Neil A. Williams

Immune modulation by the cholera-like enterotoxins: from adjuvant to therapeutic

Cholera toxin and its close relative, Escherichia coli heat-labile enterotoxin, are potent immunogens and mucosal adjuvants. The recent findings that their B subunits can promote tolerance highlights the complexity of their interactions with the immune system. Here, Neil Williams and colleagues review the mechanisms by which these molecules modulate leukocyte populations and seek to explain the paradox.

The genetic and immunopathological processes underlying collagen-induced arthritis

Animal models of rheumatoid arthritis (RA) have provided substantial insights into basic pathogenic mechanisms of chronic inflammatory arthritis and autoimmune disease in general. Of the variety of models reported, collagen‐induced arthritis (CIA) has been the most characterized in terms of both its pathogenesis and its underlying immunological basis. Collagen‐induced arthritis has also been the model of choice in terms of testing potential new therapeutic agents for the treatment of human RA. Nevertheless, the complex nature of the balance between T‐cell cytokines and the chronic inflammatory processes is only recently becoming clear. This review focuses on these developments, highlighting their implications for our understanding of RA and for the use of CIA as a suitable animal model.

Immunologically ignorant autoreactive T cells, epitope spreading and repertoire limitation

The factors that may cause antigen-presenting cells to alter the pattern of protein processing and presentation to autoreactive T cells, and thereby stimulate autoimmune disease, are currently under debate. In this article, Chris Elson and colleagues suggest that cytokines associated with T helper 1 (Th1) cells alter the processing of proteins and that this effect can be counteracted by Th2-associated cytokines.

Modulation of B-cell activation by the B subunit of Escherichia coli enterotoxin: receptor interaction up-regulates MHC class II, B7, CD40, CD25 and ICAM-1

The B subunits of cholera toxin (CtxB) and Escherichia coli heat‐labile enterotoxin (EtxB) are non‐toxic lectins that bind and cross‐link a ubiquitous cell glycolipid receptor, ganglioside GM1, and are recognized as potent mucosal and systemic immunogens. Here we examine the role of EtxB receptor occupancy in modulating the activation of B cells, in vitro, in primary lymphocyte cultures containing B and T cells. When 48‐hr spleen cell cultures containing EtxB were compared with those in the presence of a non‐receptor binding mutant, EtxB(G33D), a marked shift in the ratio of CD4+ T cells:B cells was noted. Evidence suggested that this was the result of either enhanced survival or proliferation of B cells associated with receptor occupancy by EtxB. Investigation revealed that EtxB induced only a minimal increase in proliferation above that of EtxB(G33D), in mixed cell cultures, and failed to induce any cell division of purified B cells or T cells. In contrast, receptor‐binding by EtxB markedly up‐regulated the expression of major histocompatability complex (MHC) class II, B7, intracellular adhesion molecule‐1 (ICAM‐1), CD40 and CD25 on the B‐cell surface. These results indicate that the polyclonal effects of EtxB on B cells are not associated with wide‐scale proliferation, but more likely with maintenance of B‐cell survival by activation of molecules essential for B‐cell differentiation. The findings also highlight the essential role of GM1‐interaction with EtxB in the regulation of lymphocyte responses.

The role of small intestinal antigen‐presenting cells in the induction of T‐cell reactivity to soluble protein antigens: association between aberrant presentation in the lamina propria and oral tolerance

The oral administration of soluble protein antigen results in profound immunological tolerance. However, the tissue location and function of antigen‐presenting cells (APC) that stimulate this response remain unclear. We have hypothesized that the properties of cells presenting antigen to naive T cells within the gut are involved, and therefore gut APC should stimulate T‐cell responses with different characteristics to those induced by other APC. To test this, we studied in vitro primary T‐cell responses following presentation of soluble protein antigen by cells from the Peyers patches (PPC) and lamina propria (LPC) of the murine small intestine and the spleen (SPLC). Each APC population stimulated antigen‐specific proliferative responses with similar anamnestic characteristics; however, analysis of the cytokines produced revealed marked differences. Whereas SPLC stimulated the balanced production of T‐helper type 1 (Th1) and Th2 cytokines, PPC induced a profile consistent with the provision of T‐cell help for IgA production. Interestingly, presentation of antigen by LPC stimulated high levels of interferon‐γ (IFN‐γ) and transforming growth factor‐β (TGF‐β) in the absence of other cytokines [interleukin‐2 (IL‐2), IL‐4, IL‐5]. Evidence from analysis of cell activation and division within the cultures suggested that this profile may result from the preferential activation of CD8+ T cells by LPC; however, the lack of conventional CD4+ T‐cell cytokines indicated a defect in the normal function of these cells. Adoptive transfer of antigen‐pulsed LPC to syngeneic animals abrogated the induction of delayed‐type hypersensitivity (DTH) responsiveness, which followed a subsequent conventional antigen challenge further suggesting a role for lamina propria APC in tolerance induction.

