Continuous exposure of mice to superantigenic toxins induces a high-level protracted expansion and an immunological memory in the toxin-reactive CD4+ T cells

A comparative study of colorimetric cell proliferation assays in immune cells

Cell proliferation assays are basic and essential techniques for assessing cellular function. Various colorimetric assays, such as MTT-, WST-1-, and resazurin-based assays, are available; however, studies directly comparing the suitability of each method for immune cell proliferation are scarce. Thus, we aimed to determine the best reagent and its optimal conditions based on variables such as cell number range, stimulation dose, kinetics, and compatibility with the cell division assay using CFSE fluorescence dye which is able to directly monitor divided cells by flow cytometry. In the absence of stimulation, MTT solubilized with SDS (MTT-SDS) and resazurin appeared to accurately reflect the cell numbers in a linear fashion. On the other hand, WST-1 exhibited a higher stimulation index following strong stimulation, whereas MTT-SDS and resazurin exhibited a better sensitivity to weak stimulation. A longer duration for stimulation did not necessarily increase sensitivity. CFSE staining revealed incremental cell division in response to anti-CD3 antibody stimulation in a dose-dependent manner. The cell numbers indirectly estimated from cell division profiles were consistent with the dose-response curve in the absorbance of MTT-SDS and resazurin. The absorbance does not increase before cell division, irrespective of T cell activation status, suggesting that these reagents reflect the cell number but not the cellular volume. Collectively, resazurin and MTT-SDS seem to be more reliable than others, and thus appear applicable in various conditions for the immune cell experiments.

Superantigenic Yersinia pseudotuberculosis induces the expression of granzymes and perforin by CD4+ T cells

Bacterial superantigens (SAgs) are immunostimulatory toxins that induce acute diseases mainly through the massive release of inflammatory cytokines. Yersinia pseudotuberculosis is the only Gram-negative bacterium known to produce a SAg (Y. pseudotuberculosis-derived mitogen [YPM]). This SAg binds major histocompatibility complex class II molecules on antigen-presenting cells and T cell receptors (TcR) bearing the variable region Vβ3, Vβ9, Vβ13.1, or Vβ13.2 (in humans) and Vβ7 or Vβ8 (in mice). We have previously shown that YPM exacerbates the virulence of Y. pseudotuberculosis in mice. With a view to understanding the mechanism of YPM's toxicity, we compared the immune response in BALB/c mice infected with a YPM-producing Y. pseudotuberculosis or the corresponding isogenic, SAg-deficient mutant. Five days after infection, we observed strong CD4(+) Vβ7(+) T cell expansion and marked interleukin-4 (IL-4) production in mice inoculated with SAg-producing Y. pseudotuberculosis. These phenomena were correlated with the activation of ypm gene transcription in liver and spleen. A transcriptomic analysis revealed that the presence of YPM also increased expression of granzyme and perforin genes in the host's liver and spleen. This expression was attributed to a CD4(+) T cell subset, rather than to natural killer T (NKT) cells that display a TcR with a Vβ region that is potentially recognized by YPM. Increased production of cytotoxic molecules was correlated with hepatotoxicity, as demonstrated by an increase in plasma alanine aminotransferase activity. Our results demonstrate that YPM activates a potentially hepatotoxic CD4(+) T cell population.

Emetic potentials of newly identified staphylococcal enterotoxin-like toxins

Staphylococcal enterotoxins (SEs) are a common causative agent of food poisoning. Recently, many new SE-like (SEl) toxins have been reported, although the role of SEls in food poisoning remains unclear. In this study, the emetic potentials of SElK, SElL, SElM, SElN, SElO, SElP, and SElQ were assessed using a monkey-feeding assay. All the SEls that were tested induced emetic reactions in monkeys at a dose of 100 μg/kg, although the numbers of affected monkeys were significantly smaller than the numbers that were affected after consuming SEA or SEB. This result suggests that these new SEs may play some role in staphylococcal food poisoning.

