Phenotype of IL-16-producing cells in bronchial mucosa: evidence for the human eosinophil and mast cell as cellular sources of IL-16 in asthma

Mast Cells and Interleukins

Mast cells play a critical role in inflammatory diseases and tumor growth. The versatility of mast cells is reflected in their ability to secrete a wide range of biologically active cytokines, including interleukins, chemokines, lipid mediators, proteases, and biogenic amines. The aim of this review article is to analyze the complex involvement of mast cells in the secretion of interleukins and the role of interleukins in the regulation of biological activities of mast cells.

Mast cell tissue heterogeneity and specificity of immune cell recruitment

Mast cells occupy a unique niche within tissues as long lived perpetrators of IgE mediated hypersensitivity and anaphylaxis, as well as other immune responses. However, mast cells are not identical in different tissues and the impact of this tissue heterogeneity on the interaction with other immune cells and on defined immune responses is still unclear. In this review, we synthesize the characteristics of mast cell heterogeneity in the gut and the skin. Furthermore, we attempt to connect mast cell heterogeneity with functional diversity by exploring differences in mast cell-induced immune cell recruitment in these two model organs. The differential expression of certain receptors on mast cells of different tissues, notably tissue-specific expression patterns of integrins, complement receptors and MRGPRX2, could indicate that tissue environment-dependent factors skew mast cell-immune cell interactions, for example by regulating the expression of these receptors.

Deficiency of leukocyte-specific protein 1 (LSP1) alleviates asthmatic inflammation in a mouse model

Background

Asthma is a major cause of morbidity and mortality in humans. The mechanisms of asthma are still not fully understood. Leukocyte-specific protein-1 (LSP-1) regulates neutrophil migration during acute lung inflammation. However, its role in asthma remains unknown.

Methods

An OVA-induced mouse asthma model in LSP1-deficient (Lsp1^−/−) and wild-type (WT) 129/SvJ mice were used to test the hypothesis that the absence of LSP1 would inhibit airway hyperresponsiveness and lung inflammation.

Results

Light and electron microscopic immunocytochemistry and Western blotting showed that, compared with normal healthy lungs, the levels of LSP1 were increased in lungs of OVA-asthmatic mice. Compared to Lsp1^−/− OVA mice, WT OVA mice had higher levels of leukocytes in broncho-alveolar lavage fluid and in the lung tissues (P < 0.05). The levels of OVA-specific IgE but not IgA and IgG1 in the serum of WT OVA mice was higher than that of Lsp1^−/− OVA mice (P < 0.05). Deficiency of LSP1 significantly reduced the levels of IL-4, IL-5, IL-6, IL-13, and CXCL1 (P < 0.05) but not total proteins in broncho-alveolar lavage fluid in asthmatic mice. The airway hyper-responsiveness to methacholine in Lsp1^−/− OVA mice was improved compared to WT OVA mice (P < 0.05). Histology revealed more inflammation (inflammatory cells, and airway and blood vessel wall thickening) in the lungs of WT OVA mice than in those of Lsp1^−/− OVA mice. Finally, immunohistology showed localization of LSP1 protein in normal and asthmatic human lungs especially associated with the vascular endothelium and neutrophils.

Conclusion

These data show that LSP1 deficiency reduces airway hyper-responsiveness and lung inflammation, including leukocyte recruitment and cytokine expression, in a mouse model of asthma.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02078-7.

Interleukin-16 aggravates ovalbumin-induced allergic inflammation by enhancing Th2 and Th17 cytokine production in a mouse model

Asthma is a chronic inflammatory disease that involves a variety of cytokines and cells. Interleukin-16 (IL-16) is highly expressed during allergic airway inflammation and is involved in its development. However, its specific mechanism of action remains unclear. In the present study, we used an animal model of ovalbumin (OVA)-induced allergic asthma with mice harboring an IL-16 gene deletion to investigate the role of this cytokine in asthma, in addition to its underlying mechanism. Increased IL-16 expression was observed during OVA-induced asthma in C57BL/6J mice. However, when OVA was used to induce asthma in IL-16^-/- mice, a diminished inflammatory reaction, decreased bronchoalveolar lavage fluid (BALF) eosinophil numbers, and the suppression of OVA-specific IgE levels in the serum and BALF were observed. The results also demonstrated decreased levels of T helper type 2 (Th2) and Th17 cytokines upon OVA-induced asthma in IL-16^-/- mice. Hence, we confirmed that IL-16 enhances the lung allergic inflammatory response and suggest a mechanism possibly associated with the up-regulation of IgE and the promotion of Th2 and Th17 cytokine production. This work explored the mechanism underlying the regulation of IL-16 in asthma and provides a new target for the clinical treatment of asthma.

