Functional and biochemical characterization of a secreted I-J(+) suppressor factor that binds to immunoglobulin

Flavonoid biosynthesis in four Dendrobium species based on transcriptome sequencing and metabolite analysis

BACKGROUND

Dendrobium is a genus of plants used as traditional Chinese herbal medicines, with high economic and medicinal value.

METHODS AND RESULTS

To reveal the mechanism of flavonoid biosynthesis in Dendrobium, the metabolites and transcriptomes of four Dendrobium species (D. chrysotoxum, D. nobile, D. fimbriatum, and D. denneanum) were analyzed comprehensively. Ultra-high-performance liquid chromatography-tandem mass spectrometry analysis revealed ten flavonoid compounds in Dendrobium. In total, 100,096 unigenes were obtained from the transcript database of the four Dendrobium species. Among the identified differentially expressed genes, 51 were associated with flavonoid biosynthesis, and 670 differentially expressed transcription factors were predicted, including 194 MYB, 87 bHLH, and 100 WRKY family transcription factors, respectively. Transcriptome analysis showed that the expression levels of structural genes such as chalcone synthase (CHS), cinnamate-4-hydroxylase (C4H), and flavonoid 3'-hydroxylase (F3'H) were lower in D. chrysotoxum, D. nobile, and D. fimbriatum than those in D. denneanum, which may be the main reason for the low flavonoid contents in D. chrysotoxum, D. nobile, and D. fimbriatum.

CONCLUSIONS

The expression level of structural genes corresponded to the accumulation level of flavonols in the different Dendrobium species. The results deepen the understanding of the molecular mechanism of flavonoid biosynthesis in Dendrobium and provide novel insights into the synthesis and accumulation of flavonoids in Dendrobium.

A transforming growth factor beta-like immunosuppressive factor in immunoglobulin G-binding factor

Immunoglobulin G-binding factors (IgG-BF), which are produced by cells of the immune system, inhibit antibody production. In this paper, we show that transforming growth factor-beta (TGF-beta) suppresses secondary in vitro anti-sheep red blood cell responses of mouse splenocytes and lipopolysaccharide- or anti-IgM-stimulated mouse B cell responses in a way similar to, and with the same kinetics as, rodent IgG-BF. Moreover, the immunosuppressive activity of IgG-BF was totally neutralized by polyclonal and monoclonal anti-TGF-beta antibodies and it eluted with TGF-beta by gel exclusion chromatography, suggesting that a TGF-beta-like immunosuppressive factor is present in IgG-BF. We also show that TGF-beta behaves as an IgG-BF since it binds to insolubilized IgG, but not to insolubilized F(ab')2 or bovine serum albumin. Altogether, the data support the concept of a biological role for TGF-beta in the IgG-mediated negative feedback of antibody responses.

Immunological functions of mouse liver resident high density lymphocytes

Liver-derived high density lymphocytes (Matsunaga cells) have been detected as members of resident T cells in the mouse liver. In this study, we assessed the immunological functions of liver-derived high density lymphocytes of BALB/c mice in comparison with those derived from spleen and peripheral blood. Liver-derived high density lymphocytes proliferated in response to the syngeneic and allogeneic mixed lymphocyte reaction, as well as those derived from spleen and peripheral blood. The allo-activated cytotoxic T lymphocyte activity of liver-derived high density lymphocytes against PHA-blasts of C57BL/6 mice was lower than that of spleen- and peripheral blood-derived lymphocytes. The suppressor activity of syngeneic- or allo-activated high density lymphocytes of the liver, spleen, and the peripheral blood was assessed by measuring their suppressive effect on the proliferation or on the generation of allo-specific cytotoxic activity in allogeneic mixed lymphocyte reaction. The suppression was concentration-dependent and strongest in liver-derived lymphocytes.

