Characterization of human middle ear mucus glycoprotein in chronic secretory otitis media (CSOM)

Extending the chinchilla middle ear epithelial model for mucin gene investigation

OBJECTIVES

To investigate the expression of recently identified human mucin genes in an in vivo model of the chinchilla middle ear epithelium (CMEE).

METHODS

CMEE was harvested, RNA was extracted and primers were designed for RT-PCR to assess for expression of mucin genes Muc6, Muc17 and Muc18. Further sequencing of these genes was also accomplished.

RESULTS

Mucin genes Muc6, Muc17 and Muc18 was assessed and found to be identical to the expression in human and mouse MEE.

CONCLUSION

This study further characterizes mucin gene expression in the CMEE and provides additional sequence data for chinchilla middle ear genes. The concordance of this gene expression data to that of both the human and mouse models further demonstrates the utility of this animal model in OM investigations.

Mucin gene 19 (MUC19) expression and response to inflammatory cytokines in middle ear epithelium

Mucin gene 19 (MUC19) has been identified as a major gel-forming mucin in the human middle ear (ME). The objectives of this investigation were to characterize the expression and assess the regulation of MUC19 in the ME cell culture models utilized in the study of otitis media (OM). Findings demonstrate that MUC19 is expressed in both human immortalized cell culture (HMEEC) and chinchilla primary epithelial culture (CMEEC). ME exposure to inflammatory cytokines TNF-alpha, IL-1beta, IL-6 and IL-8 up-regulate MUC19 transcription, most robustly after exposure to TNF-alpha. Kinetic experiments suggest a relative early response in MUC19 transcription and a down-regulation after prolonged exposure. Glycoprotein production was increased in response to the increased transcription as well. Similar to other mucin genes in the ME, MUC19 is differentially regulated after exposure to inflammatory cytokines. The large size, gel-forming properties and up-regulation in response to important inflammatory cytokines of MUC19 suggest that it has significant potential to play a role in both physiology and pathophysiology of the ME.

Interferon-gamma in suppurative otitis media: significance of otorrhoea type and disease outcome

BACKGROUND

Interferon-gamma has been reported to have an immunoregulatory role in otitis media with effusion. However, such a role remains to be determined in acute suppurative otitis media.

AIM

To determine the levels of interferon-gamma in middle-ear secretion in children with acute suppurative otitis media, and to determine the significance of interferon-gamma to the nature of otorrhoea and the outcome of otitis media.

SETTINGS AND DESIGN

Prospective, longitudinal follow up of patients selected from community and tertiary health centres.

METHODS

We selected children with acute suppurative otitis media, diagnosed as otorrhoea of less than three months' duration. Middle-ear secretions were collected by pipetting and stored at -80 degrees C. Interferon-gamma was assayed using enzyme-linked immunosorbent assay. The patients were treated and followed up for nine to 12 months, to separate those with resolved acute suppurative otitis media from those with chronic suppurative otitis media.

RESULT

The study initially included 358 cases of acute suppurative otitis media. Nine-month follow up was achieved in 304 patients (85 percent). Of these patients, acute suppurative otitis media resolved in 187 (61 percent), while chronic suppurative otitis media was evident in 117 (39 percent). The children with completed follow up comprised 173 boys and 131 girls, aged between four months and nine years (mean age 6.6 years; standard deviation 1.32). These children had purulent otorrhoea in 171 cases (56 percent) and mucoid otorrhoea in 133 cases (44 percent). The children's middle-ear secretion interferon-gamma concentrations ranged from 12 to 126 pg/ml. The mean middle-ear secretion interferon-gamma concentration was 27.2 pg/ml (standard deviation 8.8) in patients whose acute suppurative otitis media resolved, and 73.1 pg/ml (standard deviation 9.5) in those progressing to chronic suppurative otitis media. In children with purulent otitis media, the mean middle-ear secretion interferon-gamma concentration was 43.5 pg/ml (standard deviation 15.6); in those with mucoid otitis media, it was 74.3 pg/ml (standard deviation 19.1). Univariate analysis revealed significant differences in middle-ear secretion interferon-gamma concentration, comparing resolved acute suppurative otitis media and chronic suppurative otitis media cases (p = 0.00), and comparing purulent and mucoid otitis media cases (p = 0.00). Pearson correlation testing revealed significant inverse correlation between interferon-gamma concentration and middle-ear secretion immunoglobulin G concentration (p = 0.01), immunoglobulin E concentration (p = 0.03) and immunoglobulin A concentration (p = 0.00).

