Expression of HLA-DR mRNA in T cells following activation is early and can precede DNA synthesis

A Low Frequency of IL-17-Producing CD8+ T-Cells Is Associated With Persistent Immune Activation in People Living With HIV Despite HAART-Induced Viral Suppression

Immune activation is the hallmark of HIV infection, even in patients with highly active anti-retroviral therapy (HAART)-induced viral suppression. A major cause of immune activation during HIV infection is the intestinal microbial translocation as a consequence, among other factors, of the decrease and/or dysfunction of interleukin (IL)-17-producing T-cells, due to their role promoting the integrity of the intestinal barrier. A population of IL-17-producing CD8⁺ T-cells (Tc17 cells), characterized by the expression of CD161, has been described, but its relation with the persistent immune activation in non-viremic people living with HIV (PLWH) on HAART is unclear. By flow cytometry, we characterized the activation phenotype (evaluated by the expression of HLA-DR and CD38) of circulating CD161-expressing CD8⁺ T-cells; in addition, we explored the functionality of polyclonally-stimulated Tc17 cells in PLWH under HAART-induced viral suppression, and in healthy individuals. Finally, we determined the association of Tc17 cells with the expression of cellular and soluble activation markers. Circulating CD161-expressing CD8⁺ T-cells were decreased in PLWH compared with healthy individuals, despite their similar basal activation state. After polyclonal stimulation, IL-17 production was higher in CD8⁺ T-cells co-expressing HLA-DR and CD38 in healthy individuals. In contrast, although PLWH had a higher frequency of HLA-DR⁺ CD38⁺ CD8⁺ T-cells after stimulation, they had a lower production of IL-17. Interferon (IFN)-γ-producing CD8⁺ T-cells (Tc1 cells) were increased in PLWH. The low Tc17 cells response was associated with a high expression of CD38 and programmed death 1 protein, high levels of soluble CD14 and the treatment duration. Finally, to explore potential immunomodulatory strategies, the in vitro effect of the anti-inflammatory agent sulfasalazine was assessed on Tc17 cells. Interestingly, a decreased inflammatory environment, death of activated CD8⁺ T-cells, and an increased frequency of Tc17 cells were observed with sulfasalazine treatment. Thus, our findings suggest that activated CD8⁺ T-cells have a marked capacity to produce IL-17 in healthy individuals, but not in PLWH, despite HAART. This dysfunction of Tc17 cells is associated with the persistent immune activation observed in these patients, and can be partially restored by anti-inflammatory agents.

Regulation and specificity of MHC2TA promoter usage in human primary T lymphocytes and cell line

Although activated human T cells express MHC class II antigens, the regulation of these antigens in T cells is poorly understood. This study focuses on the control of the MHC2TA gene in these cells. MHC2TA encodes the transcriptional master regulator of MHC class II, the class II trans-activator (CIITA). It has at least three distinct promoters (PI, PIII, and PIV), each active in an overlapping subset of cell types and directing a slightly different product. This report used highly purified blood T cells prepared by negative immunoselection to analyze CIITA. Real-time PCR analysis indicates that resting T cells do not express detectable CIITA transcript, while activated T cells express the PIII CIITA form. Transient transfection of activated blood T cells using wild-type and mutant PIII promoter-reporter constructs shows that two promoter elements, activation response element-1 (ARE-1) and ARE-2, are important for PIII function. cAMP response element binding protein, a known activator of gene expression in activated T cells, activates PIII in primary T cells. However, an intact ARE-2 site is not required for this activation, indicating that cAMP response element binding protein does not activate via this site. EMSAs indicate that an activating transcription factor/cAMP response element binding protein/cAMP response element modulator family member, but not phosphorylated cAMP response element binding protein-1, binds to ARE-2. ARE-2 also forms a complex with an unidentified protein. The ARE-2 binding protein is constitutively expressed in a DR(+) T cell line, reflecting differences between the DR(+) cell line and primary blood lymphocytes. These results show that MHC2TA PIII is induced in activated T lymphocytes, and that the induced binding of ARE-2 is a crucial step in this process.

