CD28 signaling in T regulatory precursors requires p56lck and rafts integrity to stabilize the Foxp3 message.

Naturally occurring CD4(+)25(high)Foxp3(+) T regulatory (T-reg) cells are critical for maintaining tolerance to self and non-self Ags. The Foxp3 master-regulatory gene and CD28 costimulation are both required for thymic development and suppressogenic function of CD4(+)25(high)Foxp3(+) T-regs. Herein, we show that the sole CD28 stimulation of T-reg thymic precursors augments Foxp3 expression through the increase in Foxp3 mRNA life span by a mechanism involving p56(lck) and its binding motif on CD28 cytosolic tail, as well as the lipid rafts. We found that 1) the glycosphingolipids and cholesterol components of lipid rafts were highly expressed and unusually partitioned in T-reg thymic precursors as compared with the conventional T cell precursors, 2) the CD28 receptor density on cell membrane is proportional with the content of cholesterol in lipid rafts and with the level of Foxp3 mRNA expression in T-reg precursors, and 3) the CD28-mediated increase of Foxp3 mRNA life span was paralleled by an increased proliferative and suppressogenic capacity of terminally differentiated CD4(+)25(high)Foxp3(+) T-reg precursors. Thus, the functional integrity of CD28 receptor p56(lck) and plasma membrane lipid rafts are all prerequisites for up-regulation and long-term expression of Foxp3 mRNA transcripts in CD4(+)25(high)Foxp3(+) T-reg precursors.

Increased membrane cholesterol in lymphocytes diverts T-cells toward an inflammatory response.

Cell signaling for T-cell growth, differentiation, and apoptosis is initiated in the cholesterol-rich microdomains of the plasma membrane known as lipid rafts. Herein, we investigated whether enrichment of membrane cholesterol in lipid rafts affects antigen-specific CD4 T-helper cell functions. Enrichment of membrane cholesterol by 40-50% following squalene administration in mice was paralleled by an increased number of resting CD4 T helper cells in periphery. We also observed sensitization of the Th1 differentiation machinery through co-localization of IL-2Rα, IL-4Rα, and IL-12Rß2 subunits with GM1 positive lipid rafts, and increased STAT-4 and STAT-5 phosphorylation following membrane cholesterol enrichment. Antigen stimulation or CD3/CD28 polyclonal stimulation of membrane cholesterol-enriched, resting CD4 T-cells followed a path of Th1 differentiation, which was more vigorous in the presence of increased IL-12 secretion by APCs enriched in membrane cholesterol. Enrichment of membrane cholesterol in antigen-specific, autoimmune Th1 cells fostered their organ-specific reactivity, as confirmed in an autoimmune mouse model for diabetes. However, membrane cholesterol enrichment in CD4(+)Foxp3(+) T-reg cells did not alter their suppressogenic function. These findings revealed a differential regulatory effect of membrane cholesterol on the function of CD4 T-cell subsets. This first suggests that membrane cholesterol could be a new therapeutic target to modulate the immune functions, and second that increased membrane cholesterol in various physiopathological conditions may bias the immune system toward an inflammatory Th1 type response.

Differential effect of CD4+Foxp3+ T-regulatory cells on the B and T helper cell responses to influenza virus vaccination.

The T-regulatory (T-reg) cells restrict the T-cell functions in various viral infections including influenza infection. However little is known about the effect of T-regs in influenza vaccination. Herein, we found that immunization of BALB/c mice with a prototype of UV-inactivated influenza PR8/A/34 virus vaccine expanded the CD4(+)Foxp3(+) T-reg pool and fostered the development of virus-specific CD4(+)Foxp3(+) T-reg cells. Increasing the size of Foxp3(+) T-reg pool did not alter the primary PR8-specific B-cell response, but it did suppress the primary and memory PR8-specific T helper responses induced by vaccination. In contrast, the vaccination-induced T helper cell response was augmented in the absence of CD4(+)Foxp3(+) T-reg cells. Since CD4 T helper cells contribute to anti-influenza protection, therapeutic "quenching" of T-reg function prior to vaccination may enhance the efficacy of influenza vaccination.

Double negative (CD3+ 4- 8-) TCR alphabeta splenic cells from young NOD mice provide long-lasting protection against type 1 diabetes.

BACKGROUND: Double negative CD3(+)4(-)8(-) TCR alphabeta splenic cells (DNCD3) can suppress the immune responses to allo and xenografts, infectious agents, tumors, and some autoimmune disorders. However, little is known about their role in autoimmune diabetes, a disease characterized by the reduction of insulin production subsequent to destruction of pancreatic beta-cells by a polyclonal population of self-reactive T-cells. Herein, we analyzed the function and phenotype of DNCD3 splenic cells in young NOD mice predisposed to several autoimmune disorders among which, the human-like autoimmune diabetes. METHODOLOGY/PRINCIPAL FINDINGS: DNCD3 splenic cells from young NOD mice (1) provided long-lasting protection against diabetes transfer in NOD/Scid immunodeficient mice, (2) proliferated and differentiated in the spleen and pancreas of NOD/Scid mice and pre-diabetic NOD mice into IL-10-secreting T(R)-1 like cells in a Th2-like environment, and (3) their anti-diabetogenic phenotype is CD3(+)(CD4(-)CD8(-))CD28(+)CD69(+)CD25(low) Foxp3(-) iCTLA-4(-)TCR alphabeta(+) with a predominant Vbeta13 gene usage. CONCLUSIONS/SIGNIFICANCE: These findings delineate a new T regulatory component in autoimmune diabetes apart from that of NKT and CD4(+)CD25(high) Foxp3(+)T-regulatory cells. DNCD3 splenic cells could be potentially manipulated towards the development of autologous cell therapies in autoimmune diabetes.