CONCLUSION

A high concentration of interferon-gamma in middle-ear secretions promotes chronicity of suppurative otitis media. Further research in this area may lead to the development of agents which assist the control of suppurative otitis media chronicity.

Gene expression differences in infected and noninfected middle ear complementary DNA libraries

OBJECTIVES

To investigate genetic differences in middle ear mucosa (MEM) with nontypeable Haemophilus influenzae (NTHi) infection. Genetic upregulation and downregulation occurs in MEM during otitis media (OM) pathogenesis. A comprehensive assessment of these genetic differences using the techniques of complementary DNA (cDNA) library creation has not been performed.

DESIGN

The cDNA libraries were constructed from NTHi-infected and noninfected chinchilla MEM. Random clones were picked, sequenced bidirectionally, and submitted to the National Center for Biotechnology Information (NCBI) Expressed Sequence Tags database, where they were assigned accession numbers. These numbers were used with the basic local alignment search tool (BLAST) to align clones against the nonredundant nucleotide database at NCBI.

RESULTS

Analysis with the Web-based statistical program FatiGO identified several biological processes with significant differences in numbers of represented genes. Processes involved in immune, stress, and wound responses were more prevalent in the NTHi-infected library. S100 calcium-binding protein A9 (S100A9); secretory leukoprotease inhibitor (SLPI); beta(2)-microglobulin (B2M); ferritin, heavy-chain polypeptide 1 (FTH1); and S100 calcium-binding protein A8 (S100A8) were expressed at significantly higher levels in the NTHi-infected library. Calcium-binding proteins S100A9 and S100A8 serve as markers for inflammation and have antibacterial effects. Secretory leukoprotease inhibitor is an antibacterial protein that inhibits stimuli-induced MUC1, MUC2, and MUC5AC production.

CONCLUSIONS

A number of genes demonstrate changes during the pathogenesis of OM, including SLPI, which has an impact on mucin gene expression; this expression is known to be an important regulator in OM. The techniques described herein provide a framework for future investigations to more thoroughly understand molecular changes in the middle ear, which will likely be important in developing new therapeutic and intervention strategies.

Cytokine regulation of mucin secretion in a human middle ear epithelial model

OBJECTIVES

Middle ear mucins are associated with otitis media (OM), contribute to hearing loss and are regulated by cytokines. This work investigates the regulation of mucin secretion from human middle ear epithelial cells (HMEEC) by inflammatory cytokines interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha) and cytokine inhibitors interleukin-1 receptor antagonist (IL-1ra) and anti-tumor necrosis factor-alpha antibody (TNFab).

METHODS

HMEEC were exposed to IL-1beta and TNF-alpha in a dose- and time-dependent manner. Cytokine stimulated HMEEC were also exposed to IL-1ra and TNFab in a dose-dependent manner. Mucin secretion was characterized by exclusion chromatography and liquid scintillation.

RESULTS

HMEEC exposed to IL-1beta and TNF-alpha demonstrated significant upregulation of mucin secretion in a dose-dependent fashion. Cultures exposed to IL-1beta at 100ng/ml and TNF-alpha at 200ng/ml showed increased mucin secretion in time-dependent experiments at 16h (P=0.00008) for TNF-alpha and 8 (P=0.028) and 16h (P=0.00001) for IL-1beta. IL-1ra and TNFab inhibited the effects of increased mucin secretion by IL-1beta and TNF-alpha.