B-cell antigens within normal and activated human T cells

In this study we compared cell surface staining for human peripheral blood lymphocyte (PBL) CD antigens by flow cytometry, with staining obtained following permeabilization of PBL using the Cytoperm method (Serotec). Six CD antigens (CD20, CD21, CD22, CD32, CD35 and major histocompatibility complex class II antigen) normally found on the surface of B cells, were also found to be expressed within T cells. We also showed, by immunoelectron microscopy, that these inappropriately expressed ('occult') CD antigens are located within cytoplasmic vesicles or within the rough endoplasmic reticulum. Following in vitro activation of T cells a distinct increase in expression of all of these cytoplasmic antigens was observed but staining at the cell surface was, by comparison, weak. We therefore propose that up-regulation of various B-cell CD antigens occurs within the cytoplasm of T cells following activation and that these antigens may be synthesized and released into the fluid-phase as soluble immunoregulatory molecules.

Class II transactivator (CIITA) is sufficient for the inducible expression of major histocompatibility complex class II genes

The class II transactivator (CIITA) has been shown to be required for major histocompatibility complex (MHC) class II gene expression in B cells and its deficiency is responsible for a hereditary MHC class II deficiency. Here we show that CIITA is also involved in the inducible expression of class II genes upon interferon gamma (IFN-gamma) treatment. The expression of CIITA is also inducible with IFN-gamma before the induction of MHC class II mRNA. In addition, CIITA mRNA expression does not require new protein synthesis, although new protein synthesis is necessary for the transcription of class II. This suggests that synthesis of new CIITA protein may be essential to induce class II gene expression. We also showed that the JAK1 protein tyrosine kinase activity is required to induce the expression of CIITA upon IFN-gamma stimulation. This finding indicates that CIITA is part of the signaling cascade from the IFN-gamma receptor to the activation of class II genes. In addition, the expression of CIITA is sufficient to activate class II genes in the absence of IFN-gamma stimulation suggesting that CIITA is the major regulatory factor for the inducible expression of class II genes. Together, these data suggest that CIITA is the IFN-inducible cycloheximide sensitive factor previously shown to be required for the induction of MHC class II gene expression.

Expression of activation markers on peripheral-blood lymphocytes following oral administration of Bacillus subtilis spores

This study was undertaken to assess the capability of Bacillus subtilis spores to modify the peripheral-blood lymphocyte (PBL) subsets or determine the de novo expression of activation markers. The data we obtained show that spores of B. subtilis are able to increase the expression of certain cell activation markers and that such activation is dose-dependent. In fact, doses of 2 x 10(9) spores did not give rise to changes in any of the parameters evaluated, while doses of 6 x 10(9) increased the HLA-DR antigen expression on T-lymphocytes. At the highest dosage used (12 x 10(9), B. subtilis spores caused the appearance of cells bearing the CD25 and CD71 activation markers. Therefore, such cell activation markers may prove useful for monitoring the activity of B. subtilis spores, and possibly of other immunomodulating agents, in the course of clinical research.

Reactivation of a major histocompatibility complex class II gene in mouse plasmacytoma cells and mouse T cells

Terminally differentiated plasma cells and mouse T cells do not express major histocompatibility complex (MHC) class II genes although class II gene expression is observed in pre-B and mature B cells as well as in activated human T cells. Transient heterokaryons were prepared and analyzed to investigate the mechanisms of inactivation of MHC class II gene in mouse plasmacytoma cells and mouse T cells. The endogenous MHC class II genes in both mouse plasmacytoma cells and mouse T cells can be reactivated by factors present in B cells. This reactivation of class II gene is also observed by fusion with a human T cell line which expresses MHC class II genes, but not with a class II negative human T cell line. It appears that the loss of MHC class II gene expression during the terminal differentiation of B cells or T cell lineage is due to absence of positive regulatory factor(s) necessary for class II transcription.