Mast cells as sources of cytokines, chemokines, and growth factors

Mast cells are hematopoietic cells that reside in virtually all vascularized tissues and that represent potential sources of a wide variety of biologically active secreted products, including diverse cytokines and growth factors. There is strong evidence for important non-redundant roles of mast cells in many types of innate or adaptive immune responses, including making important contributions to immediate and chronic IgE-associated allergic disorders and enhancing host resistance to certain venoms and parasites. However, mast cells have been proposed to influence many other biological processes, including responses to bacteria and virus, angiogenesis, wound healing, fibrosis, autoimmune and metabolic disorders, and cancer. The potential functions of mast cells in many of these settings is thought to reflect their ability to secrete, upon appropriate activation by a range of immune or non-immune stimuli, a broad spectrum of cytokines (including many chemokines) and growth factors, with potential autocrine, paracrine, local, and systemic effects. In this review, we summarize the evidence indicating which cytokines and growth factors can be produced by various populations of rodent and human mast cells in response to particular immune or non-immune stimuli, and comment on the proven or potential roles of such mast cell products in health and disease.

Identification and characterization of pro-interleukin-16 from mud crab Scylla paramamosain: The first evidence of proinflammatory cytokine in crab species

IL-16 is a pro-inflammatory cytokine originally designated as a lymphocyte chemoattractant factor. In mammal and avian, it has been characterized as an essential regulator of various cellular processes including cell recruitment and activation against pathogen invasion. So far, neither of the full-length of IL-16 homologue nor the response mechanism against pathogen was reported in crab species. In the present study, the pro-IL-16 homologue was firstly cloned and characterized from mud crab Scylla paramamosain. The full-length Sp-pro-IL-16 consisted of 4107 bp with an opening reading frame encoding 1369 amino acids. Multiple alignment analysis showed the putative amino acid sequence of Sp-pro-IL-16 had about 73.86% identity with Litopenaeus vannamei pro-IL-16. Additionally, two conserved PDZ domains and protein binding sites were found in Sp-pro-IL-16 and showed high similarities about 94.19% and 51.14% with their Litopenaeus vannamei and Mus musculus counterparts. RT-PCR analysis indicated that Sp-pro-IL-16 transcripts were constitutively expressed in all tissues examined with an extreme high level in hepatopancreas. Moreover, Sp-pro-IL-16 transcripts in hepatopancreas were significantly up-regulated 15-fold at 72 h after Vibrio alginolyticus challenge and 3.5-fold at 12 h after virus-analog Poly (I:C) challenge. The Western blot analysis revealed that Sp-pro-IL-16 can be cleaved to its bioactive form, an approximately 35 kDa mature IL-16, and the protein levels of both pro-IL-16 and mature IL-16 increased after Vibrio alginolyticus challenge. It is the first experimental identification of pro-inflammatory cytokine IL-16 in arthropods. This study could shed new light on further understanding of the response mechanism of pro-inflammatory cytokine IL-16 in Scylla paramamosain against pathogens. Meanwhile, it brought new insight into the origin and evolution of IL-16 in crab species.

IL-14 and IL-16 are expressed in the thyroid of patients with either Graves' disease or Hashimoto's thyroiditis

OBJECTIVES

Cytokines have an important role in orchestrating the pathophysiology in autoimmune thyroid disease. The aim of the current study was to analyse the expression of interleukin (IL)-14 and IL-16 in the thyroid tissue of patients with Graves' disease (GD), Hashimoto's thyroiditis (HT) or multinodular goitre (MNG) and in that of normal individuals, in patients' intrathyroidal CD4(+) and CD8(+) T cells, and in patient and normal cultured thyroid follicular cells.

METHODS

The expression of IL-14 and IL-16 mRNA and protein was investigated using reverse transcription-polymerase chain reaction (RT-PCR) amplification, and Western blotting and ELISAs, respectively.

RESULTS

IL-14 mRNA expression was detected in thyroid tissue from 8/9 GD, 3/4 HT and 3/13 MNG patients and 1/6 normal individuals, and IL-16 mRNA expression in thyroid tissue from 9/9 GD, 4/4 HT and 9/13 MNG patients and 4/6 normal individuals. IL-14 mRNA expression was detected in intrathyroidal CD4(+) and CD8(+) T cells from 2/2 GD and 2/2 HT patients, while IL-16 mRNA was detected in samples from 1/2 HT patients but not in those from either patient with GD. IL-14 and IL-16 mRNA expression was found in thyroid follicular cells derived from 2/2 patient with GD and 1/1 normal individual. IL-14 protein was detected in thyroid tissue from 6/6 GD, 1/1 HT and 0/6 MNG patients and 0/6 normal individuals, and IL-16 protein in thyroid tissue from 6/6 GD, 1/1 HT and 1/6 MNG patients and 0/6 normal individuals. Expression of IL-14 protein was stimulated in thyroid follicular cells derived from two patients with GD and one normal individual by peripheral blood mononuclear cell (PBMC)-conditioned medium. Treatment of thyrocytes from two patients with GD and one normal individual with PBMC-conditioned medium and tumour necrosis factor (TNF)-α stimulated IL-16 protein expression. In normal thyrocytes, IL-16 protein synthesis was induced also by IL-1β, IL-17A, IL-4 and transforming growth factor (TGF)-β.

