Influence of major histocompatibility complex haplotype on the mitogenic response of T cells to staphylococcal enterotoxin B

Abolition of aggregation of CH2 domain of human IgG1 when combining glycosylation and protein stabilization

The CH₂ domain is a critical element of the human Immunoglobulin G (IgG) constant region. Although the CH₂ domain is the least stable domain in IgG, it is also a promising scaffold candidate for developing novel therapeutic approaches. Recently, we succeeded in preparing glycosylated and non-glycosylated CH₂ domain in the host organism Pichia pastoris. Herein, we verified that glycosylation of the CH₂ domain decreased both, its tendency to aggregate and its immunogenicity in mice, suggesting that aggregation and immunogenicity are related. In addition, we have produced in P. pastoris a stabilized version of the CH₂ domain with and without glycan, and their propensity to aggregate evaluated. We found that stabilization alone significantly decreased the aggregation of the CH₂ domain. Moreover, the combination of glycosylation and stabilization completely suppressed its aggregation behavior. Since protein aggregation is related to immunogenicity, the combination of glycosylation and stabilization to eliminate the aggregation behavior of a protein could be a fruitful strategy to generate promising immunoglobulin scaffolds.

The protective function of invariant natural killer T cells in the relapse of experimental autoimmune uveoretinitis

Experimental autoimmune uveoretinitis (EAU) in mice provides a useful platform to study the pathogenesis and experimental therapeutics of human uveitis. One often used EAU model employs C57BL/6 (B6) mice sensitized with a peptide residue having 1 to 20 amino acids of human interphotoreceptor retinoid binding protein (hIRBP_1-20). The model using the B6 background has permitted a liberal use of genetically engineered strains and has provided insights for understanding uveoretinitis. However, this is usually acute/monophasic and does not represent human uveoretinitis that is characterized as a chronic/recurrent disease. Several chronic/recurrent EAU models have been developed; of these, we employed administration of staphylococcal enterotoxin B (SEB) for relapse in the present study, and found that recurrence was induced at day 24 after primary immunization, which is thought to be the convalescent phase. We reported the activation of invariant natural killer T (iNKT)-cells upon primary immunization of the EAU model mice with the ligand RCAI-56, which was found to mitigate the disease in our previous study. Here, we first attempted to ameliorate EAU in the relapse model using a preventive regimen by activating iNKT cells at the same time relapse induction (day 24) or in a regimen after 3 days of relapse induction (day 27). The preventive as well as post-inductive regimens were successful in reducing histopathological scores by inhibiting the Ag-specific Th17-biased response. Collectively, activation of iNKT cells may be useful to mitigate the relapse response of EAU induced with SEB.

Discordant rearrangement of primary and anamnestic CD8+ T cell responses to influenza A viral epitopes upon exposure to bacterial superantigens: Implications for prophylactic vaccination, heterosubtypic immunity and superinfections

Infection with (SAg)-producing bacteria may precede or follow infection with or vaccination against influenza A viruses (IAVs). However, how SAgs alter the breadth of IAV-specific CD8⁺ T cell (T_CD8) responses is unknown. Moreover, whether recall responses mediating heterosubtypic immunity to IAVs are manipulated by SAgs remains unexplored. We employed wild-type (WT) and mutant bacterial SAgs, SAg-sufficient/deficient Staphylococcus aureus strains, and WT, mouse-adapted and reassortant IAV strains in multiple in vivo settings to address the above questions. Contrary to the popular view that SAgs delete or anergize T cells, systemic administration of staphylococcal enterotoxin B (SEB) or Mycoplasma arthritidis mitogen before intraperitoneal IAV immunization enlarged the clonal size of ‘select’ IAV-specific T_CD8 and reshuffled the hierarchical pattern of primary T_CD8 responses. This was mechanistically linked to the TCR Vβ makeup of the impacted clones rather than their immunodominance status. Importantly, SAg-expanded T_CD8 retained their IFN-γ production and cognate cytolytic capacities. The enhancing effect of SEB on immunodominant T_CD8 was also evident in primary responses to vaccination with heat-inactivated and live attenuated IAV strains administered intramuscularly and intranasally, respectively. Interestingly, in prime-boost immunization settings, the outcome of SEB administration depended strictly upon the time point at which this SAg was introduced. Accordingly, SEB injection before priming raised CD127^highKLRG1^low memory precursor frequencies and augmented the anamnestic responses of SEB-binding T_CD8. By comparison, introducing SEB before boosting diminished recall responses to IAV-derived epitopes drastically and indiscriminately. This was accompanied by lower Ki67 and higher Fas, LAG-3 and PD-1 levels consistent with a pro-apoptotic and/or exhausted phenotype. Therefore, SAgs can have contrasting impacts on anti-IAV immunity depending on the naïve/memory status and the TCR composition of exposed T_CD8. Finally, local administration of SEB or infection with SEB-producing S. aureus enhanced pulmonary T_CD8 responses to IAV. Our findings have clear implications for superinfections and prophylactic vaccination.

