Pulmonary sarcoidosis is associated with high-level inducible co-stimulator (ICOS) expression on lung regulatory T cells--possible implications for the ICOS/ICOS-ligand axis in disease course and resolution

Sarcoidosis is a granulomatous inflammatory disorder of unknown aetiology. The increased frequency of activated lung CD4(+) T cells with a T helper type 1 (Th1) cytokine profile in sarcoidosis patients is accompanied by a reduced proportion and/or impaired function of regulatory T cells (Tregs ). Here we evaluated the expression of the inducible co-stimulator (ICOS) on lung and blood CD4(+) T cell subsets in sarcoidosis patients with different prognosis, by flow cytometry. Samples from the deep airways were obtained by bronchoalveolar lavage (BAL). We show that Tregs from the inflamed lung of sarcoidosis patients were characterized by a unique ICOS(high) phenotype. High-level ICOS expression was restricted to Tregs from the inflamed lung and was absent in blood Tregs of sarcoidosis patients as well as in lung and blood Tregs of healthy volunteers. In addition, lung Tregs exhibited increased ICOS expression compared to sarcoid-specific lung effector T cells. Strikingly, ICOS expression on Tregs was in particularly high in the lungs of Löfgren's syndrome (LS) patients who present with acute disease which often resolves spontaneously. Moreover, blood monocytes from LS patients revealed increased ICOS-L levels compared to healthy donors. Sarcoidosis was associated with a shift towards a non-classical monocyte phenotype and the ICOS-L(high) phenotype was restricted to this particular monocyte subset. We propose a potential implication of the ICOS/ICOS-L immune-regulatory axis in disease activity and resolution and suggest to evaluate further the suitability of ICOS as biomarker for the prognosis of sarcoidosis.

Impact of enzymatic tissue disintegration on the level of surface molecule expression and immune cell function

Immunological characterization of immune cells that reside in specific anatomic compartments often requires their isolation from the respective tissue on the basis of enzymatic tissue disintegration. Applying enzymatic digestion of primary splenocytes, we evaluated the impact of collagenase and dispase, two enzymes that are commonly used for the liberation of immune cells from tissues, on the detectability of 48 immunologically relevant surface molecules that are frequently used for flow cytometric identification, isolation, and characterization of immune cell subsets. Whereas collagenase treatment had only minor effects on surface expression of most molecules tested, dispase treatment considerably affected antibody-mediated detectability of the majority of surface markers in subsequent FACS analyses. This effect was long lasting and, in case of high-dose dispase treatment, evident for the majority of surface molecules even after 24 h of in vitro culture. Of note, high-dose dispase treatment not only affected surface expression of certain molecules but also impaired antigen-specific proliferation of CD4(+) and CD8(+) T cells. Together, our data indicate that enzymatic tissue disintegration can have profound effects on the expression of a variety of cell-surface molecules with direct consequences for phenotypic analysis, FACS- and MACS-based target cell isolation, and immune cell function in cell culture experiments.

CD4+ T cell mediated intestinal immunity: chronic inflammation versus immune regulation

BACKGROUND

Several studies have suggested that chronic inflammatory bowel disease may be a consequence of antigen specific recognition by appropriate T cells which expand and induce immunopathology.

AIMS

We wished to investigate whether autoreactive CD4+ T cells can initiate the disease on recognition of enterocyte specific antigens directly and if induction of mucosal tolerance occurs.

METHODS

Transgenic mice (VILLIN-HA) were generated that showed specific expression of haemagglutinin from influenza virus A exclusively in enterocytes of the intestinal epithelium. To investigate the impact of enterocyte specific haemagglutinin expression in an autoimmune environment, we mated VILLIN-HA mice with T cell receptor (TCR)-HA mice expressing an alpha/beta-TCR, which recognises an MHC class II restricted epitope of haemagglutinin, and analysed the HA specific T cells for induction of autoimmunity or tolerance.