CONCLUSIONS

IL-1beta and TNF-alpha upregulate mucin secretion from HMEEC in a dose- and time-dependant manner and these effects can be inhibited by cytokine blockade. Improved understanding of these mechanisms has the potential to alter the approach and management of OM and lead to novel therapeutic interventions.

Mucin gene cDNA sequence characterization in chinchilla middle ear epithelium

OBJECTIVES

To identify mucin genes in chinchilla middle ear epithelium and characterize complimentary deoxyribonucleic acid (cDNA) sequences to facilitate further investigations into mucin physiology and pathophysiology on a molecular level using the chinchilla model.

METHODS

Chinchilla mucin gene exploration and cDNA characterization was accomplished using reverse transcriptase-polymerase chain reactions (RT-PCR). Forward and reverse primer pairs were designed using consensus sequences available for human and rodent species. Chinchilla middle ear epithelium was harvested and primary cell cultures (CMEEC) were established. The CMEEC were explored for the expression of chinchilla mucin genes 1, 2, 4 and 5AC (cMuc1, cMuc2, cMuc4 and cMuc5AC). Identified cDNA amplicons for each of these genes was sequenced and homology compared to previously published human and rodent sequences.

RESULTS

CMEEC express all four of the mucin genes cMuc1, cMuc2, cMuc4 and cMuc5AC. cDNA amplicons for each of the genes were able to be sequenced with lengths ranging from 66 to 362 base pairs. Each of the chinchilla cDNA sequences expressed significant homology with published human and rodent cDNA for these mucin genes. A cDNA sequence for the housekeeping gene, beta-actin, was also identified.

CONCLUSIONS

Chinchilla middle ear epithelium grown in culture expresses the mucin genes 1, 2, 4 and 5AC, which have been identified as important in mucin regulation in the middle ear. cDNA sequences corresponding to these mucin genes were identified and may serve as important molecular tools in future studies of otitis media using the chinchilla model.

Evidence of T-helper cell 2 cytokine regulation of chronic otitis media with effusion

Cytokine and cellular patterns of effusions may reflect stages of middle ear inflammation. The local interplay between IL-2 and -4 is likely to play a crucial role in the switching of inflammation in the chronic stage. The T-helper cell 2 (Th2) cytokines IL-4, -5 and -13 and the Th2/Th1 cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) regulate the cellular and molecular processes of chronic inflammation in the middle ear and therefore the chronic condition of otitis media with effusion (OME). Early identification of the cytokine and cellular patterns of effusions can be helpful in directing the clinical treatment of OME.We hypothesized that IL-2 and the group of Th2 cytokines regulate chronic inflammation in the middle ear and chronic OME. Effusions from children with persistent OME were analysed to determine the presence of cytokines (the Th1 cytokine IL-2, the Th2 cytokines IL-4, -5 and -13 and the Th1/Th2 cytokine GM-CSF), inflammatory cells (CD4+ T cells, eosinophils, macrophages and neutrophils) and mucin. Cytokines were evaluated by means of a quantitative "sandwich"-type ELISA, inflammatory cells by means of alkaline phosphatase-anti-alkaline phosphatase immunocytostaining and mucin by means of a modified periodic acid-Schiff method based on a slot-blot technique. The cytokine pattern in effusions varied from patient to patient. GM-CSF correlated positively and IL-4 inversely with IL-2 and the increased level of IL-4 may have had an inhibitory effect on IL-2. IL-5 and -13 correlated with IL-4. Inflammatory cells correlated with cytokines as follows: CD4+ T cells with IL-2 and -4; macrophages and neutrophils with GM-CSF; and eosinophils with IL-5. Some cytokine-cellular correlations in effusions were reflected at the clinical level. The mucin content of effusions correlated with the concentrations of IL-4 (>10 pg/ml) and -13, suggesting involvement of IL-4 and -13 in upregulation of the middle ear mucin metabolism.

Middle ear epithelial mucin production in response to interleukin-6 exposure in vitro

OBJECTIVES

To investigate the role of the inflammatory cytokine interleukin-6 (IL-6) in the regulation of mucin secretion by middle ear epithelia.

