Fas (CD95/APO-1) limits the expansion of T lymphocytes in an environment of limited T-cell antigen receptor/MHC contacts

A Framework for Understanding Maternal Immunity

This is an alternative and controversial framing of the data relevant to maternal immunity. It argues for a departure from classical theory to view, interrogate and interpret existing data.

A distinct CD38+CD45RA+ population of CD4+, CD8+, and double-negative T cells is controlled by FAS

The identification and characterization of rare immune cell populations in humans can be facilitated by their growth advantage in the context of specific genetic diseases. Here, we use autoimmune lymphoproliferative syndrome to identify a population of FAS-controlled TCRαβ⁺ T cells. They include CD4⁺, CD8⁺, and double-negative T cells and can be defined by a CD38⁺CD45RA⁺T-BET⁻ expression pattern. These unconventional T cells are present in healthy individuals, are generated before birth, are enriched in lymphoid tissue, and do not expand during acute viral infection. They are characterized by a unique molecular signature that is unambiguously different from other known T cell differentiation subsets and independent of CD4 or CD8 expression. Functionally, FAS-controlled T cells represent highly proliferative, noncytotoxic T cells with an IL-10 cytokine bias. Mechanistically, regulation of this physiological population is mediated by FAS and CTLA4 signaling, and its survival is enhanced by mTOR and STAT3 signals. Genetic alterations in these pathways result in expansion of FAS-controlled T cells, which can cause significant lymphoproliferative disease.

Immunoenhancement effects of chitosan-modified ginseng stem-leaf saponins-encapsulated cubosomes as an ajuvant

Nanoparticle delivery of functional molecules and vaccine is a promising method for enhancing the immune response. The objective of this study was to design chitosan (CS)-modified ginseng stem-leaf saponins (GSLS)-encapsulated cubosomes (Cub-GSLS^CS) as a vaccine delivery system and explore its immunologic activity and adjuvanticity. In this study, CS-modified GSLS-encapsulated cubosomes (Cub-GSLS^CS) were prepared. The storage stability of GSLS and that of ovalbumin (OVA) were measured. Additionally, the immunopotentiation of Cub-GSLS^CS were assessed on potentiating macrophage in vitro, and the adjuvant activity was evaluated through immune response triggered by OVA model antigen. The encapsulation efficiency of optimized Cub-GSLS^CS was about 65 % with Im3m nanostructure. The Cub-GSLS^CS showed excellent stability and sustained release for up to 28 days. In vitro, Cub-GSLS^CS nanoparticles improved cellular uptake, stimulated cytokines secretion of IL-6, IL-12, TNF-α, and generated more inducible nitric oxide synthase (iNOS) to produce higher levels of nitric oxide (NO) compared with other groups. Furthermore, the immunoadjuvant effects of OVA encapsulated Cub-GSLSCS nanoparticles (Cub-GSLS^CS-OVA) were observed through immunized mice. Results showed that the ratio of CD4+/CD8 + T lymphocytes was increased in Cub-GSLS^CS-OVA group. In addition, Cub-GSLS^CS-OVA nanoparticles induced dramatically high OVA-specific IgG, IgG1, and IgG2a levels and stimulated the secretion of cytokines. Cub-GSLS^CS may be a potential vaccine delivery system and induce a long-term sustained immunogenicity.

Selective DNA Demethylation Accompanies T Cell Homeostatic Proliferation and Gene Regulation in Lupus-Prone lpr Mice

Systemic lupus erythematosus (SLE) is characterized by increased DNA demethylation in T cells, although it is unclear whether this occurs primarily in a subset of SLE T cells. The process driving the DNA demethylation and the consequences on overall gene expression are also poorly understood and whether this represents a secondary consequence of SLE or a primary contributing factor. Lupus-prone lpr mice accumulate large numbers of T cells with age because of a mutation in Fas (CD95). The accumulating T cells include an unusual population of CD4-CD8-TCR-αβ+ (DN) T cells that arise from CD8+ precursors and are also found in human SLE. We have previously observed that T cell accumulation in lpr mice is due to dysregulation of T cell homeostatic proliferation, which parallels an increased expression of numerous genes in the DN subset, including several proinflammatory molecules and checkpoint blockers. We thus determined the DNA methylome in lpr DN T cells compared with their CD8+ precursors. Our findings show that DN T cells manifest discrete sites of extensive demethylation throughout the genome, and these sites correspond to the location of a large proportion of the upregulated genes. Thus, dysregulated homeostatic proliferation in lpr mice and consequent epigenetic alterations may be a contributing factor to lupus pathogenesis.