CONCLUSIONS

The data provide evidence that the intrathyroidal production of IL-14 and IL-16 is associated with the pathogenesis of autoimmune thyroid disease. Thyroid follicular cells display the ability to express IL-14 and IL-16 mRNA and can be stimulated to express IL-16 protein, by a panel of cytokines, and IL-14 protein, by as yet unidentified factors.

Inflammation signals airway smooth muscle cell proliferation in asthma pathogenesis

Background

Airway inflammation stimulates proliferation of airway smooth muscle cell, which contributes to the development of hyperplasia and hypertrophy of smooth muscle cell. The increase in airway smooth muscle cell mass is believed to be due to an up-regulation of inflammatory mediators in the airway. It is now well recognized that chronic inflammation as well as airway hyper-responsiveness and remodeling of airway during inflammation, are crucial to asthma. Airway hyper-responsiveness is caused by increased cell proliferation or by hypertrophy of airway smooth muscle cell depending on the nature of the inflammatory stimulation. Airway smooth muscle cell proliferation in asthma is regulated by the proinflammatory cytokines including IL-1β and TNF-α. These proinflammatory cytokines have been shown to influence human airway smooth muscle cell proliferation in vitro, which is due to cyclooxygenase-2 expression, production of prostaglandin E2, and increased cAMP levels.

Conclusions

This review highlights the role of different proinflammatory cytokines in regulating airway smooth muscle cell growth and also focuses on regulation of differential gene expression in airway smooth muscle cell by growth factors and cytokines, also to bestow unique insight into the effects of conventional asthma therapies on airway smooth muscle cell proliferation and development of new therapeutic strategies to control asthma.

Association between serum IL-16 levels and the degree of sensitization in patients with atopic dermatitis

BACKGROUND

Interleukin (IL)-16 has been characterized as an immunomodulatory cytokine. Besides its chemotactic properties, IL-16 amplifies inflammatory processes and possesses immunoregulatory functions. Our aim was to investigate the association between serum IL-16 levels and the degree of allergic sensitization in patients with atopic dermatitis (AD).

METHODS

The serum level of IL-16 was measured by immunoenzymatic assays. Eosinophil cell count, serum total and specific IgE levels were assessed; prick tests were also carried out. Based on specific IgE levels and prick tests, AD patients were divided into sensitized and nonsensitized subgroups, and correlations among serum IL-16, total IgE levels and eosinophil cell counts were measured in the total patient group and in subgroups.

RESULTS

In the total patient group, significantly higher levels of IL-16 were found in the sera of patients with AD, compared to healthy individuals and patients with psoriasis. A significant correlation was detected between serum levels of IL-16 and total IgE, total IgE and eosinophil counts, but not between IL-16 and eosinophils. When sensitized and nonsensitized subgroups were compared, IL-16 levels showed a significant difference in subgroups that were divided based on specific IgE measurements, but not in those subgroups which were divided based on prick tests. On the other hand, serum total IgE levels showed a significant difference between sensitized and nonsensitized subgroups, assessed by the specific IgE method and also by prick test.

CONCLUSION

Serum IL-16 levels of AD patients correlate to some extent with sensitization. This correlation is not as strong as the correlation between total IgE levels and allergic sensitization.

Immunomodulation of caprine lentiviral infection by interleukin-16

Interleukin-16 (IL-16) is a proinflammatory cytokine produced by a variety of cells including lymphocytes, macrophages, mast cells, and eosinophils. We have shown in our previous studies increased expression of IL-16 mRNA and protein in caprine arthritis-encephalitis virus (CAEV)-infected goats blood. In this study, we determined the immunomodulatory effects of IL-16 in vitro using cells derived from CAEV infected and uninfected goats. Human recombinant IL-16 (rhIL-16) significantly increased chemotaxis of peripheral blood mononuclear cells (PBMCs) of both control and CAEV-infected goats. Pretreatment of PBMC with anti-goat CD4 monoclonal antibody inhibited IL-16-induced chemotaxis of PBMC of control and infected goats suggesting that IL-16 exerts its action in goats primarily by binding to CD4. The CAEV proviral DNA was less in caprine monocytes treated with rhIL-16 infected in vitro with CAEV. These data suggest inhibitory effect of IL-16 on viral integration. Flow cytometric studies indicated a trend toward IL-16-induced increased expression of lymphocyte activation markers. Combined with our previously reported data, these experiments suggest that increased IL-16 expression during CAEV infection may inhibit viral integration.

Biomarkers in asthma

PURPOSE OF REVIEW

The purpose of this review is to highlight seminal and current literature that informs our understanding of the clinical and investigative utility of biomarkers in asthma. Biomarkers derive from a variety of sources [bronchiolar lavage (BAL), sputum, exhaled breath, and blood], and have widely variant performance characteristics, and applicability.

