Antigen-specific helper function of cell-free T cell products bearing TCR V beta 8 determinants

Composition and structure of synaptic ectosomes exporting antigen receptor linked to functional CD40 ligand from helper T cells

Planar supported lipid bilayers (PSLB) presenting T cell receptor (TCR) ligands and ICAM-1 induce budding of extracellular microvesicles enriched in functional TCR, defined here as synaptic ectosomes (SE), from helper T cells. SE bind peptide-MHC directly exporting TCR into the synaptic cleft, but incorporation of other effectors is unknown. Here, we utilized bead supported lipid bilayers (BSLB) to capture SE from single immunological synapses (IS), determined SE composition by immunofluorescence flow cytometry and enriched SE for proteomic analysis by particle sorting. We demonstrate selective enrichment of CD40L and ICOS in SE in response to addition of CD40 and ICOSL, respectively, to SLB presenting TCR ligands and ICAM-1. SE are enriched in tetraspanins, BST-2, TCR signaling and ESCRT proteins. Super-resolution microscopy demonstrated that CD40L is present in microclusters within CD81 defined SE that are spatially segregated from TCR/ICOS/BST-2. CD40L+ SE retain the capacity to induce dendritic cell maturation and cytokine production.

Tumor Necrosis Factor Receptor Superfamily in T Cell Priming and Effector Function

The tumor necrosis factor receptor superfamily (TNFRSF) and their ligands mediate lymphoid tissue development and homeostasis in addition to key aspects of innate and adaptive immune responses. T cells of the adaptive immune system express a number of TNFRSF members that are used to receive signals at different instructive stages and produce several tumor necrosis factor superfamily (TNFSF) members as effector molecules. There is also one example of a TNFRSF member serving as a ligand for negative regulatory checkpoint receptors. In most cases, the ligands in afferent and efferent phases are membrane proteins and thus the interaction with TNFRSF members must take place in immunological synapses and other modes of cell-cell interaction. A particular feature of the TNFRSF-mediated signaling is the prominent use of linear ubiquitin chains as scaffolds for signaling complexes that activate nuclear factor κ-B and Fos/Jun transcriptional regulators. This review will focus on the signaling mechanisms triggered by TNFRSF members in their role as costimulators of early and late phases of T cell instruction and the delivery mechanism of TNFSF members through the immunological synapses of helper and cytotoxic effector cells.

Signaling and Polarized Communication Across the T Cell Immunological Synapse

T cells express a somatically recombined antigen receptor (αβTCR) that is calibrated during development to respond to changes in peptides displayed by major histocompatibility complex proteins (pMHC) on the surface of antigen-presenting cells (APC). A key characteristic of pMHC for adaptive immunity is the ability to sample internal states of cells and tissues to sensitively detect changes associated with infection, cell derangement, or tissue injury. Physical T cell-APC contact sets up an axis for polarization of TCR, adhesion molecules, kinases, cytoskeletal elements, and organelles inherent in this mode of juxtacrine signaling. The discovery of further lateral organization of the TCR and adhesion molecules into radially symmetric compartments, the immunological synapse, revealed an intersecting plane of symmetry and potential for regulated symmetry breaking to control duration of T cell-APC interactions. In addition to organizing signaling machinery, the immunological synapse directs the polarized transport and secretion of cytokines and cytolytic agents across the synaptic cleft and is a site for the generation and exocytic release of bioactive microvesicles that can functionally affect recipient APC and other cells in the environment. This machinery is coopted by retroviruses, and human immune deficiency virus-1 may even use antigen-specific synapses for infection of healthy T cells. Here, we discuss recent advances in the molecular and cell biological mechanisms of immunological synapse assembly and signaling and its role in intercellular communication across the synaptic cleft.

T-cells play the classics with a different spin

The immune system uses much of the classic machinery of cell biology, but in ways that put a different spin on organization and function. Striking recent examples include the demonstration of intraflagellar transport protein and hedgehog contributions to the immune synapse, even though immune cells lack a primary cilium that would be the typical setting for this machinery. In a second example, lymphocytes have their own subfamily of integrins, the β2 subfamily, and only integrins in this family form a stable adhesion ring using freely mobile ligands, a key feature of the immunological synapse. Finally, we showed recently that T-cells use endosomal sorting complexes required for transport (ESCRTs) at the plasma membrane to generate T-cell antigen receptor–enriched microvesicles. It is unusual for the ESCRT pathway to operate at the plasma membrane, but this may allow a novel form of cell–cell communication by providing a multivalent ligand for major histocompatibility complex–peptide complexes and perhaps other receptors on the partnering B-cell. Immune cells are thus an exciting system for novel cell biology even with classical pathways that have been studied extensively in other cell types.