Exposure to bacterial superantigens (SAgs) is often a consequence of infection with common Gram-positive bacteria causing septic and toxic shock or food poisoning. How SAgs affect the magnitude, breadth and quality of infection/vaccine-elicited CD8⁺ T cell (T_CD8) responses to respiratory viral pathogens, including influenza A viruses (IAVs), is far from clear. Also importantly, superinfections with IAVs and SAg-producing bacteria are serious clinical occurrences during seasonal and pandemic flu and require urgent attention. We demonstrate that two structurally distinct SAgs, including staphylococcal enterotoxin B (SEB), unexpectedly enhance primary T_CD8 responses to ‘select’ IAV-derived epitopes depending on the TCR makeup of the responding clones. Intriguingly, the timing of exposure to SEB dictates the outcome of prime-boost immunization. Seeing a SAg before priming raises memory precursor frequencies and augments anamnestic T_CD8 responses. Conversely, a SAg encounter before boosting renders T_CD8 prone to death or exhaustion and impedes recall responses, thus likely compromising heterosubtypic immunity to IAVs. Finally, local exposure to SEB increases the pulmonary response of immunodominant IAV-specific T_CD8. These findings shed new light on how bacterial infections and SAgs influence the effectiveness of anti-IAV T_CD8 responses, and have, as such, wide-ranging implications for preventative vaccination and infection control.

Bacterial Superantigens Expand and Activate, Rather than Delete or Incapacitate, Preexisting Antigen-Specific Memory CD8+ T Cells

Superantigens (SAgs) released by common Gram-positive bacterial pathogens have been reported to delete, anergize, or activate mouse T cells. However, little is known about their effects on preexisting memory CD8+ T cell (TCD8) pools. Furthermore, whether SAgs manipulate human memory TCD8 responses to cognate antigens is unknown. We used a human peripheral blood mononuclear cell culture system and a nontransgenic mouse model in which the impact of stimulation by two fundamentally distinct SAgs, staphylococcal enterotoxin B and Mycoplasma arthritidis mitogen, on influenza virus- and/or cytomegalovirus-specific memory TCD8 could be monitored. Bacterial SAgs surprisingly expanded antiviral memory TCD8 generated naturally through infection or artificially through vaccination. Mechanistically, this was a T cell-intrinsic and T cell receptor β-chain variable-dependent phenomenon. Importantly, SAg-expanded TCD8 displayed an effector memory phenotype and were capable of producing interferon-γ and destroying target cells ex vivo or in vivo. These findings have clear implications for antimicrobial defense and rational vaccine design.

Hock immunization: a humane alternative to mouse footpad injections

Footpad injection is a commonly used immunization method in mice. Being relatively easy to do with well-characterized lymphatic drainage, it has become a very useful immunization protocol to study local immune responses in draining lymph nodes. However, its disadvantages include use of only hind feet as a routine site of immunization since mice use their fore feet for food handling, and exacerbation of inflammation and swelling at the injection site leading to unrelieved pain and distress since feet are weight-bearing structures. With increasingly stringent Institutional guidelines for animal manipulations, there is increasing need for more humane protocols. A novel immunization protocol involving injection into the hock, the lateral tarsal region just above the ankle, a non-weight bearing structure draining to the same lymph node as the footpad, retains the advantages of footpad immunization without its drawbacks. This study, comparing immune responses between footpad and hock immunization in six different inbred mouse strains to two different protein antigens and a heat-killed bacterium, shows that hock immunization is a better alternative to footpad immunization, inducing comparable immune responses and being considerably more humane.

