Evaluation of inducible costimulator/B7-related protein-1 as a therapeutic target in a murine model of allergic airway inflammation

Synovial inducible costimulator is correlated with severity in knee osteoarthritis

Osteoarthritis (OA) is a joint disease characterized by articular cartilage loss, which afflicts many people worldwide. Knowing the disease severity can improve the recovery rate of OA. Antibody array technology was utilized for protein expression profiling of synovial fluid from eight mild knee OA patients, eight severe knee OA patients and 16 healthy persons. Subsequently, 48 mild OA patients, 56 severe OA patients and 24 healthy controls were utilized for validation by ELISA. In the protein expression profiling, inducible costimulator (ICOS) levels were markedly higher in OA patients compared with those in the healthy population, and were significantly higher in severe OA than those in mild OA. Furthermore, ICOS levels were shown to be significantly correlated with WOMAC, MRI-MOAKS and MRI-UTE-T2* scores. The multivariate logistic regression analysis indicated that higher levels of ICOS could significantly increase the risk of severe OA. Synovial ICOS levels were positively correlated with the radiographic severity of OA. ICOS may represent a biomarker for predicting the OA severity and may be involved in the development and progression of knee OA.

Inducible Co-Stimulator (ICOS) in transplantation: A review

Prevention of T cell activation is one of the goals of successful organ and tissue transplantation. Blockade of T cell co-stimulation, particularly of the CD28:B7 interaction, has been shown to prolong graft survival. Inducible Co-Stimulator (ICOS) is the third member of the B7 family and here we review the literature on ICOS, its receptor (B7RP-1), and blockade of this pathway in transplant models. ICOS:B7RP-1 are a single receptor:ligand pair with a loss of function of either being implicated in some autoimmune diseases. ICOS has multiple functions, related to its constitutive expression on B cells and activated T cells. In in vitro transplant models, ICOS:B7RP-1 blockade has produced mixed results as to its ability to modulate lymphocyte proliferation. Several in vivo transplant models demonstrate varying degrees of success in prolonging graft survival. Timing and dose of treatment appear important, and combination with other immunosuppressive treatments may also be of benefit. As ICOS has multiple functions, it may be that the observed variable results are due to inadvertent inactivation of graft protective functions. If these barriers can be overcome, ICOS:B7RP-1 blockade could provide an important target for future immunosuppression regimens.

ICOS Costimulation Differentially Affects T Cells in Secondary Lymphoid Organs and Inflamed Tissues

B-cell interaction with follicular helper T cells and subsequent differentiation of B cells into high-affinity APCs normally takes place in secondary lymphoid organs. The costimulator ICOS plays a key role in this process and is therefore considered as an attractive target to modulate exaggerated B-cell responses in autoimmune or allergic diseases. Inflamed tissues were recently recognized as additional sites of active T-cell/B-cell interaction. To analyze whether ICOS costimulation is also important there, we employed a mouse airway inflammation model that allows direct comparison of immune reactions in the lung-draining lymph node and the lung tissue as well as assessment of the relative importance of dendritic cells versus B cells as APCs. In both organs, ICOS regulated the pool size of antigen-specific T and B cells and B-cell differentiation into germinal center(-like) cells but not into antibody-secreting cells. In the lymph node, lack of ICOS costimulation drastically reduced the frequency of T follicular helper cells but did not affect production of T-helper cell type 2 (Th2) cytokines. Vice versa in the lung tissue, ICOS did not change PD-1 expression on infiltrating T cells but regulated Th2 cytokine production, a process for which ICOS ligand expression on B cells was of particular importance. Taken together, the results of this study show that ICOS differentially regulates effector T cells in secondary lymphoid organs and inflamed tissues but that blockade of the ICOS pathway is suitable to target T cell-dependent B cell responses at both sites.

Targeting the ICOS/ICOS-L pathway in a mouse model of established allergic asthma disrupts T follicular helper cell responses and ameliorates disease

Background

Allergic asthma is characterized by chronic inflammation and remodelling of the airways, associated with dysregulated type 2 immune responses and allergen‐specific IgE. T follicular helper cells (T_FH) are crucial in T‐dependent B‐cell responses and have been implicated in allergic airway disease (AAD). T_FH, unlike other CD4⁺ T cells, are uniquely reliant on continuous ICOS signalling to maintain their phenotype after T‐cell priming; therefore, disrupting this signal can impair T_FH responses. However, the contribution of T_FH to disease during chronic aero‐allergen exposure and the therapeutic potential of targeting these cells have not been evaluated.