What counts in the immunological synapse?

Molecular interactions at the interface between helper T cells and antigen-presenting B cells govern the ability to produce specific antibodies, which is a central event in protective immunity generated by natural infection or man-made vaccines. In order for a T cell to deliver effective help to a B cell and guide affinity maturation, it needs to provide feedback that is proportional to the amount of antigen the B cell collects with its surface antibody. This review focuses on mechanisms by which T and B cells manage to count the products of antigen capture and encourage B cells with the best receptors to dominate the response and make antibody-producing plasma cells. We discuss what is known about the proportionality of T cells responses to presented antigens and consider the mechanisms that B cells may use to keep count of positive feedback from T cells.

Detection of antigen-specific human serum proteins related to the T-cell receptor in infectious disease and in an immune response to milk proteins or chemicals

A monoclonal IgG2 antibody, MG3C9-1 A12, was prepared by immunization of mice with human serum Cohn Fraction III proteins enriched for TCR Ca+ proteins. MG3C9-1 A12 bound to Mr 28,000, antigen-specific TCR Ca+, beta-, and TCR Ca+, beta+ serum proteins associated with TGF-beta1, 2. The IgG2 monoclonal antibody also bound to T-lymphocyte proteins but did not bind to B lymphocyte proteins, human albumin, IgM, IgG, IgA, or TGF-beta1, 2, 3 immunogenic peptides. Monoclonal MG3C9-1 A12 detected TCR-related proteins specific for filarial extract, milk proteins, or benzoic acid in the sera of individuals with chronic or asymptomatic filariasis, milk intolerance, or sensitivity to toluene, respectively. TCR-related serum proteins were also detected intracellularly in mononuclear cells in frozen sections of ileum from a patient with milk intolerance and reactive mesenteric lymph nodes from a patient with a gastric ulcer. The results suggest that antigen-specific TCR-related serum proteins may be elevated during an immune response to oral, environmental, or infectious stimuli.

B-cell activation in vitro by helper T cells specific to a protein region that is recognized both by T cells and by antibodies

This laboratory had previously mapped the regions of T and B cell recognition on sperm whale myoglobin (Mb). Mb has five regions (E1-E5) that are recognized by both T cells and B cells (i.e. antibodies, Abs) and an additional region (E6) that is recognized exclusively by T cells (i.e., TE6) and to which no Abs are detectable. The responses to the site are each under separate genetic control. Recently, we showed in an H-2d haplotype that TE6 cells preferentially activated Mb-primed B cells (BMb) that made Abs against sites within E3 and E4 on the same protein. In the present work, we established, from Mb-primed SJL mice, an E4-specific T cell line (TE4) by passage in vitro with synthetic peptide E4. At relatively low numbers, these T cells activated syngeneic BMb cells in vitro to produce anti-Mb Abs that recognized each of the antigenic sites within regions E1, E2, E3, E4 and E5. We confirmed the ability of TE4 to activate B cells that produce Abs against each of these regions by allowing TE4 to activate in vitro syngeneic B cells that had been primed with E1, E2, E3, E4 or E5. The helper activity of TE4 cells was dependent on the in vitro concentration of the challenge Ag (intact Mb or peptide E4). Thus, T cells against an epitope may provide help restricted to B cells that make Abs against selected antigenic sites or they may activate B cells that make Abs against all the antigenic sites of a protein. This might depend on the site-specificity of the T cell and/or on the host.

Intersite helper function of T cells specific for a protein epitope that is not recognized by antibodies

