal support for the Treg-depletion hypothesis of d3tx disease was provided by the reported late ontogeny of Treg development (9, 10), but the supporting data are controversial (10,12). More importantly, there has not been an attempt to investigate the in vivo function of neonatal Treg, specifically their capacity to suppress the autoimmune disease of the d3tx mice.…”

“…In 2004, Dujardin et al (12) reported that the percentage of CD25 ϩ CD4 ϩ T cells in the spleens of d3tx BALB/c mice was increased over untreated mice (Ͼ20 vs Ͻ10%). The CD25 ϩ T *Department of Pathology, University of Virginia, Charlottesville, VA 22908; † Department of Biology, Indiana University-Purdue University, Indianapolis, Indianapolis, IN 46202; and ‡ Department of Medicine and Pathology, University of Vermont, Burlington, VT 05405 cell population expressed Forkhead box p3 (Foxp3) mRNA, suppressed in vitro polyclonal anti-CD3 stimulated CD25 Ϫ T cell responses, and prevented colitis in scid recipients of CD25 Ϫ T effector cells.…”

“…The CD25 ϩ T *Department of Pathology, University of Virginia, Charlottesville, VA 22908; † Department of Biology, Indiana University-Purdue University, Indianapolis, Indianapolis, IN 46202; and ‡ Department of Medicine and Pathology, University of Vermont, Burlington, VT 05405 cell population expressed Forkhead box p3 (Foxp3) mRNA, suppressed in vitro polyclonal anti-CD3 stimulated CD25 Ϫ T cell responses, and prevented colitis in scid recipients of CD25 Ϫ T effector cells. Thus there is a fractional increase in functional Treg in the CD4 ϩ T cell compartment of d3tx mice (12). However, Dujardin et al (12) did not directly examine the capacity of Treg to suppress autoimmune diseases known to occur in d3tx mice (AOD and AIG), thereby leaving open the question of whether Treg deficiency is the mechanism underlying d3Tx-induced autoimmune disease (9).…”

“…Thus there is a fractional increase in functional Treg in the CD4 ϩ T cell compartment of d3tx mice (12). However, Dujardin et al (12) did not directly examine the capacity of Treg to suppress autoimmune diseases known to occur in d3tx mice (AOD and AIG), thereby leaving open the question of whether Treg deficiency is the mechanism underlying d3Tx-induced autoimmune disease (9). Also, colitis is not relevant to d3tx because it does not occur in d3tx mice (4).…”