High affinity of interaction between superantigen and T cell receptor Vbeta molecules induces a high level and prolonged expansion of superantigen-reactive CD4+ T cells

In mice implanted with an osmotic pump filled with the superantigen (SAG) staphylococcal enterotoxin A (SEA), the Vβ3(+)CD4(+) T cells exhibited a high level of expansion whereas the Vβ11(+)CD4(+) T cells exhibited a mild level of expansion. In contrast, in mice implanted with an osmotic pump filled with SE-like type P (SElP, 78.1% homologous with SEA), the Vβ11(+)CD4(+) T cells exhibited a high level of expansion while the Vβ3(+)CD4(+) T cells exhibited a low level of expansion, suggesting that the level of the SAG-induced response is determined by the affinities between the TCR Vβ molecules and SAG. Analyses using several hybrids of SEA and SElP showed that residue 206 of SEA determines the response levels of Vβ3(+)CD4(+) and Vβ11(+)CD4(+) T cells both in vitro and in vivo. Analyses using the above-mentioned hybrids showed that the binding affinities between SEA and the Vβ3/Vβ11 β chains and between SEA-MHC class II-molecule complex and Vβ3(+)/Vβ11(+) CD4(+) T cells determines the response levels of the SAG-reactive T cells both in vitro and in vivo.

Role of opioid receptor like-1 receptor in modulation of endocrine, immunological, and behavioral responses to the T-cell superantigen staphylococcal enterotoxin A

Opioid receptor like-1 receptor (ORL(1)) is selective for orphaninFQ/nociceptin (OFQ/N), a peptide linked to stress. Since immunologic stimuli exert stressor-like effects, the neuroendocrine and behavioral effects of the T-cell superantigen staphylococcal enterotoxin A (SEA) were tested in ORL(1)(-/-) and ORL(1)(+/+) wildtype 129S6 mice. Within 2h of SEA challenge both genotypes showed elevated corticosterone, but only wildtypes were elevated after 4h, and had altered hypothalamic CRH mRNA. Although amygdaloid CRH and TNFalpha mRNA was increased by SEA, this did not vary with genotype. Interestingly, gustatory neophobia due to SEA challenge was augmented in ORL(1)(-/-) mice, although object neophobia tested 4days later was abrogated. These results suggest differential requirements for ORL(1) in the mediation of neuroimmune effects exerted at different times after an immune challenge.

Diagnosis of toxic shock syndrome by two different systems; clinical criteria and monitoring of TSST-1-reactive T cells

Two methods of TSS diagnosis were evaluated: comparison of symptoms with clinical criteria and monitoring for evidence of selective activation of Vbeta2(+) T cells by the causative toxin, TSS toxin-1 (TSST-1). Ten patients with acute and systemic febrile infections caused by Staphylococcus aureus were monitored for increase in TSST-1-reactive Vbeta2(+) T cells during their clinical courses. Nine of the ten patients were diagnosed with TSS based on evidence of selective activation of Vbeta2(+) T cells by TSST-1; however, clinical symptoms met the clinical criteria for TSS in only six of these nine patients. In the remaining patient, clinical symptoms met the clinical criteria, but selective activation of Vbeta2(+) T cells was not observed. Time taken to reach the diagnosis of TSS could be significantly shortened by utilizing the findings from tracing Vbeta2(+) T cells. In vitro studies showed that TSST-1- reactive T cells from TSS patients were anergic in the early phase of their illness. Examining selective activation of Vbeta2(+) T cells could be a useful tool to supplement clinical criteria for early diagnosis of TSS.