RECENT FINDINGS

Increasing attention is given to biomarkers in exhaled breath, both gaseous (exhaled nitric oxide) and higher molecular weight moieties [in exhaled breath condensate (EBC)]. Current research in EBC analysis has focused on validation, standardization, and technical considerations, whereas research on exhaled nitric oxide (ENO) has moved to testing its predictive value in clinical situations. The use of advanced biostatistical techniques, and combinatorial analyses has led to additional advances in the utility of biomarkers.

SUMMARY

To date, the best validated, and best performing biomarkers for clinical asthma appear to be measures of inflammation in induced sputum, and measures of ENO. Some trials using ENO appear particularly promising for early clinical use. EBC metrics are at present too inchoate for clinical purposes. However, not all important clinical and research questions can be addressed with sputum, EBC, or ENO metrics, leaving an important place for BAL, bronchial biopsy, and perhaps EBC measurements in the research arena.

Preferential migration of T regulatory cells induced by IL-16

As a natural ligand for CD4, IL-16 has been shown to preferentially induce migration in Th1 cells, and, in long-term cultures with IL-2, IL-16 facilitates the expansion of CD4(+)CD25(+) cells. In addition, IL-16 has an immunomodulatory role in asthmatic inflammation, as exogenous administration significantly reduces inflammation and airway hyperreactivity. The mechanism for this, however, is not clear. Based on its functional characteristics and potential immunomodulatory role, we investigated the ability of IL-16 to recruit and influence the development of T regulatory (Treg) cells. We now demonstrate that IL-16 preferentially induces migration in a CD25(+)CTLA-4(+) human T cell subset and that responding cells produce IFNgamma and TGFbeta but not IL-10. These cells are relatively unresponsive to antigenic stimulation and can suppress proliferation and IL-5, but not IFNgamma, production by autologous T cells. We further demonstrate that IL-16-recruited cells are enriched for Forkhead box P3 (Foxp3). In addition, we find that IL-16 stimulation may facilitate de novo induction of Foxp3(+) Treg cells, because the stimulation of FoxP3-negative T cells for 48 h results in the expression of FoxP3 mRNA and protein. These data indicate that at sites of inflammation IL-16 may contribute to selective Treg cell expansion through the preferential induction of a migratory response from existing Treg cells, as well as by the induction of de novo generation of FoxP3(+) cells. These findings offer a potential mechanism for the immunosuppressive effects of IL-16 seen in Th2-mediated inflammation.

Effect of pollen-mediated oxidative stress on immediate hypersensitivity reactions and late-phase inflammation in allergic conjunctivitis

BACKGROUND

Allergic eye diseases are complex inflammatory conditions of the conjunctiva that are becoming increasingly prevalent and present an increasing economic burden because of direct and indirect health expenditures.

OBJECTIVE

We sought to identify factors that may synergize with antigen-induced allergic inflammation and lead to allergic conjunctivitis. We used a murine model of allergic conjunctivitis to test the effect of oxidative stress generated by pollen oxidases using nicotinamide adenine dinucleotide (reduced) or nicotinamide adenine dinucleotide phosphate (reduced) (NAD[P]H) as an electron donor present in pollen grains.

METHODS

Reactive oxygen species (ROS) generation by hydrated Ambrosia artemisiifolia pollen (short ragweed pollen; RWP) grains was determined by using 2'-7'-dihydro-dichlorofluorescein diacetate, nitroblue tetrazolium reduction, and Amplex Red assay. The RWP-induced changes in intracellular ROS levels were examined in A549 cells, human primary bronchial epithelial cells, and murine conjunctiva.

RESULTS

Ragweed pollen grains contain NAD(P)H oxidase activity, which is diphenyleneiodonium-sensitive and quinacrine-sensitive and sodium azide-resistant. These NAD(P)H oxidases generate a superoxide anion that can be converted to H2O2 by pollen grain-associated superoxide dismutase. These diffusible oxygen radicals from pollen grains increase intracellular ROS levels in cultured epithelial cells and murine conjunctiva. Similar phenomena were observed in sensitized and naive mice, indicating that the RWP-induced oxidative stress in conjunctival epithelium is independent of adaptive immunity. Inactivation of NAD(P)H oxidase activity in RWP decreases the immediate-type hypersensitivity and inflammatory cell infiltration into the conjunctiva.

CONCLUSION

Our data suggest that ROS generated by NAD(P)H oxidases in pollen grains intensify immediate allergic reactions and recruitment of inflammatory cells in murine conjunctiva.