Humoral responses to a protein require T-B cell communication for B cell activation by T cells. Previous studies from this laboratory have mapped the T and B cell recognition sites (epitopes) on sperm-whale myoglobin (Mb) and several other proteins. It was found that, five of six regions on Mb recognized by T cells are also recognized by B cells (i.e. antibodies). There is, however, one region (E6) residing within Mb residues 61-77, that is recognized only by T cells and to which no antibody (Ab) responses are detectable. To investigate the function of this exclusive T cell epitope, we established, from E6-primed BALB/c mice, an E6-specific T cell line (T(e6)) which comprised Th2-type cells. These T cells provided help in vitro to B cells from Mb-primed BALB/c mice and activated them to produce anti-Mb Abs of the IgM (58.2%) and IgG (41.8%) isotypes. The helper activity of T(e6) cells was dependent on the concentration of the challenging Ag (intact Mb or peptide E6) in culture. Action of soluble factors released from E6-activated T(e6) cells on B(mb) cells led to low production of anti-Mb Abs, suggesting that activation of the B cells was more dependent on their contact with T cells. Mapping of the epitope recognition of the anti-Mb Abs produced in vitro by B(mb) cells on activation by T(e6) revealed that this activation was not general to all antigenic regions recognized by anti-Mb Abs in BALB/c mice. E6-specific T cells caused in vitro activation and differentiation of B(mb) cells into plasma cells that secreted anti-Mb Abs directed, in decreasing order, against the following Mb regions: E4 (107-120) > E3 (87 - 100) > E1 (10 - 22). Little or no Ab responses could be detected against peptides E2 (50 - 62), E5 (141 - 153) and E6 (61 - 77). With B cells of peptide-primed BALB/c mice, T(e6) cells activated strongly E4-, E3- or E1, and only very slightly E2- or E6-, primed B cells to secrete Abs against the correlate peptide, but failed completely to activate E5-primed B cells. The results show that a protein T cell epitope, to which no Abs are detectable, plays an active role in B cell responses against other epitopes within the same protein.

Detection of soluble T cell receptor-releasing cells by ELISPOT assay

A specific and sensitive enzyme-linked immunospot (ELISPOT) assay has been developed for the detection and enumeration of soluble T cell receptor (TCR)-releasing cells. Using this method, we readily detected at the single cell level the release of soluble TCR by living T lymphoma cells (MT-2 and HSB-2) but not by human B lymphoma cells (DAKIKI), mouse hepatoma cells (MH134) and dead MT-2. Furthermore, distinct spots in MT-2 cell culture were not visualized using several monoclonal antibodies against antigens unrelated to TCRs as a primary antibody. The specific and quantitative detection of soluble TCR-releasing cells using ELISPOT assay will certainly provide a valuable tool to better characterize soluble TCRs and their relationship to immune regulation and a number of diseases.

Immune modulation of biologic systems in renal somatic cells

The various theories discussed here suggest that somatic renal cells are susceptible to biologic modulation by the immune system independent of an inflammatory effect. (1) The mode of repression of type IV collagen synthesis by novel, soluble antigen-binding proteins, the down-regulation of class II MHC expression with interruption of antigen presentation to epithelia after selective gene regulation by antibody, and the diverse interactions of antibody with renal glomerular cells producing functional disturbances in endocytosis and permselectivity; (2) modification of surface-antigen composition; (3) alteration of matrix deposition, remodeling and composition; (4) biophysical perturbation of cytoskeletal and cell membrane components; (5) and lastly, alterations in cell adhesion through cell-surface alterations, all lend testimony to the richness of the signal transduction pathways in somatic cells. Although the preceding examples represent only a small fraction of those which may take place within the glomerular and tubular microenvironments, these paradigms may nevertheless serve as new models upon which one can consider the multitude of potential communications between disparate biologic systems that connect in complex organisms.

Revisiting and revising suppressor T cells

A great deal of experimental evidence supports the phenomenon of immunological suppression. The molecular mechanisms to explain the phenomenology have, however, remained controversial. In this review, the data are reinterpreted in light of the recent advances in the understanding of T-cell subsets, the cross-regulatory properties of lymphokines and the differential presentation capacities of different antigen-presenting cell types.

Immunoregulatory activity of the T-cell receptor alpha chain demonstrated by retroviral gene transfer

We have previously described an antigen-specific I-Ad-restricted T-cell hybridoma, A1.1, that constitutively releases an antigen-specific immunoregulatory activity into supernatants. Using retrovirally mediated gene transfer, we have found that transfer of the T-cell receptor alpha chain (TCR alpha) gene from A1.1 to a number of other T-cell hybridomas effectively transferred the ability to produce the activity. Gene transfer of the TCR beta chain (TCR beta), however, did not transfer this ability. The regulatory activity from cells expressing the A1.1 TCR alpha bound to and was eluted from an anti-TCR alpha monoclonal antibody and displayed fine antigenic specificity identical to that of supernatants from A1.1. The possibility that this activity represents a secreted form of the TCR alpha (as opposed to shed cell-surface TCR) was examined in BW1100 cells, lacking TCR alpha and TCR beta, which produced the antigen-specific activity after gene transfer of the A1.1 TCR alpha gene. The expression of the immunoregulatory activity in supernatants correlated with a direct antigen-binding activity as detected by ELISA, thus raising the possibility that antigen binding is relevant to the mechanism of action of the soluble TCR alpha. We discuss these observations and our earlier studies suggesting an immunoregulatory role for soluble TCR alpha.

