ABSTRACT
In this report, we show that the formation of germinal center (GC)-like structures to thymus-independent type 2 antigens in mice depends on intact signals through CD40, but does not depend on T cell-derived CD40-ligand (CD154). In addition, we show that follicular dendritic cells (FDC) are also critical to thymus-independent GC formation, as their depletion by blockade of lymphotoxin-beta receptor signals abrogated GC development unless the responding B cells bound antigen with high affinity. Further evidence that immune complexes drove this CD40-dependent B cell proliferation was provided by the observation that an antibody that detects immune complexes containing complement component 4 on FDC also inhibited thymus-independent GC formation when injected in vivo at the time of immunization. Finally, we show that thymus-independent B cell proliferation was associated with class switching to IgG3, as IgG3(+) antigen-specific switched B cells could be visualized directly in GC, suggesting that immune complexes can provide the signals for class switching within GC in the absence of CD154.
Subject(s)
Antigens, T-Independent/immunology , CD40 Antigens/physiology , CD40 Ligand/physiology , Germinal Center/immunology , Germinal Center/metabolism , Thymus Gland/immunology , Animals , CD40 Antigens/genetics , CD40 Ligand/genetics , Female , Immunoglobulin Class Switching/genetics , Immunoglobulin G/genetics , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Spleen/cytology , Spleen/immunology , Spleen/metabolism , Thymus Gland/cytology , Thymus Gland/metabolismABSTRACT
Recently, we reported that a CD4(+)CD3(-)CD11c(-) accessory cell provided OX40-dependent survival signals to follicular T cells. These accessory cells express both OX40 ligand and CD30 ligand, and the receptors, OX40 and CD30, are both expressed on Th2-primed CD4 T cells. OX40 and CD30 signals share common signaling pathways, suggesting that CD30 signals might substantially compensate in OX40-deficient mice. In this report we have dissected the signaling roles of CD30 alone and in combination with OX40. CD30-deficient mice showed an impaired capacity to sustain follicular germinal center responses, and recall memory Ab responses were substantially reduced. Deficiencies in OX40 and CD30 signals were additive; secondary Ab responses were ablated in double-deficient mice. Although the initial proliferation of OX40/CD30 double-knockout OTII transgenic T cells was comparable to that of their normal counterparts, they failed to survive in vivo, and this was associated with reduced T cell numbers associated with CD4(+)CD3(-) cells in B follicles. Finally, we show that OX40/CD30 double-knockout OTII transgenic T cells fail to survive compared with normal T cells when cocultured with CD4(+)CD3(-) cells in vitro.
Subject(s)
Antibody Formation , CD4-Positive T-Lymphocytes/immunology , Immunologic Memory , Ki-1 Antigen/immunology , Receptors, Tumor Necrosis Factor/immunology , Animals , CD4-Positive T-Lymphocytes/cytology , Cell Survival , Coculture Techniques , Germinal Center/immunology , Ki-1 Antigen/genetics , Membrane Glycoproteins/immunology , Mice , Mice, Knockout , OX40 Ligand , Receptors, OX40 , Receptors, Tumor Necrosis Factor/deficiency , Signal Transduction/immunology , Tumor Necrosis FactorsABSTRACT
In this study we examined the role and regulation of OX40 signals during CD4 T cell priming on dendritic cells (DCs). Contrary to expectation, OX40-deficient cells proliferated more rapidly than their normal counterparts, particularly when stimulated with peptide in the absence of added cytokines. This proliferative advantage was not apparent for Th2-differentiated cells. When the reasons for this were investigated, we found that the cytokine IL-4 specifically down-regulated expression of OX40 ligand on T, B, and DCs, but not on the CD4(+)CD3(-) cells linked with selection of Th2 cells into the memory compartment. OX40 ligand expression was also down-regulated on rapidly proliferating Th1 effectors. These data are compatible with OX40 signals acting during priming as a check on naive T cell proliferation while T cells integrate additional DC signals. This would serve to limit inappropriate T cell responses. In contrast, OX40 signals from CD4(+)CD3(-) cells located in the outer T zone select proliferating Th2 effectors into the memory T cell pool.