Post-transcriptional regulation of MHC class II expression in human T cells

Human T lymphocytes are among those cells which are cell surface class II- in the resting state, but can be induced to express class II following treatment with appropriate stimulators. Although resting T cells do not express detectable surface class II, cell surface class II can be detected on purified T cells as early as 30 min following stimulation with PHA and PMA, well before the initiation of DNA synthesis, and the percentage of positive cells gradually increases with time. One hypothesis explaining this very rapid surface expression of class II is that the genes can be regulated post-transcriptionally in T cells. To test this, we used nuclear run-on assays to measure the transcriptional rate of diverse class II genes in resting and activated T cells. Our results demonstrated that transcripts for DR, DP, and DQ could be detected in cells which were neither dividing nor transcribing mRNA for another marker of T cell activation, the IL-2 gene. Northern blot analysis demonstrated low to moderate steady-state levels of DR beta mRNA in these cells. Moreover, treatment of activated T cells with cycloheximide resulted in superinduction of class II for DR, DQ, and DP. These results suggest that resting T cells can transcribe mRNA for class II genes, but that they do not express the protein product on the cell surface in a detectable way until following activation. In addition, they suggest that there may be a protein factor which negatively influences class II levels in T cells. Thus, the regulation of class II in T cells is complex and involves post-transcriptional regulation, at least in part.

The control of class II expression on T cells is independent of the regulation of Tac and the induction of proliferation

In order to define the association between class II expression and other markers of T cell activation we tested the ability of various modes of stimulation to induce the expression of class II, Tac, and to stimulate proliferation. Stimulation of T cells with phytohaemagglutinin (PHA) in the presence of accessory cells strongly induced proliferation, Tac and the class II antigen DR. When purified T cells without accessory cells were stimulated with the phorbol ester, PdB, and the calcium ionophore, ionomycin, strong proliferation and Tac expression were induced, but only low levels of surface class II were observed. In contrast, stimulation of the same cells with PHA resulted in weak proliferation, strong Tac, but again low class II levels. The addition of PdB to the PHA increased the proliferative response, but did not affect Tac expression, which remained high, or class II expression, which remained low. Subsequent culture in conditioned medium of purified T cells which had been activated with either PdB and ionomycin or with PHA resulted in increased surface class II levels in both cases. Additional experiments suggested that neither IL-2, IL-4, nor interferon-gamma (IFN-gamma) alone was responsible. These results demonstrate that class II expression can be separated from the induction of proliferation and the upregulation of Tac and that the mode of T cell stimulation influences the resulting activation pathway. Furthermore, they suggest that the control of class II expression on T cells is more tightly regulated than it is on other cells.

Enhanced expression of HLA-class II molecules on activated human T lymphocytes following treatment with tumor necrosis factor alpha

Many factors induce or enhance expression of major histocompatibility complex class I and class II molecules on various cell types. Human T lymphocytes are class II negative in the resting state but show expression of class II molecules following activation. We analyzed the modulating capacity of the lymphokines recombinant interferon gamma (rIFN-gamma), interleukin-4 (IL-4), and recombinant tumor necrosis factor alpha (rTNF-alpha) on class II expression in subsets of alloactivated human T lymphocytes. The activated CD4+ T cells expressed all three class II isotypes (DR, DQ, and DP), whereas the cytotoxic CD8+ T-cell lines expressed DR and DP molecules but failed to bind DQ-specific monoclonal antibodies significantly. Treatment with rIFN-gamma and IL-4 had no effect on class II expression on any of the T-cell lines or clones, whereas rTNF-alpha enhanced class II expression in both subsets. rTNF-alpha could modulate expression of all three class II isotypes but, in principle, it appears only to affect ongoing class II synthesis as de novo synthesis of class II molecules with a resultant change in the class II phenotype from DR+ DQ- DP+ to DR+ DQ+ DP+ in the CD8+ T lymphocytes was not observed. No synergic effects of rINF-gamma and rTNF-alpha were observed; this results from the fact that activated T cells express few, if any, receptors of rIFN-gamma.