Superantigen-presentation by rat major histocompatibility complex class II molecules RT1.Bl and RT1.Dl

Rat major histocompatibility complex (MHC) class II molecules RT1.B(l) (DQ-like) and RT1.D(l) (DR-like) were cloned from the LEW strain using reverse transcription-polymerase chain reaction and expressed in mouse L929 cells. The transduced lines bound MHC class II-specific monoclonal antibodies in an MHC-isotype-specific manner and presented peptide antigens and superantigens to T-cell hybridomas. The T-cell-hybridomas responded well to all superantigens presented by human MHC class II, whereas the response varied considerably with rat MHC class II-transduced lines as presenters. The T-cell hybridomas responded to the pyrogenic superantigens Staphylococcus enterotoxin B (SEB), SEC1, SEC2 and SEC3 only at high concentrations with RT1.B(l)-transduced and RT1.D(l)-transduced cells as presenters. The same was true for streptococcal pyrogenic exotoxin A (SPEA), but this was presented only by RT1.B(l) and not by RT1.D(l). SPEC was recognized only if presented by human MHC class II. Presentation of Yersinia pseudotuberculosis superantigen (YPM) showed no MHC isotype preference, while Mycoplasma arthritidis superantigen (MAS or MAM) was presented by RT1.D(l) but not by RT1.B(l). Interestingly, and in contrast to RT1.B(l), the RT1.D(l) completely failed to present SEA and toxic shock syndrome toxin 1 even after transduction of invariant chain (CD74) or expression in other cell types such as the surface MHC class II-negative mouse B-cell lymphoma (M12.4.1.C3). We discuss the idea that a lack of SEA presentation may not be a general feature of RT1.D molecules but could be a consequence of RT1.D(l)beta-chain allele-specific substitutions (arginine 80 to lysine, asparagine 82 to aspartic acid) in the extremely conserved region flanking the Zn(2+)-binding histidine 81, which is crucial for high-affinity SEA-binding.

Long-term exposure to superantigen induces p27Kip1 and Bcl-2 expression in effector memory CD4+ T cells

The long-term exposure of mice to superantigen SEA using a mini-osmotic pump (SEA pump) induced a long-lasting expansion of Vbeta3+ CD4+ T cells with T helper (Th) 2 cell-type properties. Removal of the SEA pump 10 days after pump implantation did not significantly alter the level of Vbeta3+ CD4+ T cell expansion/maintenance. Furthermore, CFSE-labeled CD4+ T cells failed to divide when transferred to post-implantation day 15 mice. Thus, CD4+ T cells appeared to survive for at least 30 days in the absence of a sufficient amount of antigen to trigger cell division. STAT6 deficient mice, in which Th2 cell development is largely impaired, also exhibited a protracted cell expansion, similar to that observed in normal mice, suggesting that the Th2 cell property is dispensable for the maintenance of Vbeta3+ CD4+ T cell expansion. The expanded CD4+ T cells on post-implantation day 26 were arrested in the G0/G1 phase of the cell cycle and showed a lower level of cell division upon restimulation. The Cdk inhibitor p27(Kip1) was highly expressed, and Cdk2 was downregulated. Moreover, the CD4+ T cells were resistant to in vitro apoptosis induction in parallel with their level of Bcl-2 expression. Collectively, the Vbeta3+ CD4+ T cells appeared to develop into long-lived memory T cells with cell cycle arrest upon long-term exposure to SEA.

The complete genome sequence of Yersinia pseudotuberculosis IP31758, the causative agent of Far East scarlet-like fever