Interleukin-12 and interleukin-16 in periodontal disease

The immune system plays an important role in the pathological process of periodontitis. Interleukin-12 (IL-12) is produced by monocytes, macrophages and neutrophils. These cells are proinflammatory infiltrates in periodontitis tissues. High IL-12 will contribute to the immune reaction to Th1 type. IL-12 is an inducer of INF-r production. IFN-gamma itself can also activate IL-12 production. Lipopolysaccharides (LPS) of periodontopathogens are also activators of IL-12. Interleukin-16 (IL-16) can cause the high affinity of IL-2 receptors on CD4+ cells and is chemotaxis to Th1 cells and CD4+ T cells. IL-16 can stimulate monocytes to produce proinflammatory cytokines and is highly associated with inflammation including arthritis, enteritis and allergic rhinitis. However, the information on IL-12 and IL-16 in periodontitis is not clear. In this study, 105 GCF samples were collected from 19 periodontal disease patients and 6 healthy ones. The clinical periodontal indices, the habits of cigarette smoking and alcohol drinking were recorded. ELISA was used to determine the levels of IL-12 and IL16 in the GCF. In the non-smoking/non-alcohol-drinking individuals: (1) the total amount of IL-12 (but not IL-16) was significantly higher in chronic periodontitis (CP) sites than gingivitis (G) or healthy (H) sites; (2) the diseased sites (CP + G) had a significantly higher total amount of IL-12 (but not IL-16) than the H sites. Among CP sites, both the concentration and total amount of IL-16 (but not IL-12) were significantly higher in alcohol drinkers/cigarette smokers as compared to the non-drinkers/non-smokers. CP sites of the drinkers/smokers also had significantly deeper probing pocket depth than sites of those without these two habits. IL-12 and IL-16 may be related to the pathogenesis of periodontal disease, but within the periodontitis sites, IL-16 may be related to disease severity in alcohol drinkers/smokers.

An update on bronchopulmonary dysplasia: is there a relationship to the development of childhood asthma?

There appears to be some interesting commonalities between asthma and BPD. The prevalence of both conditions is on the rise, both conditions tend to cluster in families, and they share wheezing phenotypes, i.e., mild-moderate reversible airway obstruction and a similar degree of response to pharmacological provocation. Furthermore, significant overlap exists with regard to the presence of elevated concentrations of airway inflammatory mediators concurrent with reduced levels of anti-inflammatory activity, in serum and BAL fluid, as well as histological evidence for airway 'remodelling'. Both BPD and asthma are characterized by increased smooth muscle contraction, and in asthma, the smooth muscle may be involved in the primary development of the asthmatic phenotype. Since wheezing is a common finding among children with BPD, an interesting question is whether BPD is a phenotypic variant of asthma?

Immune modulation of the pulmonary hypertensive response to bacterial lipopolysaccharide (endotoxin) in broilers

The lungs of broilers are constantly challenged with lipopolysaccharide (LPS, endotoxin) that can activate leukocytes and trigger thromboxane A2 (TxA2)- and serotonin (5HT)-mediated pulmonary vasoconstriction leading to pulmonary hypertension. Among broilers from a single genetic line, some individuals respond to LPS with large increases in pulmonary arterial pressure, whereas others fail to exhibit any response to the same supramaximal dose of LPS. This extreme variability in the pulmonary hypertensive response to LPS appears to reflect variability in the types or proportions of chemical mediators released by leukocytes. Our research has confirmed that TxA2 and 5HT are potent pulmonary vasoconstrictors in broilers and that broilers hatched and reared together consistently exhibit pulmonary hypertension after i.v. injections of TxA2 or 5HT. Previous in vitro studies conducted using macrophages from different lines of chickens demonstrated innate variability in the LPS-stimulated induction of nitric oxide synthase (iNOS) followed by the onset of an LPS-refractory state. The NOS enzyme converts arginine to citrulline and nitric oxide (NO). It is known that NO produced by endothelial NOS serves as a key modulator of flow-dependent pulmonary vasodilation, and it is likely that NO generated by iNOS also contributes to the pulmonary vasodilator response. Accordingly, it is our hypothesis that the pulmonary hypertensive response to LPS in broilers is minimal when more vasodilators (NO, prostacyclin) than vasoconstrictors (TxA2, 5HT) are generated during an LPS challenge. Indeed, inhibiting NO production through pharmacological blockade of NOS with the inhibitor Nomega-nitro-L-arginine methyl ester modestly increased the baseline pulmonary arterial pressure and dramatically increased the pulmonary hypertensive response to LPS in all broilers evaluated. Innate differences in the effect of LPS on the pulmonary vasculature may contribute to differences in susceptibility of broilers to pulmonary hypertension syndrome (ascites).

Neuropeptide-induced inhibition of IL-16 release from eosinophils

OBJECTIVES

Eosinophils are prominent inflammatory cells that respond to peripheral neuropeptides in vitro and in vivo. At inflammatory sites, cytokines activate distinct cellular and biochemical pathways that act in a coordinated fashion. We investigated whether peripheral neuropeptides can act as immunomodulators by influencing cytokine release from eosinophils.

METHODS

Human eosinophils were enriched using magnetic cell sorting, and IL-16 levels in supernatants from maintained eosinophils were measured by ELISA. Biological activity of IL-16 was confirmed in lymphocyte chemotaxis assays.