Methods

To establish AAD, female BALB/c mice were repeatedly exposed to house dust mite or Alternaria alternata three times a week for up to 5 weeks. To examine the impact of T_FH on AAD, mice were allergen exposed for 5 weeks and co‐administered anti‐ICOS Ligand‐targeted antibodies, three times a week for the last 2 weeks.

Results

T_FH were first observed in the lung‐draining lymph nodes and with further exposure were also found locally within the lungs. T_FH accumulated with sustained allergen exposure, alongside germinal centre (GC) B cells. Blockade of ICOS signalling after AAD establishment successfully depleted T_FH but did not affect the differentiation of other CD4⁺ T‐cell subsets. This reduced GC responses, allergen‐specific IgE, inflammation, pulmonary IL‐13 and airway hyper‐responsiveness.

Conclusions

T_FH are crucial in the regulation of AAD and the ICOS/ICOS‐L pathway could represent a novel therapeutic target in allergic asthma.

Novel treatments for systemic lupus erythematosus

There are many new therapeutic directions for the disease systemic lupus erythematosus (SLE). Despite this, the US Food and Drug Administration (FDA) has approved only one biological agent and it involves B cells, now thought to play a significant role in the pathogenesis of SLE. The name of the drug is belimumab, which is an agent that removes the B-cell cytokine called B lymphocyte stimulation factor (BLyS). Rituximab did not achieve its primary endpoints, even though the consensus is that it may be effective in some forms of SLE including renal disease. The anticytokine therapies against interleukin (IL)-6, IL-10, IL-17 and tumor necrosis factor (TNF) are effective in their own ways and phase II and III trials are in progress. Of particular interest to immunologists are the anti-interferon alpha and gamma drugs, which show promise in the animal models. Modulation of costimulatory molecules; specifically, the anti CD40, CTLA-***Ig and ICOS/B7RP blockade agents offer possibilities for the future using new pathways heretofore limited to rheumatoid arthritis. Finally, the use of tyrosine kinase inhibitors is another direction that has been successful in the inhibition of SLE in the murine model; early trials in human SLE have begun.

Differences in allergen-induced T cell activation between allergic asthma and rhinitis: Role of CD28, ICOS and CTLA-4

Background

Th2 cell activation and T regulatory cell (Treg) deficiency are key features of allergy. This applies for asthma and rhinitis. However with a same atopic background, some patients will develop rhinitis and asthma, whereas others will display rhinitis only. Co-receptors are pivotal in determining the type of T cell activation, but their role in allergic asthma and rhinitis has not been explored. Our objective was to assess whether allergen-induced T cell activation differs from allergic rhinitis to allergic rhinitis with asthma, and explore the role of ICOS, CD28 and CTLA-4.

Methods

T cell co-receptor and cytokine expressions were assessed by flow cytometry in PBMC from 18 house dust mite (HDM) allergic rhinitics (R), 18 HDM allergic rhinitics and asthmatics (AR), 13 non allergic asthmatics (A) and 20 controls, with or without anti-co-receptors antibodies.

Results

In asthmatics (A+AR), a constitutive decrease of CTLA-4+ and of CD4+CD25+Foxp3+ cells was found, with an increase of IFN-γ+ cells. In allergic subjects (R + AR), allergen stimulation induced CD28 together with IL-4 and IL-13, and decreased the proportion of CTLA-4+, IL-10+ and CD4+CD25+Foxp3+ cells. Anti-ICOS and anti-CD28 antibodies blocked allergen-induced IL-4 and IL-13. IL-13 production also involved CTLA-4.

Conclusions

T cell activation differs between allergic rhinitis and asthma. In asthma, a constitutive, co-receptor independent, Th1 activation and Treg deficiency is found. In allergic rhinitis, an allergen-induced Treg cell deficiency is seen, as well as an ICOS-, CD28- and CTLA-4-dependent Th2 activation. Allergic asthmatics display both characteristics.

Regulation of T cell response by blocking the ICOS signal with the B7RP-1-specific small antibody fragment isolated from human antibody phage library

A costimulatory signal is required for the full activation of T cells, in addition to the antigen-specific signal via the T cell receptor. The inducible costimulator, ICOS is one of the costimulatory molecules that play an essential role in this process, particularly in the expansion or the development of effector T cells. As blocking of the interaction between ICOS and its ligand, B7RP-1, suppresses the T cell response, it can be applied to the treatment of allograft rejection or autoimmune diseases. Here, we isolated four scFv clones that were specific to human B7RP-1 by biopanning a human antibody phage library. We found that three of these clones inhibited the interaction between ICOS-Fc and B7RP-1-Fc. These inhibitory clones not only recognized B7RP-1 molecules expressed on B cells, as assessed by FACS, but also exhibited inhibitory activity in a proliferation assay of T cells stimulated with anti-CD3 mAb and B7RP-1-Fc. Finally, the suppression effect of the scFv on the allogenic immune response was examined using a mixed lymphocyte reaction assay, which demonstrated a successful inhibition of the allogenic reaction, in spite of the high dose needed for complete inhibition (360 nM).