MATERIALS AND METHODS

Primary chinchilla middle ear epithelial cultures were established and exposed to IL-6 in a dose- and time-dependent manner. Mucin secretion was characterized by exclusion chromatography and liquid scintillation.

RESULTS

Epithelial cultures exposed to increasing doses of IL-6 demonstrated greater amounts of mucin secretion (p=0.018). Additionally, cultures exposed to IL-6 at 50 ng/ml showed significant increased secretion of mucin over control in time-dependent experiments at 6-, 15- and 24-h time points (p=0.003).

CONCLUSIONS

IL-6 upregulates mucin secretion from cultured middle ear epithelial cells in a dose- and time-dependent manner. Elucidating the effect of specific cytokines on the regulation of mucin secretion is vital to understanding the pathophysiology of otitis media and the development of novel therapeutic strategies.

Middle ear epithelial mucin production in response to interleukin 1β exposure in vitro

OBJECTIVES: To investigate the role of the inflammatory cytokine interleukin-1β (IL-1β) in the regulation of mucin secretion by middle ear epithelia.

STUDY DESIGN AND SETTING: Primary chinchilla middle ear epithelial cultures were established and exposed to IL-1β in a dose- and time-dependent manner. Mucin secretion was characterized by exclusion chromatography and liquid scintillation.

RESULTS: Epithelial cultures exposed to increasing doses of IL-1β demonstrated greater amounts of mucin secretion ( P = 0.007). Additionally, cultures exposed to IL-1β at 50 ng/mL showed increased secretion of mucin over control noticeable at 6 hours, but significant at the 15- and 24-hour time points ( P > .0001 for each).

CONCLUSIONS: IL-1β upregulates mucin secretion from cultured middle ear epithelial cells in a dose-and time-dependent manner.

SIGNIFICANCE: Elucidating the effect of specific cytokines on the regulation of mucin secretion is vital to understanding the pathophysiology of otitis media and the development of novel therapeutic strategies.

Induction of mucous cell metaplasia by tumor necrosis factor alpha in rat middle ear: the pathological basis for mucin hyperproduction in mucoid otitis media

Mucoid otitis media (MOM), one of the leading causes of acquired hearing loss in children, is characterized by mucous cell hyperplasia in the middle ear cleft associated with mucin accumulation in the middle ear cavity. The factors that stimulate mucous cell metaplasia-hyperplasia and mucin hyperproduction are poorly understood. Recent studies demonstrated that tumor necrosis factor alpha (TNF-alpha), present in human middle ear effusion, stimulated mucin production in vitro and up-regulated mucin gene expression in vivo. These findings suggest that TNF-alpha is important in the development of mucous cell metaplasia-hyperplasia. This study demonstrated that inoculation of TNF-alpha into the middle ear cavity followed by eustachian tube obstruction stimulated mucous cell metaplasia-hyperplasia in the middle ear cleft, accompanied by abundant mucin or mucin-like glycoproteins in the middle ear effusion--a phenotype of MOM in humans. This finding suggests that TNF-alpha plays a key role in the pathogenesis of MOM through induction of mucous cell metaplasia-hyperplasia and mucin production.

Histopathologic differences due to bacterial species in acute otitis media

OBJECTIVE

To compare selected features of histopathology in acute otitis media caused by various bacteria and examine potential differences due to bacterial species, as well as possible correlation to experimental and human clinical findings.

METHODS

Rat models of acute otitis media caused by Streptococcus pneumoniae (MC), non-typeable or type b Haemophilus influenzae (NTHI/HIB) or Moraxella catarrhalis (MC) were studied longitudinally up to 6 months after bacterial challenge. Findings related to dynamics of goblet cell density, modeling and remodeling of bone tissue structures and polyp, as well as fibrous adhesion formation and persistence are presented.