RESULTS

Substance P, vasoactive intestinal polypeptide, calcitonin gene-related peptide and secretoneurin reduced the IL-16 release from eosinophils; this effect was additive to that observed with GM-CSF or IL-5. Decreased IL-16 levels in supernatants resulted in reduced lymphocyte chemotaxis, whereas supernatants derived from SP-treated eosinophils stimulated lymphocyte chemotaxis, even though IL-16 was decreased.

CONCLUSIONS

Results suggest that distinct neuropeptides are able to reduce the number of lymphocytes at inflammatory sites during existing eosinophilia by inhibiting eosinophil IL-16 release, thus attenuating the pro-inflammatory action of lymphocytes and monocytes.

Histamine h(4) and h(2) receptors control histamine-induced interleukin-16 release from human CD8(+) T cells

Histamine is known to trigger the release of interleukin (IL)-16 from human CD8(+) cells. However, the individual roles of the presently known histamine receptor subtypes (H(1)-H(4)) in this inflammatory response have not been fully characterized. Histamine stimulation of human CD8(+) T lymphocytes purified from peripheral blood led to a 5- to 8-fold increase in the basal release of IL-16 within 24 h, and this increase was significantly blocked by the H(2)-selective antagonist, cimetidine, or by thioperamide, an antagonist of H(3) and H(4) receptors, respectively. The H(1) antagonist pyrilamine showed limited effects. Agonists selective for H(2) (dimaprit), H(3/4) (R-(-)-alpha-methylhistamine), and H(4) (clobenpropit) were capable of inducing the release of bioactive IL-16 because CD8(+) cell supernatants induced CD4(+) cell migration, which was abrogated by an anti-IL-16 antibody. Furthermore, preincubation of lymphocytes with pertussis toxin abolished IL-16 release triggered by activation of the G(i/o)-coupled H(4) receptor but not by the H(2) receptor. Messenger RNA expression studies confirmed H(4), H(2), and H(1) expression in human CD8(+) lymphocytes, whereas H(3) mRNA was completely absent. All leukocyte populations investigated expressed mRNA for H(4), with highest levels found in eosinophils, dendritic cells, and tonsil B cells. H(4) expression was also detected in human lung, trachea, and various cells of human lung origin, such as fibroblasts, bronchial smooth muscle cells, epithelial, and endothelial cells. Since many of those are known sources of IL-16, immune cell- and lung cell-expressed H(4) receptors may have a general role in the control of this mediator of inflammatory disorders such as asthma.

Role of cytokines and chemokines in bronchial hyperresponsiveness and airway inflammation

Over the last decade there has been an intense interest in the potential role of cytokines and chemokines as important mediators in various atopic diseases, including asthma and the mechanisms by which these mediators regulate airway inflammation and bronchial hyperresponsiveness. This research effort has recently culminated in the publication of clinical studies that have assessed the role of interleukin (IL)-4 [Borish et al., Am J Respir Crit Care Med 160, 1816-1823 (1999)], IL-5 [Leckie et al., Lancet 356, 2144-2148 (2000)], and IL-12 [Bryan et al., Lancet 356, 2149-2153 (2000)] in allergic asthma, and the results have been disappointing. This is not surprising given the pleiotropic role cytokines play in the allergic response confirmed by numerous animal studies providing evidence of functional redundancy. The alternative view is that our current concepts in asthma pathogenesis need significant revision. This review will summarise the evidence for the role of cytokines and chemokines in various aspects of asthma pathophysiology; namely, bronchial hyperresponsiveness, eosinophil recruitment to the airways, mucus secretion, and airway remodelling.

Activation of CD8 T cells induces expression of CD4, which functions as a chemotactic receptor

It was previously shown that costimulation of CD8(+) lymphocytes results in de novo expression of CD4. This study expanded on this observation to investigate the function of CD4 on CD8 cells. The ability of costimulated CD8 cells to respond to interleukin 16 (IL-16), a ligand that binds CD4 and induces cellular chemotaxis, was examined. IL-16-mediated ligation of CD4 expressed on CD8 T cells was found to induce an intracellular signal that directs migration of these cells in vitro. Thus, expression of CD4 on a CD8 lymphocyte has functional importance and may serve to control distribution of newly activated CD8 T cells in vivo.

Increased expression of the chemoattractant cytokines eotaxin, monocyte chemotactic protein-4, and interleukin-16 in induced sputum in asthmatic patients

BACKGROUND

Induced sputum from asthmatic patients has been recently used to assess inflammatory cells. We have previously reported an increased expression of Th-2-type cytokines in induced sputum of asthmatic patients. C-C chemokines, particularly eotaxin and monocyte chemotactic protein (MCP)-4, are associated with eosinophilic infiltration. Interleukin (IL)-16 is associated with chemotactic activity for CD4+ cells. Chemokine expression in BAL and bronchial biopsy specimens has been demonstrated in asthmatic airways, but not in induced sputum.