The role of costimulation in antibody deficiencies: ICOS and common variable immunodeficiency

SUMMARY

The identification of mutations in the inducible costimulator (ICOS) gene in nine patients with common variable immunodeficiency (CVID) was a major breakthrough. CVID is a complex, highly heterogeneous primary immunodeficiency disease, and the discovery of these mutations revealed a molecular basis. ICOS belongs to the CD28 family of costimulatory molecules and is expressed exclusively on activated T cells. It has at least three critical functions: germinal center formation, isotype class switching, and the development of memory B cells. The discovery of human ICOS deficiency showed that a monogenic disorder could account for the full spectrum of manifestations seen in childhood and adulthood-onset CVID, including autoimmune, inflammatory, and malignant disease complications, as well as recurrent infections. Moreover, this discovery showed that a disorder which had previously been perceived as a B-cell disease might in fact have its genetic origin in human T cells. In this article, we review the role of ICOS in the mammalian immune system and human disease, as well as the discovery and characteristics of patients with ICOS deficiency. Finally, we also discuss how these 'human knockouts' have contributed to our understanding of ICOS functions and have suggested potential avenues for using therapeutic ICOS manipulation to treat other diseases.

Increased expression of soluble inducible costimulator ligand (ICOSL) in patients with systemic lupus erythematosus

To investigate the level of costimulating molecules in systemic lupus erythematosus (SLE), we assessed the plasma concentrations of soluble forms of costimulatory molecules such as programmed death-1 (PD-1), B7-H1 (also called PD-L1 or CD274) and inducible costimulator ligand (ICOSL) in patients with SLE. Plasma concentrations of soluble PD-1, B7-H1 and ICOSL were measured by ELISA using plasma samples from 57 SLE patients with or without the active disease, 21 rheumatoid arthritis (RA) patients and 35 healthy subjects. We also evaluated surface ICOSL expression on B cells using flow cytometry to gain a better understanding of ICOSL expression. To compare the level of ICOSL mRNA expression, reverse transcriptase-polymerase chain reaction (RT-PCR) was performed using total RNA from peripheral blood mononuclear cells (PBMCs) isolated from eight healthy subjects and 11 patients with SLE. The concentration of plasma ICOSL was significantly higher in patients with SLE compared with healthy subjects ( P = 0.005). Plasma ICOSL concentrations in patients with active SLE were also significantly higher than those of either patients with inactive SLE or patients with RA ( P = 0.001, P = 0.015, respectively). Plasma ICOSL concentrations in patients with SLE correlated modestly with the SLE disease activity index score ( r = 0.298, P = 0.024). We also found a significant inverse correlation between the soluble ICOSL expression and the surface ICOSL expression on B cells ( r = −0.690, P = 0.001). However, ICOSL mRNA levels of patients with SLE were comparable with those of the control subjects. There was also no significant difference in plasma B7-H1 concentrations between groups, and plasma PD-1 was not detectable in any of the groups. The plasma concentration of soluble ICOSL might be correlated to the disease severity of lupus. The increased levels of ICOSL in active lupus suggest that this pathway is involved in the pathogenesis of SLE. The mechanism and physiological role of soluble ICOSL in the pathogenesis of SLE, however, remains to be investigated.

ICOS controls effector function but not trafficking receptor expression of kidney-infiltrating effector T cells in murine lupus

Renal pathology in systemic lupus erythematosus involves both autoantibody deposition and a cellular inflammatory response, both of which are mediated by effector CD4 T cells. MRL(lpr) mice spontaneously develop massive perivascular infiltrates, but the pathways that regulate the development, trafficking, and effector functions of kidney-infiltrating T cells are poorly defined. To address these questions, we first surveyed inflammatory chemokine protein levels in nephritic kidneys from lupus-prone MRL(lpr) mice. After identifying highly elevated levels of the CXCR3 ligand CXCL9, we found that kidney-infiltrating effectors are enriched for expression of CXCR3, as well as P-selectin ligand and ICOS. Using genetic ablation, we demonstrate that ICOS plays an essential role in the establishment of renal perivascular infiltrates, although a small number of infiltrating cells remain around the blood vessels. Interestingly, though IgG autoantibody production is substantially reduced in Icos(-/-) MRL(lpr) mice, the progression of immune complex glomerulonephritis is only modestly diminished and the production of inflammatory chemokines, such as CXCL9, remains high in the kidney. We find that Icos(-/-) effector cell numbers are only slightly reduced and these have normal expression of CXCR3 and P-selectin ligand with intact migration to CXCL9. However, they have impaired production of inflammatory cytokines and fail to show evidence of efficient proliferation in the kidney. Thus, while dispensable for acquisition of renal trafficking receptor expression, ICOS is strictly required for local inflammatory functions of autoreactive CD4 T cells in murine lupus.

