Synthesis of cytokines by eosinophils and their regulation

Therapeutic Potential of Hematopoietic Prostaglandin D2 Synthase in Allergic Inflammation

Worldwide, there is a rise in the prevalence of allergic diseases, and novel efficient therapeutic approaches are still needed to alleviate disease burden. Prostaglandin D₂ (PGD₂) has emerged as a central inflammatory lipid mediator associated with increased migration, activation and survival of leukocytes in various allergy-associated disorders. In the periphery, the hematopoietic PGD synthase (hPGDS) acts downstream of the arachidonic acid/COX pathway catalysing the isomerisation of PGH₂ to PGD₂, which makes it an interesting target to treat allergic inflammation. Although much effort has been put into developing efficient hPGDS inhibitors, no compound has made it to the market yet, which indicates that more light needs to be shed on potential PGD₂ sources and targets to determine which particular condition and patient will benefit most and thereby improve therapeutic efficacy. In this review, we want to revisit current knowledge about hPGDS function, expression in allergy-associated cell types and their contribution to PGD₂ levels as well as beneficial effects of hPGDS inhibition in allergic asthma, rhinitis, atopic dermatitis, food allergy, gastrointestinal allergic disorders and anaphylaxis.

Eosinophils in innate immunity: an evolving story

Eosinophils are innate immune leukocytes found in relatively low numbers within the blood. Terminal effector functions of eosinophils, deriving from their capacity to release their content of tissue-destructive cationic proteins, have historically been considered primary effector mechanisms against specific parasites, and are likewise implicated in tissue damage accompanying allergic responses such as asthma. However, the past decade has seen dramatic advancements in the field of eosinophil immunobiology, revealing eosinophils to also be key participants in many other facets of innate immunity, from bridging innate and adaptive immune responses to orchestrating tissue remodeling events. Here, we review the multifaceted functions of eosinophils in innate immunity that are currently known, and discuss new avenues in this evolving story.

Eosinophils and urticaria

Previously believed to have an exclusive role in the release of cytotoxic mediators in the defense against helminthic infections, eosinophils are now considered key players in inflammatory reaction and regulation of immune response. Through activation of a large variety of membrane receptors and production of various pharmacologically active mediators, eosinophils may exert a detrimental role in tissues in which they have been recruited and may contribute to the perennization of inflammatory processes. The crucial role of eosinophils has been documented in several eosinophilic skin diseases, such as hypereosinophilic syndrome and bullous pemphigoid, and the literature provides strong evidence for their role in urticaria. The aim of this article is to discuss the mechanisms of specific tissue recruitment of eosinophils, the factors of eosinophil activation, and the contribution of these cells to inflammation and immunoregulation in urticaria. Recent advances in the knowledge of eosinophils will certainly help toward developing new strategies for the management of antihistamines resistant to urticaria.

Allergen activates peripheral blood eosinophil nuclear factor-kappaB to generate granulocyte macrophage-colony stimulating factor, tumour necrosis factor-alpha and interleukin-8

BACKGROUND

Allergic inflammation is characterized by the influx and activation of eosinophils. Cytokines generated by both resident and infiltrating cells are responsible for the initiation and maintenance of this pathogenesis. This study focuses on allergen-induced activation of eosinophil NF-kappaB and generation of granulocyte macrophage-colony stimulating factor (GM-CSF), TNF-alpha, and IL-8.

METHODS

Peripheral blood eosinophils were enriched to >99.9% by Percoll gradient sedimentation and negative magnetic affinity chromatography. NF-kappaB activation by 10 microg/mL house dust mite (HDM) extract was demonstrated immunocytochemically using a monoclonal antibody against the active form of NF-kappaB (NF-kappaBa). The authenticity of NF-kappaB was confirmed by Western blot. Cytokine production was assessed both by immuno-staining of eosinophils and by assay of cytokines in the cell supernatant.

RESULTS

Activation of peripheral blood eosinophils from atopic, but not non-atopic, donors induced activation of NF-kappaB, which peaked at 4 h and was accompanied by a decline in IkappaB-alpha. The activation of authentic NF-kappaB was confirmed in gel shift assays. Supershift assays showed p65 to be the major subunit of eosinophil NF-kappaB. Immunofluorescent confocal microscopy demonstrated localization of NF-kappaBa to the nucleus. Following activation, cytokine immunoreactivity was seen in a fraction of the eosinophils and cytokines were released into the supernatant. The NF-kappaB inhibitors, calpain inhibitor 1 (10 microm), pentoxifylline (0.5 mm), pyrrolidine dithiocarbamate (PDTC, 10 microm) or gliotoxin (1 pg/mL) reduced the generation of GM-CSF, TNF-alpha and IL-8 in parallel with their inhibition of NF-kappaB.