A human suppressor T-cell factor that inhibits T-cell replication by interaction with the IgM-Fc receptor (CD7)

We have previously described the induction of human suppressor T cells from fresh peripheral blood lymphocytes of a kidney transplant recipient by in vitro stimulation with an autologous irradiated antidonor CTL line (EE-1) grown from a biopsy of the patient's own renal allograft. The induced T cells (designated TsEE) were shown to inhibit the in vitro generation of proliferative and cytotoxic responses of autologous T cells and nonautologous T cells that shared HLA-B7 with TsEE cells. Stimulation of TsEE cells by the autologous irradiated inducer line (EE-1) produced soluble factors (designated TsEEF) that similarly inhibited autologous and nonautologous T-cell responses to alloantigens and mitogens, but in a non-HLA-restricted manner. In this study, we examined the functional interaction of TsEEF with various cells surface receptors. TsEEF specifically inhibited the proliferation of stimulated and transformed T cells expressing CD7, a putative receptor for IgM-Fc (FcRmu). Blocking or capping of CD7-FcRmu determinants on responder T cells by pretreatment with IgM or anti-CD7 monoclonal antibodies (3A1, HuLy-m2) abrogated TsEEF activity. Conversely, pretreatment of T cells with TsEEF significantly reduced their binding of IgM and HuLy-m2. TsEEF was demonstrated not to be IgM or IgG, and its activity was not removed by preabsorption with IgM or IgG; however, its activity could be competitively inhibited by coculture with IgM. By cocapping experiments and studies utilizing CD7- (Hut-78) and CD7+ (HSB, Molt-4) T-cell lines. TsEEF activity did not appear to involve interactions with other T-cell or non-T-cell surface receptors. These findings suggest a novel role for FcRmu-CD7 T-cell surface receptors in binding certain soluble T-cell factors that result in the inhibition of T-cell replication.

T cell receptor-homologous mRNA from a suppressor T cell clone directs the synthesis of antigen-specific suppressive products

The LH8-105 T cell clone, obtained by radiation leukemia virus-induced transformation of hen egg-white lysozyme (HEL)-specific mouse suppressor T lymphocytes, constitutively releases in the culture supernatant products able to induce specific suppression of the immune response to HEL. LH8-105 cells rearrange and express the genes encoding the alpha and beta chains of the antigen-specific T cell receptor and display membrane T cell receptor structures. LH8-105 mRNA specific for the alpha and beta chains of the T cell receptor were positively selected on filter-bound cDNA encoding constant regions of alpha and beta chains, eluted and translated into Xenopus laevis oocytes. Translation products were then tested in vivo for specific suppression of the anti-HEL antibody response. LH8-105 culture supernatant and translation products of LH8-105 poly(A)+ RNA or a mixture of alpha and beta chain-homologous mRNA induce HEL-specific suppression whereas translation products of LH8-105 mRNA eluted from irrelevant DNA or unrecombined mRNA eluted from alpha and beta cDNA do not exert suppressive activity. These results indicate that alpha and beta chain-homologous mRNA expressed in LH8-105 cells direct the synthesis of molecules able to induce HEL-specific suppression.

Altered I-J phenotype in E alpha transgenic mice

One of the more intriguing puzzles in immunology is the genetic basis for control of murine T-cell I-J determinants. Molecules bearing I-J determinants (I-J molecules) play a role in information trafficking among immunocompetent cells, probably serving as self-recognition molecules that channel regulatory factors to their appropriate target cells. Although it is clear that I-J polymorphism is influenced by the major histocompatibility complex (MHC), molecular genetic studies provide evidence that an MHC gene does not encode I-J molecules. A possible explanation for this paradox is that I-J molecules are a set of non-MHC-encoded T cell receptors that are directly or indirectly selected for by self-MHC products. One key to resolving the genetic and molecular basis for control of I-J determinants is the identification of the MHC gene(s) involved. Herein, data are presented which show that E alpha transgenic mice express an altered I-J phenotype, providing clear evidence that I region class II genes influence I-J polymorphism. Although further study is required to resolve how class II genes mediate this effect, this is a major piece to the I-J puzzle.