Costimulation and allergic responses: immune and bioinformatic analyses

Asthma is a complex polygenic disease, the prevalence of which has been on the rise for last few decades. Defining the underpinnings of allergic immune responses and the factors predisposing to asthma are fundamental investigative challenges. T cell costimulatory pathways play critical roles in the pathogenesis of asthma. In this review, we analyze the current state of the art of T cell costimulation in allergic airway inflammation. Also, we discuss both immune and bioinformatic approaches as potential strategies for analyzing multiple costimulatory pathways relevant to asthma.

CD30 supports lung inflammation

The physiological functions of CD30 have not been fully elucidated. Here we show that in CD30-deficient mice (CD30(-/-)), lung inflammation is significantly diminished in the ovalbumin (OVA) model of airway hyperreactivity. In CD30(-/-) mice, the recruitment of eosinophils into the airways after OVA-aerosol challenge of OVA-primed mice was significantly diminished when compared with wild-type (w.t.) mice. IL-13 levels were also significantly reduced in CD30(-/-) mice while levels of IFN-gamma, IL-4, IL-5 and IgE in bronchoalveolar lavage fluid, lung tissue and serum were comparable to w.t. mice. Peribronchial lymph node cells from CD30(-/-) mice, re-stimulated in vitro with OVA, secreted significantly lower levels of IL-13 than those from w.t. mice, but showed normal proliferative response and other cytokine production. Exogenous IL-13 reconstituted airway recruitment of leukocytes in OVA-challenged CD3O(-/-) mice. Adoptive transfer to naive w.t. mice of in vitro OVA-re-stimulated spleen cells from CD30(-/-) mice failed to induce eosinophilic pulmonary inflammation in contrast to transfer of primed cells from w.t. mice. These results indicate that CD30 is a regulator of T(h)2 responses in the effector-memory phase and a regulator of IL-13 production in memory cells in the lung.

ICOS and B7 costimulatory molecule expression identifies activated cellular subsets in rheumatoid arthritis

To better define important cell subsets expressing activation markers in rheumatoid arthritis (RA), we compared selective lymphocyte and monocyte B7H1, B7H2, B7RP.1, B7RP.2, and inducible costimulatory molecule (ICOS) expression from normal peripheral blood (NL PB), RA PB, and RA synovial fluid (SF) by multicolor flow cytometry and immunohistochemistry. RA SF memory lymphocytes expressed B7RP.1 and B7RP.2, suggesting that T-cells may function as antigen presenting cells (APCs) in RA joints. We found similar results for ICOS expression. RA SF CD14+ monocytes also expressed B7RP.1 (an ICOS ligand) and the homologous ligand B7RP.2, identifying monocytes as potential mediators of antigen processing and lymphocyte activation in RA. Furthermore, we found an increased population of RA SF CD14+ monocytes expressing B7H1 and B7H2. [The FACS analysis was supported by immunohistochemistry, showing intense lymphocyte and APC (macrophages with dendritic morphology) ICOS staining in RA synovial tissue (ST). Overall, these results define elevated populations of memoryT-lymphocytes expressing proinflammatory B7 molecules in RA SF that either stimulate T cells through ICOS (via ICOS ligands B7RP.1 and B7RP.2), or down-regulate RA ST T-lymphocytes through B7H1 and B7H2.] Therefore, in the same joint, there may exist positive and negative influences on the inflammatory response, and perhaps, the negative signals dominate as joint inflammation resolves.

A negative regulatory role in mouse cardiac transplantation for a splice variant of CD80

BACKGROUND

Members of the B7 costimulatory protein family (CD80 and CD86) play a determining role in allograft rejection. Both CD80 and CD86 have naturally occurring splice variants whose roles in transplantation are unknown. Full length CD80 has two immunoglobulin (Ig)-like domains in the extracellular portion, IgC and IgV. In mouse, the isoform IgV-CD80 lacks the IgC-like domain. Here we analyzed the role of mouse IgV-CD80 in heart allograft rejection and search for equivalent splice variants in human.