The first reported Far East scarlet-like fever (FESLF) epidemic swept the Pacific coastal region of Russia in the late 1950s. Symptoms of the severe infection included erythematous skin rash and desquamation, exanthema, hyperhemic tongue, and a toxic shock syndrome. The term FESLF was coined for the infection because it shares clinical presentations with scarlet fever caused by group A streptococci. The causative agent was later identified as Yersinia pseudotuberculosis, although the range of morbidities was vastly different from classical pseudotuberculosis symptoms. To understand the origin and emergence of the peculiar clinical features of FESLF, we have sequenced the genome of the FESLF-causing strain Y. pseudotuberculosis IP31758 and compared it with that of another Y. pseudotuberculosis strain, IP32953, which causes classical gastrointestinal symptoms. The unique gene pool of Y pseudotuberculosis IP31758 accounts for more than 260 strain-specific genes and introduces individual physiological capabilities and virulence determinants, with a significant proportion horizontally acquired that likely originated from Enterobacteriaceae and other soil-dwelling bacteria that persist in the same ecological niche. The mobile genome pool includes two novel plasmids phylogenetically unrelated to all currently reported Yersinia plasmids. An icm/dot type IVB secretion system, shared only with the intracellular persisting pathogens of the order Legionellales, was found on the larger plasmid and could contribute to scarlatinoid fever symptoms in patients due to the introduction of immunomodulatory and immunosuppressive capabilities. We determined the common and unique traits resulting from genome evolution and speciation within the genus Yersinia and drew a more accurate species border between Y. pseudotuberculosis and Y. pestis. In contrast to the lack of genetic diversity observed in the evolutionary young descending Y. pestis lineage, the population genetics of Y. pseudotuberculosis is more heterogenous. Both Y. pseudotuberculosis strains IP31758 and the previously sequenced Y. pseudotuberculosis strain IP32953 have evolved by the acquisition of specific plasmids and by the horizontal acquisition and incorporation of different genetic information into the chromosome, which all together or independently seems to potentially impact the phenotypic adaptation of these two strains.

CD4-dependent potentiation of a high molecular weight-melanoma-associated antigen-specific CTL response elicited in HLA-A2/Kb transgenic mice

The human high m.w.-melanoma-associated Ag (HMW-MAA) is an attractive target for the immunotherapy of melanoma, due to its relatively high expression in a high percentage of melanoma lesions and its restricted distribution in normal tissues. Active immunization with HMW-MAA mimics has been previously shown to induce a HMW-MAA-specific, T cell-dependent Ab response associated with an apparent clinically beneficial effect in advanced melanoma patients. Although T cells play an important role in controlling tumor growth, only limited information is available to date about the induction of HMW-MAA-specific CTL. In this report, we show that immunization of HLA-A2/K(b) transgenic mice with HMW-MAA cDNA-transfected syngeneic dendritic cells elicited a CD8(+) CTL response specific for HMW-MAA peptides with HLA-A2 Ag-binding motifs. The elicited CTL lysed HLA-A2(+)HMW-MAA(+) melanoma cells in vitro, and mouse HLA-A2/K(b) cells pulsed with HMW-MAA-derived peptides in vitro and in vivo. Although this CTL response could be generated in the absence of CD4(+) T cell help, harnessing CD4(+) T cell help in a noncognate Ag-specific manner with the polyclonal activator staphylococcal enterotoxin A augmented the CTL response. These results imply that dendritic cell-based immunization, in combination with CD4(+) T cell help, represents an effective strategy to implement T cell-based immunotherapy targeting HMW-MAA in patients with HMW-MAA-bearing tumors.

CD28 is required for induction and maintenance of immunological memory in toxin-reactive CD4+ T cells in vivo

We previously reported that Vbeta3+ CD4+ T cells maintained a protracted expansion, with the phenotypes of memory Th2 cells, for 30 days in C57BL/6 (B6) mice implanted with SEA-containing mini-osmotic pumps. In the present study, we followed the fate of Vbeta3+ CD4+ T cells in CD28-/- mice. Vbeta3+ CD4+ T cells increased to a degree similar to that of B6 Vbeta3+ CD4+ T cells until day 10 after implantation, then declined rapidly reaching the control level by 28 days. Remaining Vbeta3+ CD4+ T cells at that time did not exhibit memory phenotypes nor Th2-deviated responses. The rapid drop in Vbeta3+ CD4+ T cells in CD28-/- mice was attributable to upregulated induction of apoptosis owing to marginal inductions of Bcl-2 and Bcl-xL. Collectively, these data indicate CD28 to play critical roles in the generation and maintenance of SEA-reactive CD4+ T cells in vivo.