METHODS

We examined whether eotaxin, MCP-4, and IL-16 expression could be detected in induced sputum of asthmatic patients (n = 10), and whether the expression was increased compared to normal control subjects (n = 9). Eotaxin, MCP-4, and IL-16 immunoreactivity were determined by immunocytochemistry. In addition, inflammatory cells were investigated using markers for T cells (CD3), eosinophils (major basic protein [MBP]), macrophages (CD68), neutrophils (elastase), and epithelial cells (cytokeratin).

RESULTS

Our results showed that there was a significant difference in the percentages of MBP-positive and epithelial cells between asthmatic patients and normal control subjects (p < 0.05). However, there was no difference between these two groups in the percentage of CD3-, elastase-, and CD68-positive cells. Immunoreactivity for eotaxin, MCP-4, and IL-16 was expressed in the induced sputum of all asthmatic patients, and expression of these chemotactic cytokines was significantly greater than in control subjects (p < 0.001, p < 0.005, and p < 0.001, respectively).

CONCLUSIONS

This study showed that induced sputum could be used to detect chemokines in patients with bronchial asthma, and that the upregulation of chemotactic cytokines in the airways can be seen using noninvasive techniques.

Interleukin-16 Supports the Migration of Langerhans Cells, Partly in a CD4-Independent Way

Migration of cutaneous dendritic cells is essential for the induction of primary immune responses. Chemotaxis plays an important part in guiding migrating cells through the skin. Therefore, we investigated the influence of interleukin-16, a potent chemoattractant, on the migratory properties of cutaneous dendritic cells. Interleukin-16 added to murine and human skin explant cultures, enhanced emigration of Langerhans cells as well as dermal dendritic cells out of the skin. In contrast to tumor necrosis factor-alpha, intradermally injected interleukin-16 did not reduce the density of Langerhans cells suggesting a chemotactic rather than a mechanistic migration-inducing effect of interleukin-16. In support of these findings, the known migration-promoting effect of tumor necrosis factor-alpha in skin explant cultures could be neutralized by anti-interleukin-16 antibody and vice versa, indicating different but cooperative ways of action for both cytokines. In whole skin explant cultures blocking of the interleukin-16 effect was also achieved with a monoclonal antibody against CD4, the receptor for interleukin-16. In contrast, in cultures of murine epidermis alone no blocking by anti-CD4 became obvious and in CD4-deficient mice Langerhans cell migration in response to interleukin-16 was maintained. This suggests that another receptor for interleukin-16 might be operative for Langerhans cells in the mouse epidermis. Finally, we detected interleukin-16-positive cells in the dermis of skin explants, tumor necrosis factor-alpha-treated and contact allergen-treated skin. Taken together, it seems likely that locally secreted interleukin-16 might serve to enhance the migration of cutaneous dendritic cells and optimize the response to foreign antigen encountering the skin.

Human focal cerebral infarctions induce differential lesional interleukin-16 (IL-16) expression confined to infiltrating granulocytes, CD8+ T-lymphocytes and activated microglia/macrophages

Focal cerebral ischemia elicits a strong inflammatory response which readily participates in lipid oxygenation, edema formation, apoptotic cell death and tissue remodeling. Within these conditions, cytokines are key players of cell activation and are crucial for delayed mechanisms of ischemic damage. Mature IL-16 is an immunomodulatory cytokine, exerting CD4 dependent and independent effects and is characterized by chemotactic activity, induction of early gene phosphorylation, stimulation of pro-inflammatory IL-1beta, IL-6, TNFalpha expression in monocytic cells and also modulates apoptosis. We have now analyzed expression of IL-16 in 20 brains of patients following focal cerebral infarctions (FCI, n=20). Compared to normal control brains (n=3), IL-16 was expressed by infiltrating immune cells such as neutrophils, CD8+ lymphocytes and activated CD68+ microglia/macrophages accumulating in lesion associated reactive zones and in peri-vascular regions. IL-16+ cells accumulated significantly (P<0.0001) in the necrotic lesion and at bordering peri-lesional areas at day 1-2 reaching maximum levels at day 3-4 (P<0.0001). Also, peri-vascular IL-16+ cells reached maximum levels at day 3-4 (P<0.0001) following infarction and decreased after several weeks. During the early microglial activation period, IL-16+ microglia/macrophages coexpress the activation antigen MRP-8. The accumulation of IL-16+ granulocytes, IL-16+, CD8+ lymphocytes and activated IL-16+, CD68+, CD4- microglia/macrophages, early after infarction suggest a CD4 independent, paracrine role of IL-16 in the postinjury inflammatory response, such as recruitment and activation of immune cells leading to microvessel clustering and blood-brain barrier disturbance resulting in secondary damage.