METHODS

Mice made deficient for full-length CD80 but which retain expression of the shorter IgV-CD80 (CD80 mice) were used as donor or recipient of a heart allograft. Recipient animals were untreated or pretreated with alloantigen expressing cells and/or treated with CD80 and CTLA4 monoclonal antibodies (mAbs).

RESULTS

Recipients expressing IgV-CD80 but not full length CD80 exhibited a slight prolongation in survival of either wild-type (Wt) or CD80 grafts. More dramatically, CD80 animals pretreated with donor alloantigen exhibited permanent graft survival, whereas their Wt counterparts rejected their grafts with a median survival of 24 days. This prolonged survival was due to the expression of IgV-CD80 in recipients since treatment with CD80 mAb abrogated the beneficial effect observed. We identified and report here a similar isoform of CD80 from human cDNA encoding a putative soluble, IgV-containing protein.

CONCLUSIONS

IgV-CD80 bearing recipients show enhanced allograft survival especially after donor alloantigen pretreatment. This together with data from other species suggests that regulation delivered by splice variants of CD80 significantly modulates immunity and may be common across the species.

Roles of CD4+CD25+ T cells in the development of experimental murine allergic conjunctivitis

BACKGROUND

CD25+ regulatory T (T reg) cells play a suppressive role in experimental autoimmune uveoretinitis as well as experimental airway inflammation but their involvement in the development of allergic conjunctivitis (AC) remains unclear. We therefore investigated whether T reg cells play a role in the development of experimental AC (EC).

METHODS

BALB/c and C57BL/6 mice were actively immunized with ragweed (RW). The mice were treated with an anti-CD25 Ab (PC61) or control normal rat IgG (nrIgG) either 2 days prior to active immunization or during the induction phase (days 0, 2, 4, 6 and 8). Ten days after active immunization, the mice were challenged with RW-containing drops. Twenty-four hours after the challenge, the conjunctivas were harvested for histological analysis of eosinophil infiltration, and the spleens were harvested for cell culture for splenocyte transfer. Cultured splenocytes were transferred into syngeneic mice, and 4 days after the transfer, the recipient mice were challenged with RW. Twenty-four hours after the challenge, conjunctivas were collected for histological analysis.

RESULTS

Pretreatment with PC61 did not affect EC in either strain of mice; however, treatment with PC61 during the induction phase significantly suppressed EC in C57BL/6 mice. In contrast, transfer of RW-primed splenocytes from mice treated with PC61 induced EC that was significantly more severe regardless of strain and treatment protocol.

CONCLUSIONS

The finding that T reg cells play a suppressive role in the development of EC in splenocyte transfer experiments suggests that modulation of T reg cells may be a possible therapy for AC.

Co-stimulatory molecules as potential targets for therapeutic intervention in allergic airway disease

Airway inflammation is a characteristic feature of allergic asthma. Central to the initiation and progression of the inflammatory process are allergen-specific T lymphocytes that attract eosinophils, mast cells, and B cells to the airways by the secretion of specific cytokines. The direction of T cell responses is influenced by co-stimulatory signals that modulate the antigen-specific signal delivered by the T cell receptor. In addition to the prototypic co-stimulatory molecule, CD28, a number of newly identified co-stimulatory molecules and their ligands have now been characterized. Over the past 5 years, the role of these molecules in the pathophysiology of allergen-mediated sensitization and airway inflammation has been extensively studied in animal models of allergic asthma. The aim of this review is to provide a detailed overview on recent studies in mice and preliminary findings in man and to discuss the potential therapeutic and preventive treatment strategies offered by interactions with co-stimulatory molecules for patients with allergic airway diseases.

Expression and function of inducible co-stimulator in patients with systemic lupus erythematosus: possible involvement in excessive interferon-gamma and anti-double-stranded DNA antibody production

