Do holes in the T-cell repertoire have a center-surround regulatory structure? A rationale for the bifurcation of the Th1 and Th2 pathways of differentiation

Galectin-7 promotes proliferation and Th1/2 cells polarization toward Th1 in activated CD4+ T cells by inhibiting The TGFβ/Smad3 pathway

Galectin-7 (Gal-7) has been associated with cell proliferation and apoptosis. It is known that Gal-7 antagonises TGFβ-mediated effects in hepatocytes by interacting with Smad3. Previously, we have demonstrated that Gal-7 is related to CD4+ T cells responses; nevertheless, its effect and functional mechanism on CD4+ T cells responses remain unclear. The murine CD4+ T cells were respectively cultured with Gal-7, anti-CD3/CD28 mAbs, or with anti-CD3/CD28 mAbs & Gal-7. The effects of Gal-7 on proliferation and the phenotypic changes in CD4+ T cells were assessed by flow cytometry. The cytokines from CD4+ T cells were analysed by quantitative real-time PCR. Subcellular localisation and expression of Smad3 were determined by immunofluorescence staining and Western blot, respectively. Gal-7 enhanced the proliferation of activated CD4+ T cells in a dose- and β-galactoside-dependent manner. Additionally, Gal-7 treatment did not change the ratio of Th2 cells in activated CD4+ T cells, while it increased the ratio of Th1 cells. Gal-7 also induced activated CD4+ T cells to produce a higher level of IFN-γ and TNF-α and a lower level of IL-10. Moreover, Gal-7 treatment significantly accelerated nuclear export of Smad3 in activated CD4+ T cells. These results revealed a novel role of Gal-7 in promoting proliferation and Th1/2 cells polarization toward Th1 in activated CD4+ T cells by inhibiting the TGFβ/Smad3 pathway.

Toxoplasma gondii cathepsin proteases are undeveloped prominent vaccine antigens against toxoplasmosis

Background

Toxoplasma gondii, an obligate intracellular apicomplexan parasite, infects a wide range of warm-blooded animals including humans. T. gondii expresses five members of the C1 family of cysteine proteases, including cathepsin B-like (TgCPB) and cathepsin L-like (TgCPL) proteins. TgCPB is involved in ROP protein maturation and parasite invasion, whereas TgCPL contributes to proteolytic maturation of proTgM2AP and proTgMIC3. TgCPL is also associated with the residual body in the parasitophorous vacuole after cell division has occurred. Both of these proteases are potential therapeutic targets in T. gondii. The aim of this study was to investigate TgCPB and TgCPL for their potential as DNA vaccines against T. gondii.

Methods

Using bioinformatics approaches, we analyzed TgCPB and TgCPL proteins and identified several linear-B cell epitopes and potential Th-cell epitopes in them. Based on these results, we assembled two single-gene constructs (TgCPB and TgCPL) and a multi-gene construct (pTgCPB/TgCPL) with which to immunize BALB/c mice and test their effectiveness as DNA vaccines.

Results

TgCPB and TgCPL vaccines elicited strong humoral and cellular immune responses in mice, both of which were Th-1 cell mediated. In addition, all of the vaccines protected the mice against infection with virulent T. gondii RH tachyzoites, with the multi-gene vaccine (pTgCPB/TgCPL) providing the highest level of protection.

Conclusions

T. gondii CPB and CPL proteases are strong candidates for development as novel DNA vaccines.

Cytolytic CD4(+)-T-cell clones reactive to EBNA1 inhibit Epstein-Barr virus-induced B-cell proliferation