CONCLUSIONS

HDM allergen activates human eosinophil NF-kappaB leading to the production of the cytokines GM-CSF, TNF-alpha and IL-8. We speculate that a role for eosinophil NF-kappaB-dependent cytokines is to act as an autocrine loop augmenting the survival of eosinophils in vivo.

Differential regulation by Seogak Jihwang-Tang on cytokines production in peripheral blood mononuclear cells from the cerebral infarction patients presenting with altered consciousness

Seogak Jihwang-Tang (SJT) has been widely used to treat patients suffering from cerebral infarction. However, very little scientific investigation has been carried out. We investigated the effect of SJT on the production of various cytokines using peripheral blood mononuclear cells from the cerebral infarction patients presenting with altered consciousness. The cytokines production was determined by enzyme-linked immunosorbent assay. The amount of IL-4, IL-10 and TGF-beta1 in culture supernatant significantly increased in the SJT, lipopolysaccharide (LPS) or PHA-treated cells compared to unstimulated cells (P < 0.05). We also showed that increased IL-4 and IL-10 levels by LPS or phytohaemagglutinin (PHA) were significantly inhibited by SJT in a dose-dependent manner. Maximal inhibition rate of IL-4 and IL-10 production by SJT was 45.6 +/- 3.3% and 61 +/- 4.7% for LPS-stimulated cells and 27.3 +/- 1.2% and 83.6 +/- 2% for PHA-stimulated cells, respectively (P < 0.05). On the other hand, SJT significantly increased the LPS or PHA-induced TGF-beta1 production (P < 0.05). These data suggest that SJT has a regulatory effect on the cytokines production, which might explain its beneficial effect in the treatment of cerebral infarction.

The effect of Jeo Dang-Tang on cytokines production in the patients with cerebral infarction

The herbal formulation "Jeo Dang-Tang" (JDT) has long been used for various cerebrovascular diseases. However, very little has scientific investigation been carried out. The aim of the present study is to investigate the effect of JDT on the production of various cytokines in the patients with cerebral infarction (CI). Peripheral blood mononuclear cells (PBMC) obtained from the patients with CI were cultured for 24h in the presence or absence of lipopolysaccharide (LPS) or phytohemagglutinin (PHA). The amount of interleukin (IL)-4, IL-10 and transforming growth factor (TGF)-1beta, in culture supernatant, was significantly increased in the JDT, LPS or PHA treated cells compared to unstimulated cells (P < 0.05). We also show that increased IL-4, and IL-10 level by LPS or PHA was significantly inhibited by JDT in a dose-dependent manner. Maximal inhibition rate of IL-4 and IL-10 production by JDT was 45 +/- 2% and 51 +/- 5% for LPS-stimulated cell and 41.5 +/- 3% and 70.8 +/- 2% for PHA-stimulated cells, respectively (P < 0.05). On the other hand, JDT significantly increased the LPS or PHA-induced TGF-beta1 production (P < 0.05). These data suggest that JDT has a regulatory effect on the cytokines production, which might explain its beneficial effect in the treatment of CI.

Cytokine expression during allergen-induced late nasal responses: IL-4 and IL-5 mRNA is expressed early (at 6 h) predominantly by eosinophils

The production of TH2-type cytokines [interleukin-4 (IL-4) and IL-5] and tissue eosinophilia are characteristic features of allergic diseases. It was previously reported that at 24 h after allergen provocation, CD3+ T-lymphocytes were the principal cell source of IL-4 and IL-5 mRNA transcripts in both atopic asthma and rhinitis. To investigate whether IL-4 and IL-5 mRNA are expressed earlier during late nasal responses and if so, which cell(s) are responsible. Nasal biopsies were obtained at 6 h after nasal allergen challenge and following a control challenge with the allergen diluent. Sections were immunostained for T-lymphocytes (CD3+, CD4+) and eosinophils (EG2+). In situ hybridization was used to detect the number of cells expressing messenger RNA (mRNA) for IL-4 and IL-5. In patients with allergic rhinitis, eosinophils (EG2+ cells P = 0. 006) but not T- cells (CD3+ cells) increased in the nasal mucosa at 6 h after allergen challenge. The number of cells expressing IL-4 mRNA (P = 0.01) and IL-5 mRNA (P = 0.05) also increased at 6 h. Co-localization studies showed that 76% of IL-4 mRNA+ cells and 77% of IL-5 mRNA+ cells were eosinophils, whereas at this time point, T-cells and mast cells accounted for </=5% of mRNA expression; the identity of the remaining 20% of IL-4 and IL-5 mRNA+ cells was not determined. By use of immunohistology, cytokine protein expression at 6 h was confirmed for IL-4 but not for IL-5. No increases in T-cells, eosinophils or cytokine expression were detected in non-atopic subjects. Eosinophils represent an early source of IL-4 which may contribute to TH2-type responses during late nasal responses and ongoing allergic rhinitis.