Inducible co-stimulator (ICOS) is the third member of the CD28/cytotoxic T-lymphocyte associated antigen-4 family and is involved in the proliferation and activation of T cells. A detailed functional analysis of ICOS on peripheral blood T cells from patients with systemic lupus erythematosus (SLE) has not yet been reported. In the present study we developed a fully human anti-human ICOS mAb (JTA009) with high avidity and investigated the immunopathological roles of ICOS in SLE. JTA009 exhibited higher avidity for ICOS than a previously reported mAb, namely SA12. Using JTA009, ICOS was detected in a substantial proportion of unstimulated peripheral blood T cells from both normal control individuals and patients with SLE. In CD4⁺CD45RO⁺ T cells from peripheral blood, the percentage of ICOS⁺ cells and mean fluorescence intensity with JTA009 were significantly higher in active SLE than in inactive SLE or in normal control individuals. JTA009 co-stimulated peripheral blood T cells in the presence of suboptimal concentrations of anti-CD3 mAb. Median values of [³H]thymidine incorporation were higher in SLE T cells with ICOS co-stimulation than in normal T cells, and the difference between inactive SLE patients and normal control individuals achieved statistical significance. ICOS co-stimulation significantly increased the production of IFN-γ, IL-4 and IL-10 in both SLE and normal T cells. IFN-γ in the culture supernatants of both active and inactive SLE T cells with ICOS co-stimulation was significantly higher than in normal control T cells. Finally, SLE T cells with ICOS co-stimulation selectively and significantly enhanced the production of IgG anti-double-stranded DNA antibodies by autologous B cells. These findings suggest that ICOS is involved in abnormal T cell activation in SLE, and that blockade of the interaction between ICOS and its receptor may have therapeutic value in the treatment of this intractable disease.

[T regulatory lymphocytes, atopy and asthma: a new concept in three dimensions]

BACKGROUND

Allergic inflammation is considered to be the result of a pattern of Th2 lymphocyte activation. However this inflammation, relevant for atopy and infiltration of affected tissues by eosinophils, is insufficient by itself to explain the clinical features of asthma. Several studies have demonstrated that Th2 type inflammation was also associated in asthma with a Th1 response, with production of gamma interferon. It has recently been shown that the regulatory T lymphocytes (Treg) which produce IL-10 and/or TGF-beta and induce tolerance are defective in allergic patients. In addition, these lymphocytes increase during specific immunotherapy. Their decrease could explain the Th2 activation found in atopic patients.

PERSPECTIVE

We review the potential importance of Treg cells in atopy and also asthma, and propose a concept whereby the allergic inflammatory response would not be due to a Th1/Th2 imbalance, but rather to a Treg deficiency progressively rising from normal to atopic, from atopy to asthma and from asthma to acute exacerbations.

CONCLUSION

Three dimensions of inflammation need therefore to be taken into account: Th1, Th2 and Treg.

CD28/CTLA-4--CD80/CD86 and ICOS--B7RP-1 costimulatory pathway in bronchial asthma

Costimulatory molecules are cell surface glycoproteins that can direct, modulate and fine-tune T-cell receptor signals. The B7-1/B7-2--CD28/CTLA-4 and ICOS-B7RP-1 pathway provides key second signals that can regulate the activation, inhibition and fine-tuning of T-lymphocyte responses. The expression of B7-1/B7-2--CD28/CTLA-4 molecules on clinical samples from patients with asthma have been well studied, and the results indicate that different extents of these molecules are expressed on the surface of various cells, and that the concentrations of soluble form of these molecules are elevated in the sera of patients with asthma. There is a burst of papers describing an important role for B7-1/B7-2--CD28/CTLA-4 pathway in the Th1/Th2 balance. Similarly, ICOS stimulates both Th1 and Th2 cytokine production but may have a preferential role in Th2 cell development. Moreover, The B7-1/B7-2-CD28/CTLA-4 and ICOS-B7RP-1 pathway has been suggested of being involved in the development of airway inflammation and airway hyperresponsiveness. Further study of the functions of the pathways within the CD28/CTLA-4--CD80/CD86 and ICOS--B7RP-1 superfamily individually and their interplay should provide insights into the pathogenesis of asthma, and has great therapeutic potential for treatment of asthma.

The interaction between ICOS and B7RP-1 is not required for the development of experimental murine allergic conjunctivitis

It is still unclear whether the interaction between inducible costimulator (ICOS) and its ligand, B7 related protein (B7RP)-1, is important for the development of allergic diseases. We investigated whether blocking the ICOS/B7RP-1 interaction affects the development of murine experimental allergic conjunctivitis (EC). EC was induced in Balb/c mice either by active immunization of ragweed (RW) or by transferring RW-primed splenocytes, followed by challenge with RW-containing eye drops. The mice were treated with anti-B7RP-1 antibody (Ab) or normal rat immunoglobulin G (IgG) during either the induction or effector phase. Regardless of the induction method or when the animals were treated, eosinophil infiltration into the conjunctiva was not affected by the anti-B7RP-1 Ab treatment. Splenocyte responses were not largely affected by this treatment. However, serum Ig levels were significantly reduced. These data suggest that blocking the ICOS/B7RP-1 in allergic diseases may not always be therapeutic.