Subject(s)
CD4-Positive T-Lymphocytes/immunology , Dendritic Cells/immunology , Growth Inhibitors/physiology , Interleukin-4/physiology , Lymphocyte Activation/immunology , Receptors, Tumor Necrosis Factor/physiology , Signal Transduction/immunology , Th2 Cells/immunology , Animals , B-Lymphocytes/immunology , B-Lymphocytes/metabolism , CD3 Complex/metabolism , CD4-Positive T-Lymphocytes/cytology , CD4-Positive T-Lymphocytes/metabolism , Cell Differentiation/genetics , Cell Differentiation/immunology , Cell Division/genetics , Cell Division/immunology , Cell Proliferation , Cells, Cultured , Dendritic Cells/metabolism , Down-Regulation/immunology , Growth Inhibitors/antagonists & inhibitors , Ligands , Lymphocyte Activation/genetics , Membrane Glycoproteins/antagonists & inhibitors , Membrane Glycoproteins/biosynthesis , Mice , Mice, Inbred C57BL , Mice, Knockout , Mice, Transgenic , OX40 Ligand , Receptors, OX40 , Receptors, Tumor Necrosis Factor/antagonists & inhibitors , Receptors, Tumor Necrosis Factor/deficiency , Receptors, Tumor Necrosis Factor/genetics , Signal Transduction/genetics , Th1 Cells/cytology , Th1 Cells/immunology , Th1 Cells/metabolism , Th2 Cells/cytology , Th2 Cells/metabolism , Tumor Necrosis FactorsABSTRACT
It is well established that CD4(+)CD25(+) regulatory T cells (Tregs) inhibit autoimmune pathology. However, precisely how the behavior of disease-inducing T cells is altered by Tregs remains unclear. In this study we use a TCR transgenic model of diabetes to pinpoint how pathogenic CD4 T cells are modified by Tregs in vivo. We show that although Tregs only modestly inhibit CD4 cell expansion, they potently suppress tissue infiltration. This is associated with a failure of CD4 cells to differentiate into effector cells and to up-regulate the IFN-gamma-dependent chemokine receptor CXCR-3, which confers the ability to respond to pancreatic islet-derived CXCL10. Our data support a model in which Tregs permit T cell activation, yet prohibit T cell differentiation and migration into Ag-bearing tissues.
Subject(s)
CD4-Positive T-Lymphocytes/immunology , Cell Movement/immunology , Cytokines/metabolism , Receptors, Chemokine/genetics , Receptors, Interleukin-2/immunology , Animals , CD4-Positive T-Lymphocytes/metabolism , Diabetes Mellitus/chemically induced , Diabetes Mellitus/genetics , Disease Models, Animal , Interferon-gamma/metabolism , Islets of Langerhans/immunology , Mice , Receptors, CXCR3 , Receptors, Chemokine/biosynthesis , Receptors, Chemokine/immunologyABSTRACT
In this report we identify an accessory cell that interacts with primed and memory T cells at sites where they collaborate with B cells. These cells are distinguished from conventional dendritic cells by their lack of response to Flt3 ligand and their inability to process antigen. Unlike dendritic cells, the CD4(+)CD3(-) cells have little CD80 or CD86 expression but do express high levels of the TNF ligands, OX40 ligand and CD30 ligand. We show that Th2-primed cells express the receptors for these TNF ligands and preferentially survive when cocultured with these cells. Furthermore, we show that the preferential survival of OX40(+) T cells and support of memory T cell help for B cells are linked to their association with CD4(+)CD3(-) cells in vivo.
Subject(s)
B-Lymphocytes/immunology , CD4-Positive T-Lymphocytes/immunology , Ki-1 Antigen/immunology , Lymphocyte Cooperation , Membrane Glycoproteins/immunology , Animals , Antigen-Presenting Cells/immunology , Coculture Techniques , Mice , Microscopy, Confocal , OX40 Ligand , Signal Transduction/immunology , Spleen/cytology , Spleen/immunology , Th1 Cells/immunology , Th2 Cells/immunology , Tumor Necrosis FactorsABSTRACT
CD4 T cell activation is positively (CD28) and negatively (CTLA-4) regulated by the costimulatory ligands CD80 and CD86. A central question is how the balance between these two opposing forces is controlled as T cells differentiate. We have previously shown that CD28 signaling is absolutely required to prime naive CD4 T cells to differentiate into effectors that provide help for germinal centers and class-switched Ab responses. In this study, we show that the requirement for CD28 signaling is transient and effector CD4 T cells do not require CD28 signals to sustain their function. The CD28 independence of effector T cells within germinal centers suggested that a key function for CD80/CD86 under these circumstances might be to provide negative regulatory signals via the CD28 homologue CTLA-4. By examining germinal center responses in mice where the ability to signal through T cell CTLA-4 was compromised, we provide data that supports a critical role for CTLA-4 in down-regulating T cell help for germinal center B cells.