RESULTS

Middle ear goblet cell density progressed to peak 2 weeks after bacterial inoculation, thereafter gradually normalizing. However, density and accordingly middle ear secretory capacity was still significantly increased after 6 months in all bacteria, except MC. The HI species induced the highest increase. Initial osteoresorption was followed by massive osteoneogenesis, progressing to a peak after 2-3 months, followed by some degree of normalization, concurrently classic remodeling. Primarily SP, but also the HI species induced more new bone formation than MC. Mucosal polyp and fibrous adhesion formation occurred regardless of bacterial species. Most polyps appeared in the early phases and the HI species induced formation of more polyps and adhesions than the other bacteria.

CONCLUSION

Acute middle ear infection with the Haemophilus species induce the highest increase of mucosal secretory capacity, lasting for at least 6 months after the acute incident. Thus, a subsequent development of secretory otitis media seems more likely following infection with these bacteria. Equivalently, mucosal scarring observed as polyp and fibrous adhesion formation was more severe following Haemophilus infection. S. pneumoniae induced the most marked changes of bone tissue structures, seen as initial osteoresorption and subsequent osteoneogenesis. Overall, infection with M. catarrhalis induced the mildest changes.

Pattern changes of mucin gene expression with pneumococcal otitis media

OBJECTIVE

mucins, known to be important components of the mucociliary transport system in the middle ear and Eustachian tube, are subject to changes under inflammatory conditions. Which mucin genes are up-regulated or activated during an inflammatory reaction of the middle ear and Eustachian tube, however, is poorly understood. The purpose of this study was to characterize mucin gene expression in middle ears and Eustachian tubes with pneumococcal ear infection.

METHODS

sixteen rats received intrabullar inoculation of Streptococcus pneumoniae type 6A at 2.5x10(6) colony forming units (CFU). Four animals were sacrificed on days 1, 3, 7, and 14, respectively. The profile of mucin gene expression in the middle ear and Eustachian tube was examined by reverse transcription polymerase chain reaction (RT-PCR) at the above time points. Sixteen rats that received intrabullar inoculation of phosphate-buffered saline (PBS) served as controls.

RESULTS

the Muc2 mucin gene was expressed in middle ear mucosa of the control rats. Following pneumococcal inoculation, Muc1-Muc5 mucin genes were expressed in the middle ear mucosa in a time-dependent manner. In the Eustachian tube, the Muc2, Muc4 and Muc5 mucin genes were expressed in both control and pneumococcal inoculation groups.

CONCLUSION

Muc1, Muc3, Muc4, and Muc5 mucin genes were activated in the middle ear mucosa by pneumococci, which may contribute to hyper-production of mucin in acute pneumococcal otitis media.

The aetiology of otitis media with effusion: a review

Otitis media with effusion (OME) is the most common cause of deafness in children in the developed world. In this article we aim to present an overview of current research developments on the aetiology of OME and the resulting implications for treatment. In the model we describe, the primary event is inflammation of the middle ear mucosa, usually due to the presence of bacteria. This leads to the release of inflammatory mediators, which cause secretion of a mucin-rich effusion by up-regulating mucin genes. Prolonged stimulation of the inflammatory response and poor mucociliary clearance lead to persistence of the middle ear fluid, giving rise to the clinical presentation of OME. We describe OME in the following sequence: the initial production of the effusion, the composition of the effusion produced, and factors impairing clearance of the effusion.

Mucin gene expression in the rat middle ear: an improved method for RNA harvest

Mucins are heavily glycosylated proteins characterized by high molecular weight and heterogeneous structure. Mucin genes are expressed in a tissue- or epithelium-specific manner. Although mucins are known to be important structural components of the mucociliary transport system that protects epithelium against invading microorganisms, very little is known about mucin gene expression unique to the middle ear. This study demonstrated that middle ear messenger RNA specifically hybridized with rat MUC2 and human MUC2 (SMUC-41) complementary DNA probes. MUC3 and MUC5AC mucin genes, dominantly expressed in rodent intestine and trachea, were not detected in the rat middle ears in this study. The middle ear MUC2 messenger RNA harvested by lavage was characterized by a single transcript--unlike its counterpart in intestine and airways, which is characterized by polydispersity--suggestive of a better method for RNA analysis. It was concluded that rat middle ears possess a MUC2 mucin gene or homologue of human MUC2 (SMUC-41).