Human eosinophil-lymphocyte interactions

While the eosinophil's effector functions clearly can contribute to the pathogenesis of allergic diseases, the evolutionary benefit to having eosinophils as a distinct class of leukocyte is not clear, especially if one must reconsider the nominally beneficial role of eosinophils in parasite host defense, Eosinophils are equipped to respond to lymphocytes and their cytokines (and not solely the eosinophil growth factor cytokines), but the functional consequences of such eosinophil responses need to be defined. Conversely, eosinophils, as antigen-presenting cells (APCs) or sources of lymphocyte-active cytokines, may stimulate and affect lymphocyte functioning. Eosinophils share with CD4+ lymphocytes expression of a number of receptors, including CD4 and IL-2R, and specific alpha-4 integrins that may help in their common recruitment and activation. Further, elucidation of the interactions between lymphocytes and eosinophils will contribute to a broader understanding of the functioning of eosinophils in "normal" ongoing immune responses and in allergic disorders.

Expression of interleukin-5 and granulocyte-macrophage colony-stimulating factor in aspirin-sensitive and non-aspirin-sensitive asthmatic airways

Increased numbers of eosinophils and mast cells in the bronchial mucosa are characteristic features in subjects with aspirin-sensitive asthma. Interleukin-5 (IL-5) and granulocyte-macrophage colony-stimulating factor (GM-CSF) are involved in the activation, maturation, and perpetuation of survival of eosinophils. Immunohistochemical techniques were therefore used to study the expression of IL-5 and GM-CSF on frozen bronchial biopsies from 13 aspirin-sensitive asthmatic (ASA) and 8 non-ASA (NASA) subjects. Aspirin sensitivity was diagnosed by lysine-aspirin inhalation provocation. ASA airways demonstrated a significant 2-fold increase in the total number of submucosal inflammatory cells expressing IL-5 (p = 0.03) and approximate 4- and 2-fold increases in the numbers of mast cells expressing IL-5 and GM-CSF (p = 0.02 and p = 0.04, respectively). There was also a 4-fold increase in the number of eosinophils expressing IL-5 (p = 0.004). These results suggest a central role for the mast cell and eosinophil in regulation of the inflammatory cell infiltrate of ASA airways by secretion of the hemopoietic cytokines IL-5 and GM-CSF.

Eosinophils in allergic reactions

Mainly located in the skin or mucosa of patients with allergic diseases, eosinophils contribute directly to tissue damage and chronic inflammation. The past year has seen significant advances in the study of the factors involved in the specific tissue recruitment of eosinophils, including chemoattractants and their receptors. New data have been obtained on the synthesis by eosinophils of various cytokines mostly released by immune complexes.

Interleukin-5 mRNA expressed by eosinophils and gamma/delta T cells in parasite-immune sheep

Interleukin (IL)-5 is produced by variety of cell types and contributes to both lymphocyte development an eosinophil terminal differentiation in vitro. The coincidence of worm expulsion and eosinophilia in sheep infected with the gastrointestinal nematode Trichostrongylus colubriformis suggest that eosinophils may be involved as effector cells in host immunity against parasite infection. The role of IL-5 in this process was investigated by observing the distribution of IL-5 mRNA+ cells in the small intestine, mesenteric lymph nodes (MLN) and Peyer's patches (PP) by an in situ hybridization technique using a murine IL-5 riboprobe. IL-5 mRNA+ cells were distributed throughout the lamina propria (LP) of the small intestine from the tips of the villi to the muscularis mucosae and in the parafollicular areas of MLN and PP in both naive and immune sheep. The phenotypes of IL-5 mRNA+ cells was explored by simultaneous eosin and immunohistochemical staining using a monoclonal antibody recognizing the T19 marker, which identifies a major subset of gamma/delta TCR+ cells in sheep. In immune sheep, there was about a five-fold increase in the number of eosinophils and IL-5 cell mRNA+ cells in the LP, but there was no significant change in numbers of T19+ cells. Most of the IL-5 mRNA cells in the LP were eosinophils, but many of the T19+ cells also expressed IL-5 mRNA. In contrast, there were fewer eosinophils than T19+ cells in MLN of immune sheep and, compared to controls, a three-fold increase in T19+ cells and a five-fold increase in T19+/IL-5 mRNA+ double positive cells observed in immune sheep. In PP, there were very few eosinophils but substantial numbers of T19+ cells; however, no significant differences in numbers of eosinophils, T19+ or IL-5 mRNA+ cells were observed between control and immune sheep. These results indicate that in sheep, both eosinophils and gamma/delta T cells are capable of IL-5 expression and suggest that IL-5 is an important regulatory factor in autocrine and paracrine activation of effector cells involved in parasite immune expulsion.