RESULTS

In VILLIN-HAxTCR-HA mice, incomplete central deletion of HA specific lymphocytes occurred. Peripheral HA specific lymphocytes showed an activated phenotype and increased infiltration into the intestinal mucosa, but not into other organs of double transgenic mice. Enterocyte specific lamina propria lymphocytes showed a dose dependent proliferative response on antigen stimulation whereas the proliferative capacity of intraepithelial lymphocytes was reduced. Mucosal lymphocytes from VILLIN-HAxTCR-HA mice secreted lower amounts of interferon gamma and interleukin (IL)-2 but higher levels of tumour necrosis factor alpha, monocyte chemoattractant protein 1, and IL-6. Mucosal immune reactions were accompanied by broad changes in the gene expression profile with expression of proinflammatory genes, but strikingly also a remarkable set of genes discussed in the context of peripheral induction of regulatory T cells, including IL-10, Nrp-1, and Foxp3.

CONCLUSIONS

Enterocyte specific antigen expression is sufficient to trigger a specific CD4+ T cell response leading to mucosal infiltration. In our model, progression to overt clinical disease was counteracted most likely by induction of regulatory T cells.

The role of the bacterial membrane protein ActA in immunity and protection against Listeria monocytogenes

ActA, an essential virulence factor of Listeria monocytogenes, is an integral membrane protein that is required for intracellular motility, cell-to-cell spread, and rapid dissemination of the bacteria in the infected host. To reveal cytotoxic T cell responses against ActA we introduced a recombinant soluble form of ActA into the MHC class I-processing compartment of APC using a variant of listeriolysin mutated within its immunodominant MHC class I epitope. With this experimental system we demonstrate that T cells are induced against ActA during a sublethal infection with L. monocytogenes. However, adoptively transferred cytotoxic CD8+ T cells specific for ActA did not protect mice against a subsequent challenge with this pathogen. This was due to an inability of APC to present ActA by either MHC class I or class II molecules as long as ActA remained tethered to the surface of intracellular viable bacteria. ActA was only presented when L. monocytogenes were engineered to secrete ActA or when the bacteria were killed by antibiotics during the assay. These findings raise questions on the general use of membrane proteins of pathogens as candidates for subunit vaccines.

Efficient induction of cytotoxic CD8+ T cells against exogenous proteins: establishment and characterization of a T cell line specific for the membrane protein ActA of Listeria monocytogenes

The property of listeriolysin (LLO) to introduce soluble passenger proteins into the cytosol of antigen-presenting cells allows the induction of CD8+ cytotoxic T cells against such antigens. To overcome the potential problem of presentation of the immunodominant epitope LL091-99 by H-2Kd, a variant LLO92A was established in which Tyr 92 was replaced by Ala. Immunization of BALB/c mice with purified LLO92A failed to stimulate cytotoxic T cells specific for either the epitope LLO91-99 or for any other LLO-derived peptide. Injection of mixtures of purified LLO92A and soluble nucleoprotein (NP) of influenza virus into mice resulted in a strong cytotoxic T cell response exclusively directed against NP. The LLO92A variant was successfully used to generate, propagate and characterize a CD8 T cell line specific for the membrane-bound virulence factor ActA of Listeria monocytogenes. Interestingly, wildtype ActA bound to the surface of live L. monocytogenes was not presented by MHC class I molecules to the CD8+ T cell line.

Apoptosis of mouse dendritic cells is triggered by listeriolysin, the major virulence determinant of Listeria monocytogenes

Infection of a murine-spleen dendritic cell line by Listeria monocytogenes was found to induce cell death through apoptosis. To characterize the bacterial product(s) involved in induction of apoptosis, dendritic cells were infected with the L. monocytogenes EGD strain and several isogenic mutants deficient in the production of individual listerial virulence factors. The ability to induce cellular apoptosis was retained by all mutants tested, except the prfA and delta hly mutants, both of which are unable to produce listeriolysin. Apoptosis was also induced by purified listeriolysin suggesting that this protein directly induces apoptosis. Purified recombinant listeriolysins rendered either weakly haemolytic by a C-484 to S mutation, or nonhaemolytic by a W-491 to A mutation exhibited little or no capacity to induce apoptosis, indicating that both activities are associated within the same protein region. Treatment with purified listeriolysin or L. monocytogenes infection also triggers apoptosis in explanted bone-marrow dendritic cells. Thus invasion of dendritic cells by L. monocytogenes, which results in cell death, may play an important role in the pathogenesis of listerial infections by impairing immune responses, hindering bacterial clearance and promoting spread of the infection.