In the absence of immune surveillance, Epstein-Barr virus (EBV)-infected B cells generate neoplasms in vivo and transformed cell lines in vitro. In an in vitro system which modeled the first steps of in vivo immune control over posttransplant lymphoproliferative disease and lymphomas, our investigators previously demonstrated that memory CD4(+) T cells reactive to EBV were necessary and sufficient to prevent proliferation of B cells newly infected by EBV (S. Nikiforow et al., J. Virol. 75:3740-3752, 2001). Here, we show that three CD4(+)-T-cell clones reactive to the latent EBV antigen EBNA1 also prevent the proliferation of newly infected B cells from major histocompatibility complex (MHC) class II-matched donors, a crucial first step in the transformation process. EBNA1-reactive T-cell clones recognized B cells as early as 4 days after EBV infection through an HLA-DR-restricted interaction. They secreted Th1-type and Th2-type cytokines and lysed EBV-transformed established lymphoblastoid cell lines via a Fas/Fas ligand-dependent mechanism. Once specifically activated, they also caused bystander regression and bystander killing of non-MHC-matched EBV-infected B cells. Since EBNA1 is recognized by CD4(+) T cells from nearly all EBV-seropositive individuals and evades detection by CD8(+) T cells, EBNA1-reactive CD4(+) T cells may control de novo expansion of B cells following EBV infection in vivo. Thus, EBNA1-reactive CD4(+)-T-cell clones may find use as adoptive immunotherapy against EBV-related lymphoproliferative disease and many other EBV-associated tumors.

Immunological self/nonself discrimination: integration of self vs nonself during cognate T cell interactions with antigen-presenting cells

The hypothesis is presented that immunological integration of nonefficacious vs efficacious T cell antigen receptor (TCR) signals are foundational for self/nonself discrimination and that multiple integrative mechanisms are intrinsic to the molecular to molar organization of an adaptive immune response. These integrative mechanisms are proposed to adaptively regulate expression of costimulatory signals, such that foreign proteins are associated with the expression of costimulatory signals, whereas self-proteins are associated with the lack of costimulatory signaling. Overall, this model offers several unique contributions to the study of immunology. First, this model postulates that cognate TCR/major histocompatibility complex (MHC) interactions are sufficient to adaptively mediate immunological self/nonself discrimination. This model thereby offers a unique alternative to models that largely rely on innate immunity to prime immune discrimination. Second, the integrative model argues that the immune system can simultaneously reinforce self-tolerance and promote immunity to foreign organisms at the same time and in the same location. Many alternative models presume that pathogenic self-reactive T cells do not exist at the outset of an immune response against foreign agents. Third, the integrative model uniquely predicts relationships between immunodeficiency and autoimmune pathogenesis. Fourth, this model illustrates the regulatory advantages of cognate antigen presenting cell (APC) systems (i.e., T cell or B cell APC) compared to nonspecific APC. Cognate APC systems together with the respective clonotypic responders may comprise a fundamental "network" of lymphoid cells. Such networks would have clone-specific regulatory capabilities and may be central for immunological self/nonself discrimination. Fifth, this model provides an explanation for "infectious" tolerance without creating specialized subsets of "suppressor" or "regulatory" T cells. Each mature T cell retains the potential to reinforce tolerance or mediate immunity, depending on the specific antigenic cues present in the immediate environment.

Partial agonism elicits an enduring phase of T-cell-medicated antigen presentation

Previous studies have shown that the anti-CD4 mAb W3/25 strongly enhances T cell APC (T-APC) activity. In this study, single positive CD4+ and double negative (DN) (CD4-CD8-) T-helper cells specific for the 55-69 or 72-86 sequence of guinea pig (GP) myelin basic protein (GPMBP) were used to study CD4 regulation of T-APC activity. Clones were cultured with irradiated SPL and GPMBP or rat (R) MBP for 2-3 days, were propagated in IL-2 for another 1-3 days, were irradiated, and were used as T-APC. DN T cells specific for GP55-69 effectively presented GPMBP and were superior APC compared to other CD4+ T cells for presentation of this antigen. In contrast, DN T cells specific for the dominant encephalitogenic 72-86 determinant did not effectively present the agonist GPMBP but potently presented the partial agonist RMBP. The heightened APC activity of DN T cells reflected the lack of CD4 because the anti-CD4 mAb W3/25 promoted T-APC activity of CD4+ T cells to those levels expressed by DN T cells. Overall, T cells with potent reactivity to GPMBP or RMBP were subsequently unable to present that antigen, whereas T cells exhibiting partial or low antigen reactivities were highly effective APC for presentation of that antigen. The unrelated antigen conalbumin was presented by MBP-specific clones only when added to culture with a specific partial agonist. Together, these data indicate that partially agonistic MHC ligands promote prolonged expression of T-APC activity and that DN T cells may be specialized to mediate postactivational antigen presentation.