Analysis of inducible costimulatory molecule participation during the induction and elicitation of granulomatous responses to mycobacterial and schistosomal antigens

The contribution of inducible costimulatory molecule (ICOS) to Th1 and Th2 cell-mediated immune responses was examined in well-defined pathogen antigen-elicited models of cell-mediated granuloma formation. Th1 and Th2 granulomas were respectively induced by intravenous challenge of CBA/J mice with Mycobacteria bovis purified protein derivative (PPD) or Schistosoma mansoni egg (SEA) antigen-coated beads. Effects of anti-ICOS blocking antibody on granulomas and lymphoid responses were assessed during elicitation and sensitization. Anti-ICOS treatment during the elicitation abrogated Th1- but not Th2-cell-mediated granuloma formation. Treatment during sensitization augmented SEA-bead granulomas and Th2 cytokines in lymphoid tissue. Anti-ICOS reduced the primary inflammatory response to PPD- but not to SEA-beads, despite comparable induction of ICOS-ligand and ICOS+ T cells. Treatment did not prevent early development of IFNgamma producing cells. Thus, post-activation effector Th1 activity was subject to ICOS blockade and chronic treatment caused diversion to Th2 dominance likely by eroding Th1 effector function or survival.

Increased expression of plasma and cell surface co-stimulatory molecules CTLA-4, CD28 and CD86 in adult patients with allergic asthma

The co-stimulatory interactions of the B7 family molecules CD80 and CD86 on antigen-presenting cells, together with their T cell counter receptors CD28 and cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), modulate T lymphocyte-mediated immune responses in a reciprocal manner. To investigate whether there is altered expression and the clinical significance of soluble co-stimulatory molecules in asthmatic patients, plasma concentrations of sCTLA-4, sCD28, sCD80 and sCD86 in 51 adult allergic asthmatic adults with or without steroid treatment, and 35 sex- and age-matched control subjects were measured by enzyme-linked immunosorbent assay (ELISA). Cell surface expression of CTLA-4 and CD28 on peripheral blood mononuclear cells (PBMC) were analysed by flow cytometry. Results showed that the plasma sCTLA-4 concentration was significantly higher in all asthmatic patients while sCD28 and sCD86 concentrations were significantly higher in steroid and non-steroid treated asthmatic patients, respectively, compared with control subjects (all P < 0.01). Significantly increased cell surface expression of CD28 but not CTLA-4 on PBMC was found in asthmatic patients compared with controls (P < 0.05). The plasma concentration and cell surface expression of CTLA-4 were found to exhibit positive and significant correlations with those of CD28 (both P < 0.05). Serum total IgE concentration correlated positively and significantly with sCTLA-4 and sCD28 concentrations in allergic asthmatic patients (both P < 0.05). The increased expression of these soluble co-stimulatory molecules may reflect the dysregulation of T cell activation, thereby contributing to the immunopathogenesis of allergic asthma.

B7RP-1 is not required for the generation of Th2 responses in a model of allergic airway inflammation but is essential for the induction of inhalation tolerance

The recently described ICOS-B7RP-1 costimulatory pathway has been implicated in the generation of effector Th2 responses and, hence, has become an attractive therapeutic target for allergic diseases. In the present study, we used B7RP-1-deficient mice to investigate the role of B7RP-1 in the generation and maintenance of Th2 responses in a model of mucosal allergic airway inflammation. We found that exposure of B7RP-1 knockout mice to aerosolized OVA in the context of GM-CSF leads to airway eosinophilic inflammation. This response was long lasting because rechallenge of mice with the same Ag recapitulated airway eosinophilia. Moreover, significant expression of T1/ST2 on T cells and production of Th2-affiliated cytokines (IL-5, IL-4, and IL-13) and Igs (IgE and IgG1) conclusively demonstrate the generation of a Th2 response in the absence of B7RP-1. In addition, expression of two major Th2-associated costimulatory molecules-CD28 and ICOS-indicates T cell activation in the absence of B7RP-1 signaling. Finally, B7RP-1 knockout mice are resistant to the induction of inhalation tolerance as indicated by the sustained eosinophilia in the lung and IL-5 production. In summary, our results demonstrate that in a model of mucosal allergic sensitization, the ICOS-B7RP-1 pathway is redundant for the generation of Th2 responses but essential for the induction of inhalation tolerance.