Roles of I-E molecule and CD28 costimulation in induction of suppression by staphylococcal enterotoxin B in vivo

Exposure to bacterial superantigens leads to the induction of a subsequent state of immune hyporesponsiveness. Using a transwell coculture system, a previous report demonstrated that splenocytes from staphylococcal enterotoxin B (SEB)-injected BALB/c mice secreted soluble mediators to suppress the proliferative response of naive syngeneic splenocytes to SEB stimulation. We show in the present study that, in contrast to the suppressive effect induced by SEB in BALB/c (H-2(d) haplotype), MRL(+/+), and MRL-lpr/lpr (H-2(k)) mice, SEB-primed splenocytes from I-E(-) strains such as B6, B10, A. BY (H-2(b)), and A.SW (H-2(s)) mice failed to inhibit the CD25 expression and the proliferative activity of their syngeneic naive responder splenocytes. Further results revealed that the SEB-primed cells from BALB/c, but not B6, mice inhibited the CD25 expression and proliferation of naive responder cells from either BALB/c or B6 mice, indicating the critical regulatory role of the effector cells. Unlike SEB, staphylococcal enterotoxin A induced profound suppression in both BALB/c and B6 mice. Moreover, the suppressive competence of SEB-primed splenocytes was diminished in CD28-deficient BALB/c mice. Taken together, our results indicate that when SEB is used as a stimulator in vivo, both the I-E molecule and CD28 costimulation are required for the induction of regulatory cells bearing suppressive activity.

Requirement of I-E molecule for thymocyte apoptosis induced by staphylococcal enterotoxin B in vivo

In vivo administration of bacterial superantigen staphylococcal enterotoxin B (SEB) to BALB/c mice led to thymus atrophy resulting from thymocyte apoptosis. In this study, we demonstrated that SEB induced a substantial reduction in thymocyte numbers in BALB/c, B10. D2 (H-2(d) haplotype), B10.BR, C3H/HeJ, C3H/HeN (H-2(k)), and (BALB/c x B6)F1 (H-2(dxb)), but caused little or no effect in I-E- strains such as B6, B10, A.BY (H-2(b)), and A.SW (H-2(s)) mice. Elimination of CD4(+)CD8(+) cells predominantly accounted for the thymocyte loss, although the numbers of other subpopulations may also be reduced. Thymocyte apoptosis was shown by an increase in the level of DNA fragmentation in BALB/c but not in B6 mice after SEB administration. Treatment with anti-I-Ed monoclonal antibody to BALB/c mice blocked SEB-induced thymocyte apoptosis when anti-I-Ad exerted less effect. In contrast to SEB, staphylococcal enterotoxin A led to comparable levels of thymus atrophy in BALB/c and B6 mice. Studies on the surface marker expression indicated that CD25 expression was upregulated on BALB/c mouse thymocytes but with only a moderate increase in B6 mice. The CD4(+)CD8(+) cells were the major (>90%) population that expressed elevated levels of CD25 in BALB/c mice. An increase in the expression of TCRalphabeta, CD3, and CD69 surface markers was also observed on thymocytes from BALB/c mice, but not from I-E- strains. The differential response of I-E+ and I-E- mice to SEB may be exploited as a model for the study of apoptosis in the thymus.

Host Genetic Determinants of Vaccine-Induced Eosinophilia During Respiratory Syncytial Virus Infection

In BALB/c mice, sensitization with the attachment protein (G) of respiratory syncytial virus (RSV) leads to CD4+ T cell-mediated lung eosinophilia during subsequent challenge with RSV. To determine the host genetic influences on this model of lung eosinophilia, we tested 15 different inbred mouse strains. Eosinophilia developed in all H-2d (BALB/c, DBA/2n, and B10.D2), but not in H-2k (CBA/Ca, CBA/J, C3H, BALB.K, or B10.BR) mouse strains. Among H-2b mice, 129 and BALB.B developed eosinophilia, whereas C57BL/6 and C57BL/10 did not. Testing first generation crosses between sensitive and resistant strains showed that eosinophilia developed in all H-2dxk (n = 5), irrespective of background genes, but not in H-2dxb (n = 2) mice. In vivo depletion of CD8+ T cells or IFN-γ rendered C57BL/6, but not BALB.K mice, susceptible to eosinophilia. Analysis of B10 recombinant mice showed that the Dd allele (in B10.A(5R) mice) prevented CD8+ T cell accumulation in the lung, resulting in intense lung eosinophilia. However, the Db allele (in B10.A(2R) and B10.A(4R) mice) supported CD8+ T cell expansion and prevented eosinophilia. Intracellular cytokine staining showed that lung eosinophilia correlated with reduced IFN-γ and increased IL-10 expression in lung T cells. These results are compatible with the unifying model that Th2 cells mediate the disease but can be inhibited by CD8+ T cells secreting IFN-γ. Our findings have important implications for the development of protective, nonpathogenic vaccines for RSV disease.