T-cell-mediated activation of B cells

Antibody responses to protein antigens are dependent on helper T lymphocytes, which provide necessary growth and differentiation, inducing stimuli to antigen-specific B cells. Recent investigations have focused on the mechanisms of T-B interactions, and the nature of the T-cell-derived signals that are needed for activation and expansion of B cells.

T cell derived proteins from normal human sera and their relationship to T cell antigen binding molecules

We have used procedures which have been developed to isolate murine T cell antigen binding molecules (TABM) in order to isolate TABM from normal human sera. To begin purification, ammonium sulfate (NH4)2SO4 was added to human serum and precipitated protein was dissolved in low salt buffer and resolved by ion-exchange chromatography on carboxymethylcellulose (CM). The most strongly CM nonadherent fraction was absorbed with anti-human albumin and anti-human immunoglobulin (Ig) antibodies conjugated to Sepharose beads. The resulting nonadsorbed 110,000, 70,000 and 45,000 Mr polypeptides were reactive in ELISA with a rabbit antiserum produced against non-Ig, anti-specific molecules of rhesus monkeys. These proteins possess alpha mobility upon immunoelectrophoresis and represent 0.02 to 0.05% of total serum protein. In addition, these proteins are bound by an antiserum made against a synthetic peptide corresponding to the J region of the TcR beta chain. We have made R28, a rabbit antiserum against these serum proteins which binds specifically to tetanus-specific polypeptides obtained from the culture supernatant of human T cell lines specific for tetanus. This antiserum also binds to proteins isolated from T cell but not B cell lines, and T cell proteins are able to inhibit the binding of R28 to the human serum polypeptides. The results suggest that the proteins isolated from normal human sera are T cell antigen binding molecules.

Cognate interactions between helper T cells and B cells

The mechanism by which mammals produce an antibody response after exposure to antigen has intrigued biologists for over a hundred years. Here, Randolph Noelle and Charles Snow review some of the experimental findings since the early 1970s that have advanced understanding of the mechanisms operating during B-cell activation by thymus-dependent (TD) antigens. They also propose a model for B-cell activation that emphasizes the critical role played by direct cellular interactions between B cells and helper T(TH) cells and seek to place into perspective the role played by the membrane immunoglobulin (mlg) receptor in cognate responses.

The molecular basis of granuloma formation in schistosomiasis. IV. T cell-derived suppressor-inducer and suppressor-effector factor reactivities are regulated by a TCR beta chain analog

In Schistosomiasis mansoni, granulomatous modulation is mediated by antigenically and genetically restricted T suppressor-inducer and suppressor-effector cells and the soluble factors which they produce. The T suppressor-inducer factor (TsiF) is produced by an L3T4+, 14-30+ T cell. TsiF does not suppress directly, but induces the production of T-cell-derived suppressor-effector factor (TseF). TseF directly suppresses granuloma formation in vitro and in vivo. This study describes the molecular properties of TsiF. The factor is a nonimmunoglobulin heterodimer which can be separated into two component chains by dithiothreitol (DTT) reduction. The alpha chain imparts antigenic specificity and bears both the AgR and the epitope recognized by mAb 14-30 which characterizes T cells and factors of the Tsi phenotype. The beta chain imparts genetic restriction and bears both the I-J phenotypic marker and a T-cell receptor for Ag (TCR) V beta 8 determinant. These two chains can complement each other in vitro to reconstitute functional activity. The beta chain also determines the functional activity of T cell-derived suppressor factor (TsF). A beta chain, derived from TsiF, can complement the alpha chain derived from TsiF or TseF to reconstitute TsiF, but not TseF functional activity. Conversely the beta chain of TseF can reconstitute only TseF activity. These findings suggest that TsiF bears structural homologies to the TCR borne by Tsi cells and that the beta chain mediates the mode of functional interactions between TsFs and their target cells.