Time-dependent effects of oestradiol and progesterone on hypothalamic catecholamine turnover in ovariectomized rats

Long-term ovariectomized rats received a single injection of 20 micrograms oestradiol benzoate (OB) which reduced the serum levels of LH for at least 3 days. The inhibitory effects were accompanied by time-dependent alterations of noradrenaline and dopamine turnover rates in the mediobasal hypothalamus (MBH) and the preoptic-anterior hypothalamic brain area (POAH). Oestradiol markedly interfered with the time-dependent variations of noradrenaline and dopamine turnover seen in the MBH of untreated ovariectomized animals during daylight hours. In the POAH the turnover rate of noradrenaline decreased 2 days after priming with OB and then increased in the afternoon of day 3. The increase of noradrenaline turnover in the POAH was accompanied by a low afternoon turnover rate of dopamine in the MBH and by an increased sensitivity of the LH secretory system to progesterone. Dopamine and noradrenaline turnover involve a time element. While the negative feedback actions of oestradiol do not seem to be associated with changes in dopamine or noradrenaline turnover, the results support the view that the induction of LH afternoon surges depends upon an increase of stimulatory noradrenergic inputs to the POAH and a decrease of inhibitory dopaminergic inputs in the MBH.

Sex-specific effects of estradiol on hypothalamic noradrenaline turnover in gonadectomized rats

In long-term gonadectomized rats of either sex a single injection of estradiol-17 beta 3-benzoate acutely decreased the turnover rates of noradrenaline in the preoptic-anterior hypothalamic brain area (POAH) and reduced the serum concentrations of luteinizing hormone (LH). On the afternoon of day 3, between 72 and 78 h after estrogen priming, an increase of noradrenaline turnover was observed in female rats, whereas the turnover remained low in males. The increase of noradrenergic activity in female rat brain occurred at the time when LH release could be stimulated by progesterone. On the other hand, the low noradrenergic activity in the POAH of male rats correlated with the lack of stimulatory progesterone effects on LH secretion. The data indicate that estradiol induces a sex-specific increase of noradrenaline turnover in the POAH. This increase appears to be a prerequisite for the induction of LH surges.

Effects of oestradiol benzoate and progesterone on luteinizing hormone release and catecholamine turnover in the preoptic-hypothalamic brain area of ovariectomized rats

At noon, long-term (4-6 weeks) ovariectomized rats were exposed for 6-78 h to a single subcutaneous injection of oestradiol benzoate (20 micrograms) which significantly reduced the serum levels of LH over the whole time-interval investigated. The negative feedback action of oestradiol was accompanied by reduced turnover of both noradrenaline and dopamine in the preoptic-anterior hypothalamic brain area (POAH), but not in the mediobasal hypothalamus, 6, 68 and 72 h after administration of the hormone. Between 72 and 78 h after oestradiol-priming an afternoon increase of noradrenaline turnover was observed in the POAH. In rats primed with oestradiol benzoate for 72 h, short-term exposure (6 h) to progesterone (2.5 mg) induced a marked surge of serum LH and FSH in the late afternoon. In the POAH of these rats progesterone did not interfere with the afternoon increase of noradrenaline turnover induced by oestradiol-priming. However, it markedly increased the dopamine turnover rate of primed rats, thus reversing the inhibitory action of oestradiol benzoate on the dopaminergic system of the POAH. It is concluded that both the noradrenergic and the dopaminergic neurones of the POAH are involved in the negative and positive feedback actions of oestradiol and progesterone on LH and FSH release. The paper discusses whether the oestradiol-induced afternoon increase in noradrenaline turnover represents a prerequisite for the induction of LH surges by progesterone.