T Cell Memory Response to Pneumococcal Protein Antigens in an Area of High Pneumococcal Carriage and Disease

BACKGROUND Streptococcus pneumoniae is a leading cause of vaccine-preventable disease worldwide. Pneumococcal protein antigens are currently under study as components of potential vaccines that offer protection against multiple serotypes. We have therefore characterized T cell pneumococcal immunity acquired through asymptomatic carriage. METHODS Peripheral blood mononuclear cells from 40 healthy Gambian adults were stimulated with supernatants derived from S. pneumoniae strain (D39), 2 isogenic mutant strains lacking either pneumolysin or choline binding protein A, and recombinant pneumolysin. Immune responses were measured by cellular proliferation and by interleukin-10 (IL-10) and interferon-gamma (IFN-gamma) enzyme-linked immunosorbent spot and bioplex cytokine assays. Nasopharyngeal swabs were cultured to determine carriage rates. RESULTS S. pneumoniae nasopharyngeal carriage was detected in 60% of individuals. Both effector and resting (or central) CD4(+) T cell memory were frequently present to a range of pneumococcal antigens. However, the level of the effector memory response did not relate to current nasopharyngeal carriage. Pneumolysin was not immunodominant in these T cell responses but induced a distinct proinflammatory profile (high IFN-gamma, IL-12[p40], and L-17 levels and low IL-10 and IL-13 levels). CONCLUSIONS In this population, T cell-mediated immunological memory potentially capable of pathogen clearance and immune surveillance is common but is not associated with the absolute interruption of pneumococcal carriage. How this naturally acquired immune memory influences pneumococcal vaccine efficacy remains to be determined.

Evidence for Naturally Acquired T Cell-Mediated Mucosal Immunity to Neisseria meningitidis

Naturally acquired protective immunity against Neisseria meningitidis is thought to partially explain the disparity between the high levels of carriage in the human nasopharynx and the rare incidence of disease. To investigate this immunity to Neisseria meningitidis at the mucosal level, in vitro cellular responses to outer membrane vesicle preparations derived from this pathogen were examined using mononuclear cells from the palatine tonsils of adults and children. Characterization of these responses was achieved by depletion of CD45RA+, CD45RO+, and CD19+ populations and outer membrane vesicles derived from isogenic mutants expressing different serosubtypes of the major outer membrane protein, porin A (PorA), no PorA and membrane preparations from a mutant with no LPS (LpxA−). The magnitude of cellular proliferative responses against the outer membrane vesicles were strongly associated with age and were largely T cell mediated, involving both CD45RO+ and CD45RA+ T cell phenotypes. Responses were not dependent on LPS but consisted of both PorA cross-specific and non-PorA-dependent responses. Cellular immunity against Neisseria meningitidis was found to be frequently associated with systemic IgG Abs but was not associated with serum bactericidal Abs. For the first time our results demonstrate an age-associated acquisition of mucosal T effector/memory cell responses to Neisseria meningitidis. This mucosal cellular immunity can be present in the absence of serum bactericidal Abs, a classical marker of protective immunity.

Cell identification and isolation on the basis of cytokine secretion: A novel tool for investigating immune responses

Cell identification and isolation on the basis of cytokine secretion: A novel tool for investigating immune responses

Acquisition of pneumococci specific effector and regulatory Cd4+ T cells localising within human upper respiratory-tract mucosal lymphoid tissue.

The upper respiratory tract mucosa is the location for commensal Streptococcus (S.) pneumoniae colonization and therefore represents a major site of contact between host and bacteria. The CD4+ T cell response to pneumococcus is increasingly recognised as an important mediator of immunity that protects against invasive disease, with data suggesting a critical role for Th17 cells in mucosal clearance. By assessing CD4 T cell proliferative responses we demonstrate age-related sequestration of Th1 and Th17 CD4+ T cells reactive to pneumococcal protein antigens within mucosal lymphoid tissue. CD25hi T cell depletion and utilisation of pneumococcal specific MHCII tetramers revealed the presence of antigen specific Tregs that utilised CTLA-4 and PDL-1 surface molecules to suppress these responses. The balance between mucosal effector and regulatory CD4+ T cell immunity is likely to be critical to pneumococcal commensalism and the prevention of unwanted pathology associated with carriage. However, if dysregulated, such responses may render the host more susceptible to invasive pneumococcal infection and adversely affect the successful implementation of both polysaccharide-conjugate and novel protein-based pneumococcal vaccines.

Mutant Escherichia coli heat-labile toxin B subunit that separates toxoid-mediated signaling and immunomodulatory action from trafficking and delivery functions

ABSTRACT The homopentameric B-subunit components of Escherichia coli heat-labile enterotoxin (EtxB) and cholera toxin (CtxB) possess the capacity to enter mammalian cells and to activate cell-signaling events in leukocytes that modulate immune cell function. Both properties have been attributed to the ability of the B subunits to bind to GM1-ganglioside receptors, a ubiquitous glycosphingolipid found in the plasma membrane. Here we describe the properties of EtxB(H57S), a mutant B subunit with a His→Ser substitution at position 57. The mutant was found to be severely defective in inducing leukocyte signaling, as shown by failure to (i) trigger caspase 3-mediated CD8+-T-cell apoptosis, (ii) activate nuclear translocation of NF-κB in Jurkat T cells, (iii) induce a potent anti-B-subunit response in mice, or (iv) serve as a mucosal adjuvant. However, its GM1 binding, cellular uptake, and delivery functions remained intact. This was further validated by the finding that EtxB(H57S) was as effective as EtxB in delivering a conjugated model class I epitope into the major histocompatibility complex class I pathway of a dendritic cell line. These observations imply that GM1 binding alone is not sufficient to trigger the signaling events responsible for the potent immunomodulatory properties of EtxB. Moreover, they demonstrate that its signaling properties play no role in EtxB uptake and trafficking. Thus, EtxB(H57S) represents a novel tool for evaluating the complex cellular interactions and signaling events occurring after receptor interaction, as well as offering an alternative means of delivering attached peptides in the absence of the potent immunomodulatory signals induced by wild-type B subunits.