T-Cell epitope mapping the PorB protein of serogroup B Neisseria meningitidis in B10 congenic strains of mice

T-cell epitope mapping the meningococcal serotype 15 PorB protein performed in this study in three congenic strains of mice with B10 genetic background revealed at least three murine T-cell epitopes (55-72, 163-180, and 226-261), located in the highly conserved putative transmembrane regions of Neisserial porins. Proliferation assays with popliteal lymph node cells derived from mice immunized with the PorB protein or with synthetic 18-mer peptides showed that epitope 163-180 immunized only in the H-2d haplotype, epitope 55-72 could be presented by both H-2f and H-2s molecules, while the 226-261 region covered by three overlapping peptides could be efficiently recognized in context of all three MHC class II haplotypes studied. Inhibition experiments with blocking I-Aalpha- and I-Ealpha-specific mAb showed that peptide 163-180 was presented by I-Ad and peptide 244-261 was presented by both I-Af and I-As. In addition, evidence was obtained that peptide 226-243 was presented in context of H-2d or I-As haplotypes and peptide 55-72 was presented in context of I-Af and I-As loci. Finally, the Norwegian outer membrane vesicle vaccine, but not the purified PorB protein, could recall responses in mice immunized with synthetic peptides corresponding to the 226-261 region. Altogether, these results suggest that T-cell epitopes identified on the serotype 15 PorB protein, particularly those presented by several MHC class II molecules (e.g., 226-261), could have important implications for the development of meningococcal vaccines.

Allelic polymorphisms at the H-2A and HLA-DQ loci influence the response of murine lymphocytes to the Mycoplasma arthritidis superantigen MAM

Mycoplasma arthritidis, an agent of rodent arthritis, produces a potent superantigen (SAg), MAM. Previous work established that MAM is presented to T cells by murine H-2E or the homologous human HLA-DR molecules and that lymphocytes lacking a functional H-2E molecule fail to respond to MAM. Recently, more potent and purified preparations of MAM of known protein content have become available. This enabled us to more effectively compare the response of MAM with that of other SAgs by using lymphocytes from mice whose cells express different H-2A and HLA-DQ molecules. Here we demonstrate that cells from some H-2E-negative mouse strains respond to higher concentrations of MAM. By use of inbred, congenic, and recombinant mice, we show that these differences are, in fact, exercised at the level of the major histocompatibility complex (MHC) and that allelic polymorphisms at H-2A influence reactivity to MAM. In addition, polymorphisms at HLA-DQ, the human homolog of H-2A, also influence responsiveness to MAM. Cells expressing DQw6 (HLA-DQA1*0103 and DQBI*0601 chains) gave much higher responses to MAM than did cells expressing DQw8 (DQA1*0301 and DQB1*0302 chains). In fact, responses of lymphocytes expressing DQB1*0601 chains homozygously were as high as those observed for cells expressing a functional H-2E molecule. Murine lymphocytes responded less well to staphylococcal enterotoxin B (SEB) and SEA, but mouse cells expressing human MHC molecules gave much higher responses. The patterns of reactivity observed with cells expressing the various murine and human alleles differed for MAM, SEB, and SEA, suggesting that each of these SAgs interacts with different regions or residues on MHC molecules. It has been hypothesized that SAgs might play a role in susceptibility to autoimmune disease. Allelic polymorphisms at MHC loci might therefore influence susceptibility to autoimmune disease by affecting immunoreactivity to specific superantigens.

Human CD4 and human major histocompatibility complex class II (DQ6) transgenic mice: supersensitivity to superantigen-induced septic shock