Regulation of allergic airways inflammation by cytokines and glucocorticoids

Cytokines mediate the allergic inflammatory response of the airways, and glucocorticosteroids ameliorate allergy symptoms by regulating cytokine expression. Recent studies provide insight into the manner by which cytokines work together to mediate allergic airway disease. Real progress has also been gained in our understanding of subcellular mechanisms of allergic inflammation, particularly the role of transcription factors in regulating the expression of specific cytokine profiles and the differentiation of the TH2 subset. This article provides an update of recently reported findings in this field and highlights emerging concepts of allergic inflammation.

Interleukin (IL)-4/IL-9 and exogenous IL-16 induce IL-16 production by BEAS-2B cells, a bronchial epithelial cell line

Previous studies have suggested that bronchial epithelial cells may perpetuate airway inflammation. We have reported that the bronchial epithelial cell line BEAS-2B can produce interleukin (IL)-16, a potent chemoattractant for CD4+ T cells. IL-16 is thought to regulate airway inflammation in asthmatics. Recent studies showed that IL-4 induces inflammatory cytokines in bronchial epithelial cells and that IL-9 is a candidate gene for development of asthma. The present study demonstrated that BEAS-2B cells produced specifically IL-16 by synergistic effects of IL-4 + IL-16, or IL-9 + IL-16, and that the synthesized IL-16 induced migration of CD4+ T cells. This study is a first report indicating that IL-16 production may be maintained by an autocrine machinery by epithelial cell-derived IL-16 with IL-4 and IL-9 in asthma.

Increased expression of IL-16 immunoreactivity in bronchial mucosa after segmental allergen challenge in patients with asthma

BACKGROUND

We have previously shown increased expression of the CD4(+) cell chemoattractant IL-16 in bronchial mucosa of patients with asthma. We investigated the effects of allergen challenge on airway IL-16 expression.

METHODS

We investigated the expression of IL-16 immunoreactivity in bronchial biopsy samples obtained from atopic asthmatic subjects (n = 19) and normal subjects (n = 6) 24 hours after segmental allergen challenge. Control biopsy samples were obtained either at baseline or after diluent challenge. IL-16 expression was correlated to numbers of CD4(+) cells, CD25(+) cells, and activated eosinophils. IL-16 bioactivity was assessed in bronchoalveolar fluid obtained from patients with asthma.

RESULTS

IL-16 expression was higher in control biopsy specimens obtained from subjects with asthma compared with normal subjects (P<.05). In patients with asthma, numbers of IL-16 immunoreactive cells were significantly higher in biopsy specimens obtained after allergen challenge compared with control biopsy specimens (P<.001). Allergen provocation was associated with release of IL-16 in bronchoalveolar fluid in patients with asthma. In normal subjects, there was no difference in the number of IL-16-immunoreactive cells in biopsy specimens obtained after allergen challenge compared with biopsy specimens obtained after diluent challenge. Allergen challenge was associated with an increase in the numbers of EG2(+) eosinophils in patients with asthma but not in normal subjects. IL-16 expression correlated with the numbers of CD4(+) cells and CD25(+) cells after allergen challenge in asthmatic subjects with a provocative concentration required to decrease the FEV(1) by 20% of its baseline value (PC(20)FEV(1)) < 4 mg/mL. IL-16-immunoreactive cells were identified mainly as T cells and eosinophils in asthmatic subjects after allergen challenge.

CONCLUSION

Endobronchial allergen provocation in atopic asthmatic patients resulted in increased airway expression of IL-16 and release of bioactive IL-16 in airways. IL-16 may contribute to the immunoregulation of the inflammatory infiltrate in the airways in response to antigen.

The pathology of asthma: brief review

The presence of chronic airway inflammation in asthmatic patients has been known for over a century, but the relationship of this inflammatory process to the pathogenesis of reversible airflow obstruction and non-specific bronchial hyperresponsiveness remains unclear. In recent years, the increasing ability to sample the lower respiratory tract of living asthmatic patients, coupled with revolutionary advances in immunology and molecular biology, has resulted in extensive evaluation of inflammatory cells and mediators implicated in the pathogenesis of asthma. In addition, there is increasing recognition that airway remodeling, characterized by thickening of all compartments of the airway wall, may have profound consequences on the mechanics of airway narrowing in asthma and contribute to the chronicity and progression of the disease. In this brief review, I will describe the gross and microscopic pathology of asthma, the process of airway remodeling and its functional consequences, and speculate on future directions to improve our understanding of the structural changes of asthma and their pathogenic role.

Molecular pathology of allergic disease: I: lower airway disease

Asthma is a complex disorder associated with eosinophil infiltration and the activation of T lymphocytes within the airways. Recent advances in the pathophysiologic mechanisms of asthma point to the importance of eosinophil-basophil progenitor cells and a family of transcription factors that underlie the development of T(H)2-type responses. Further research is needed to address the development of chronic inflammatory changes, the role of profibrotic cytokines, and especially their reliance on eosinophils in the lungs.