Allergen immunotherapy in the prevention of asthma

PURPOSE OF REVIEW

Asthma is a disease causing significant morbidity and mortality. In the recent past, there has been an explosion of pharmacotherapeutic options attempting to control the disease. Unfortunately, none of the current options offers the promise of prevention or a permanent cure. However, there appear to be exciting, new data emerging to support the hypothesis that the prevention or early treatment of allergic rhinitis, such as with the use of allergen immunotherapy, may help mitigate the severity of bronchial symptoms and even prevent the development of asthma. In this paper, we review recent research published proposing immunotherapy as a means of preventing the development of, or at least ameliorating, allergic asthma.

RECENT FINDINGS

There is evidence that the upper and lower airways may be considered a single unit, with the nasal and bronchial mucosa having features in common. Epidemiological, pathophysiological and clinical studies have shown that they can be affected by similar inflammatory triggers, with interconnected mechanisms amplifying the inflammatory cascade. Allergic rhinitis is interrelated to, and is a risk factor for, the development of asthma. An evidence-based review validates the successful use of allergen immunotherapy in treating allergic rhinitis and asthma. There is promising evidence advocating its use in the prevention of clinical asthma.

SUMMARY

This article explores current research pertaining to the use of immunomodulation, such as by using allergen immunotherapy, to ameliorate and prevent the development of allergic asthma.

The immunological synapse for B-cell memory: the role of the ICOS and its ligand for the longevity of humoral immunity

RECENT FINDINGS

The ICOS is one of the many costimulatory molecules of T cells. Recently, the authors discovered that the homozygous loss of the ICOS in humans presents as common variable immunodeficiency, the most prevalent treated primary immunodeficiency in man. Therefore, the ICOS is after CD40 and CD40-ligand deficiency the third costimulatory molecule for which a human disease has been described.

PURPOSE OF REVIEW

The description of ICOS deficiency made it necessary to review the vast amount of knowledge from experimental models in the light of a new clinical immunodeficiency phenotype. To this end, after introducing the ICOS and its ligand and comparing the murine and human 'knockout', the role of the ICOS in parasitic and viral infections, asthma, autoimmunity, transplantation immunology, and tumor surveillance will be discussed.

SUMMARY

The focus of this review is the interaction between the ICOS and its ligand, which is essential for T cell dependent B cell responses.

The role of ICOS and other costimulatory molecules in allergy and asthma

Activation and differentiation of T cells play a critical role in the pathogenesis of allergies and asthma. Upon encounter with specific antigen, naïve T helper precursor (ThP) cells become activated, an event that is regulated not only by engagement of the T cell receptor (TCR) with peptide presented in the context of MHC class II molecules, but also by a number of costimulatory signals. CD28 engagement by B7-1 and B7-2 on resting ThP cells provides a critical signal for initial cell cycle progression, interleukin-2 production and clonal expansion. However, in recent years, other related members of the immunoglobulin (Ig) family, such as inducible costimulatory molecules (ICOS) and the TNF receptor family members which include OX40, have also been demonstrated to play an important role in providing unique and complementary signals that regulate the outcome of immune responses. These positive costimulatory signals are counterbalanced by signals that dampen down immune responses and include CTLA-4, PD-1 and the recently described Ig superfamily members BTLA and TIM-3. This review discusses the role of these costimulatory signals and their potential involvement in the pathogenesis of asthma and allergic responses.

Continuous exposure to house dust mite elicits chronic airway inflammation and structural remodeling

It is now fully appreciated that asthma is a disease of a chronic nature resulting from intermittent or continued aeroallergen exposure leading to airway inflammation. To investigate responses to continuous antigen exposure, mice were exposed to either house dust mite extract (HDM) or ovalbumin intranasally for five consecutive days, followed by 2 days of rest, for up to seven consecutive weeks. Continuous exposure to HDM, unlike ovalbumin, elicited severe and persistent eosinophilic airway inflammation. Flow cytometric analysis demonstrated an accumulation of CD4+ lymphocytes in the lung with elevated expression of inducible costimulator a marker of T cell activation, and of T1/ST2, a marker of helper T Type 2 effector cells. We also detected increased and sustained production of helper T cell Type 2-associated cytokines by splenocytes of HDM-exposed mice on in vitro HDM recall. Histologic analysis of the lung showed evidence of airway remodeling in mice exposed to HDM, with goblet cell hyperplasia, collagen deposition, and peribronchial accumulation of contractile tissue. In addition, HDM-exposed mice demonstrated severe airway hyperreactivity to methacholine. Finally, these responses were studied for up to 9 weeks after cessation of HDM exposure. We observed that whereas airway inflammation resolved fully, the remodeling changes did not resolve and airway hyperreactivity resolved only partly.