Natural killer T cells are required for the development of a superantigen-driven T helper type 2 immune response in mice

We show, here, that one single injection or weekly injections of staphylococcal enterotoxin B (SEB), starting in 1-day-old newborn mice, induced a powerful immune response with a T helper type 2 (Th2) pattern, as judged by the isotype and cytokine profile, with the production of large amounts of SEB-specific immunoglobulin G1 (IgG1), detectable levels of SEB-specific IgE and increased production of interleukin-4 by spleen cells. These protocols also induced an increase in the levels of total IgE in the serum. Memory of SEB was transferred to secondary recipients by using total spleen cells from primed animals. The secondary humoral response in transferred mice was diminished if spleen cells from SEB-treated mice were previously depleted of CD3+ or Vbeta8+ T cells or NK1.1+ cells. In vivo depletion of NK1.1+ cells in adult mice resulted in a marked reduction in the SEB-specific antibody response in both the primary and secondary immune responses. Additionally, purified NK1.1+ T cells were able to perform SEB-specific helper B-cell actions in vitro and in vivo. These results suggest that NK1.1+ T cells are required for the full development of humoral immunological memory, whilst making neonatal tolerance to SEB unachievable.

Deficiency of CD11b or CD11d Results in Reduced Staphylococcal Enterotoxin-Induced T Cell Response and T Cell Phenotypic Changes

The beta(2) integrin CD11a is involved in T cell-APC interactions, but the roles of CD11b, CD11c, and CD11d in such interactions have not been examined. To evaluate the roles of each CD11/CD18 integrin in T cell-APC interactions, we tested the ability of splenocytes of CD11-knockout (KO) mice to respond to staphylococcal enterotoxins (SEs), a commonly used superantigen. The defect in T cell proliferation with SEA was more severe in splenocytes from mice deficient in CD18, CD11b, or CD11d than in CD11a-deficient splenocytes, with a normal response in CD11c-deficient splenocytes. Mixing experiments showed that the defect of both CD11b-KO and CD11d-KO splenocytes was, unexpectedly, in T cells rather than in APC. Cytometric analysis failed to detect CD11b or CD11d on resting or activated T cells or on thymocytes of wild-type adult mice, nor did Abs directed to these integrins block responses in culture, suggesting that T cells educated in CD11b-KO or CD11d-KO mice were phenotypically altered. Consistent with this hypothesis, T cells from CD11b-KO and CD11d-KO splenocytes exhibited reduced intensity of CD3 and CD28 expression and decreased ratios of CD4/CD8 cells, and CD4(+) T cells were reduced among CD11b-KO and CD11d-KO thymocytes. CD11b and CD11d were coexpressed on a subset of early wild-type fetal thymocytes. We postulate that transient thymocyte expression of both CD11b and CD11d is nonredundantly required for normal thymocyte and T cell development, leading to phenotypic changes in T cells that result in the reduced response to SE stimulation.

Akt is a neutral amplifier for Th cell differentiation

Both CD28 and its relative, inducible costimulator (ICOS), have a binding motif for phosphatidylinositol 3-kinase (PI3K) in their cytoplasmic tail, and the binding of PI3K leads to activation of a serine/threonine kinase, Akt. The role of Akt in cytokine production and helper T (Th) cell differentiation remains obscure. In this study, we found that enforced expression of the constitutively active form (E40K) of Akt rendered CD4(+) T cells activated. Wild-type of Akt and E40K promoted Th1 cell differentiation in C57BL/6-derived and Th1-polarized BALB/c-derived CD4(+) T cells, while both promoted Th2 cell differentiation in BALB/c-derived and Th2-polarized C57BL/6 CD4(+) T cells. E40K also facilitated Th1 differentiation in CD4(+) T cells from IL-4-deficient mice with the BALB/c background. E40K up-regulated expression of NF-AT and c-Myb, which may be related to the augmentation of cytokine production by E40K. These findings indicate that the mechanism by which Akt augments cytokine production via CD28 and ICOS is Th cell type-specific and reflects the intracellular status affected by the cytokine milieu. We conclude that Akt is a neutral amplifier of T cell activation and Th differentiation.