Rodents are significantly less sensitive to enterotoxin-induced shock, and are thus not valid human disease models. Here, we describe a mouse strain carrying the human CD4 and human major histocompatibility complex (MHC) class II (DQ6) transgenes in an endogenous CD4- and CD8-deficient background. T lymphocytes from these animals react to minute amounts (10-100 times less than control mice) of staphylococcal enterotoxin B (SEB) in vitro, similar to concentrations to which human cells react. In vivo, these double-transgenic, double-knockout mice succumb to normally sublethal amounts of SEB. This sensitivity is not due to a biased T cell receptor V beta repertoire, increased T cell reactivity, or increased sensitivity to macrophage-derived cytokines. Rather, tumor necrosis factor (TNF)-alpha production by T cells and serum levels of TNF-alpha correlate precisely with the clinical syndrome, showing a biphasic T cell-dependent response. These data show that both human CD4 and MHC class II molecules can render mice supersensitive to superantigen-induced septic shock syndrome. This animal model mimics the progression of septic shock in man by transforming normally resistant mice into hypersensitive SEB responders, a trait that is characteristic of humans. Mice that have been humanized by exchanging autochthonous superantigen ligands by their human equivalents may be useful to decipher superantigen responses in vivo and to assess the pathogenesis of superantigen-associated diseases.

Stimulation of rat spleen cells by staphylococcal enterotoxins

There is much interest in staphylococcal enterotoxins as T cell mitogens in humans, mice and rabbits. Rat spleen cells were shown to proliferate in response to staphylococcal enterotoxins A and B and toxic shock syndrome toxin-1 at concentrations (5 to 500 ng ml-1) which also stimulate mouse spleen cells. The proliferative response to all these enterotoxins was inhibited by cyclosporin A, indicating the response to be predominantly that of T cells. These results indicate that the rat provides another convenient model for the analysis of T cell responses to enterotoxins.

Inhibition of allostimulated HLA-DQ and DP-specific T cells by staphylococcal enterotoxin A

Bacterial superantigens have two immunologically important features. They bind MHC class II molecules and stimulate T cells bearing certain V beta TCR phenotypes. Superantigens such as SEA, SEB, and TSST bind to each of the three HLA class II isotypes (DR, DQ, and DP). Allotypic variation seems to play an important role in superantigen binding to class II molecules, but the functional implications of these differences remain largely unknown. In the present investigation, we studied the effects of SEA, SEB, and TSST on allostimulation of HLA-DR-, DQ-, and DP-allospecific T-cell clones. To avoid direct stimulation of T-cell responses by the superantigens, SEA and/or SEB nonresponsive T-cell clones were selected. We show that SEA strongly inhibited DQ- and DP-specific T-cell responses. In contrast, SEB and TSST had only weak inhibitory effects. DR-specific T-cell responses were unaffected or only weakly inhibited by the superantigens tested. The inhibition appeared not to be due to induction of cytotoxicity or suppression of either T cells or EBV-LCLs by SEA. In conclusion, the bacterial superantigen SEA can block alloantigen-specific stimulation of T clones in vitro. These results suggest that SEA binds to certain MHC class II molecules in a way that prevents MHC-TCR interactions.

Induction of tumor necrosis factor and interleukin-1 by purified staphylococcal toxic shock syndrome toxin 1 requires the presence of both monocytes and T lymphocytes

Highly purified staphylococcal toxic shock syndrome toxin 1 (TSST-1) was tested for its ability to induce the cytokines tumor necrosis factor (TNF) and interleukin-1 (IL-1) from fractionated human peripheral blood mononuclear cells prepared from seven healthy donors. Highly purified monocytes alone or T lymphocytes alone did not produce TNF or IL-1 when incubated with TSST-1 at 37 degrees C for up to 72 h. However, the addition of 10 micrograms of TSST-1 per ml to a 1:1 mixture of monocytes and T cells resulted in significant TNF (predominantly TNF-alpha) and IL-1 beta production after 24 h at 37 degrees C. The nature of the monocyte/T-cell interaction did not appear to involve gamma interferon (IFN-gamma), since 10 micrograms of rabbit anti-IFN-gamma per ml did not neutralize TNF-alpha production after TSST-1 induction. Similarly, L243, a monoclonal antibody to HLA-DR which blocks TSST-1 binding to monocytes, did not inhibit TNF-alpha production following TSST-1 induction. However, direct contact between monocytes and T cells was required, since physical separation of cells in double-chamber culture wells abolished TNF-alpha secretion after TSST-1 stimulation. Furthermore, paraformaldehyde fixation of either monocytes or T cells prior to addition to viable T cells or monocytes, respectively, also abolished TNF-alpha secretion, suggesting that aside from cell contact, soluble factors were also involved. Our results suggest that cytokine production involves more than binding of TSST-1 to its receptor on monocytes alone and that cell contact with T cells and the release of a soluble factor(s) other than IFN-gamma may be essential for the induction of cytokines by this toxin.