The molecular signature of murine T cell homeostatic proliferation reveals both inflammatory and immune inhibition patterns

T lymphocyte homeostatic proliferation, driven by the engagement of T cell antigen receptor with self-peptide/major histocompatibility complexes, and signaling through the common γ-chain-containing cytokine receptors, is critical for the maintenance of the T cell compartment and is regulated by the Fas death receptor (Fas, CD95). In the absence of Fas, Fas-deficient lymphoproliferation spontaneous mutation (lpr) mice accumulate homeostatically expanded T cells. The functional consequences of sequential rounds of homeostatic expansion are not well defined. We thus examined the gene expression profiles of murine wild-type and Fas-deficient lpr CD8+ T cell subsets that have undergone different amounts of homeostatic proliferation as defined by their level of CD44 expression, and the CD4-CD8-TCRαβ+ T cell subset that results from extensive homeostatic expansion of CD8+ T cells. Our studies show that recurrent T cell homeostatic proliferation results in global gene expression changes, including the progressive upregulation of both cytolytic proteins such as Fas-Ligand and granzyme B as well as inhibitory proteins such as programmed cell death protein 1 (PD-1) and lymphocyte activating 3 (Lag3). These findings provide an explanation for how augmented T cell homeostatic expansion could lead to the frequently observed clinical paradox of simultaneous autoinflammatory and immunodeficiency syndromes and provide further insight into the regulatory programs that control chronically stimulated T cells.

Abnormally differentiated CD4+ or CD8+ T cells with phenotypic and genetic features of double negative T cells in human Fas deficiency

Lack of KLRG1 and T-bet expression is a unique feature of DNT and subsets of single positive T cells in ALPS patients. Genetic, phenotypic, and transcriptional evidence indicates that DNT in ALPS patients derive from both CD4+ and CD8+ T cells.

Deletion of microRNA-155 reduces autoantibody responses and alleviates lupus-like disease in the Fas(lpr) mouse

MicroRNA-155 (miR-155) regulates antibody responses and subsequent B-cell effector functions to exogenous antigens. However, the role of miR-155 in systemic autoimmunity is not known. Using the death receptor deficient (Fas(lpr)) lupus-prone mouse, we show here that ablation of miR-155 reduced autoantibody responses accompanied by a decrease in serum IgG but not IgM anti-dsDNA antibodies and a reduction of kidney inflammation. MiR-155 deletion in Fas(lpr) B cells restored the reduced SH2 domain-containing inositol 5'-phosphatase 1 to normal levels. In addition, coaggregation of the Fc γ receptor IIB with the B-cell receptor in miR-155(-/-)-Fas(lpr) B cells resulted in decreased ERK activation, proliferation, and production of switched antibodies compared with miR-155 sufficient Fas(lpr) B cells. Thus, by controlling the levels of SH2 domain-containing inositol 5'-phosphatase 1, miR-155 in part maintains an activation threshold that allows B cells to respond to antigens.

PD-1 regulates T cell proliferation in a tissue and subset-specific manner during normal mouse pregnancy

The regulation of T cell homeostasis during pregnancy has important implications for maternal tolerance and immunity. Evidence suggests that Programmed Death-1 (PD-1) participates in regulation of T cell homeostasis and peripheral tolerance. To examine the contribution of PD-1 signaling on T cell homeostasis during normal mouse pregnancy, we examined T cell number or proportion, PD-1 expression, proliferation, and apoptosis by flow cytometry, BrdU incorporation, and TUNEL assay in pregnant mice given anti-PD-1 blocking antibody or control on days 10, 12, and 14 of gestation. We observed tissue, treatment, and T cell-specific differences in PD-1 expression. Both pregnancy and PD-1 blockade increased T cell proliferation in the spleen, yet this effect was limited to CD4 T cells in the uterine- draining nodes. In the uterus, PD-1 blockade markedly altered the composition of the T cell pool. These studies support the idea that pregnancy is a state of dynamic T cell homeostasis and suggest that this state is partially supported by PD-1 signaling.