Heterogeneity in the protein cores of mucins isolated from human middle ear effusions: evidence for expression of different mucin gene products

High molecular weight mucins were isolated and purified from human middle ear effusions of children with Otitis Media with Effusion (OME) classified into three groups, (1) thick and (2) thin from anatomically normal children and (3) effusions from cleft palate patients. Amino acid analyses of the purified mucins from the three pools were similar but not identical with characteristic contents of serine threonine and proline (32%, 28%, and 38% for pools (1) (2) and (3) respectively). Proteinase resistant glycopeptide fragments corresponding to the tandem repeat domains of cloned mucin genes showed marked differences both between the three mucin pools and with the composition of the tandem repeat sequences of the cloned mucin genes expressed in the airways. Studies on the antigenic identity of middle ear mucins found an epitope likely to be present on MUC5AC, but only accounting for a maximum of 15% by weight and no reactivity was found with antibodies to MUC2 or MUC1. A polyclonal antibody raised to thick effusion mucins reacted strongly with human salivary mucin suggesting the presence of MUC5B epitopes. These studies suggest that more than one mucin gene product is secreted by the human middle ear mucosa and that there may be further mucin genes expressed by the middle ear that have yet to be cloned.

Compositional differences between bilateral middle ear effusions in otitis media with effusion: evidence for a different etiology?

The aim of this study was to clarify the site of primary pathology in otitis media with effusion. Effusions were collected from 64 children with bilateral effusions at the time of myringotomy. The rheological properties and biochemical compositions of effusions were measured for 23 pairs of effusions, and the levels of the inflammatory mediators TNF alpha, IL-1beta, and IL-8 were measured in 41 pairs using specific enzyme-linked immunosorbent assays (ELISAs). Measurements from paired ears were compared using analysis of variance (ANOVA) tests and significant differences were found for reduced specific viscosity, mucin content, protein content, and levels of IL-8. The results demonstrate that the two ears have different immunological processes or rates of processes which might explain the significantly different rheological properties of effusions. This suggests that each ear undergoes pathological changes independently and has implications for using the opposite ear as a control in clinical trials.

Characterization of pig colonic mucins

Pig colonic mucins isolated from the adherent mucus gel in the presence of proteinase inhibitors were solubilized by homogenization and the component mucins fractionated by CsC1 density-gradient centrifugation. Polymeric and reduced pig colonic mucin were both largely excluded on Sepharose CL-2B, papain-digested colonic mucin was included. The M(r) values of polymeric, reduced and digested mucins were 5.5 x 10(6), 2.1 x 10(6) and 0.6 x 10(6) respectively. This suggests that pig colonic mucin is comprised of 2-3 subunits, each subunit containing 3-4 glycosylated regions. The intrinsic viscosities of polymeric, reduced and digested mucin were 240 ml.g-1, 100 ml.g-1 and 20 ml.g-1 respectively. Polymeric pig colonic mucin comprised 16% protein per mg of glycoprotein and was rich in serine, threonine and proline (43% of total amino acids). There were approx. 150 disulphide bridges and 53 free thiol groups per mucin polymer. A seventh of the protein content was lost on reduction. This protein was particularly rich in proline and the hydrophobic amino acids. Papain-digested pig colonic mucin contained 11% protein per mg of glycoprotein and was rich in serine, threonine, glutamate and aspartate. All types of amino acids with the exception of aspartate were lost on digestion. The amino acid analysis of the proteolytically digested regions of pig colonic mucin are markedly different to the tandem repeat regions of the human mucin genes shown to be expressed in the colon.

Isolation and partial characterization of rainbow trout (Oncorhynchus mykiss) gill mucin

Gill mucin from rainbow trout was isolated utilizing two rounds of cesium chloride density ultracentrifugation followed by gel filtration on Sepharose CL-2B. Neither density ultracentrifugation nor gel filtration alone was sufficient for purification of the mucin. Isolated gill mucin had a density of 1.5 g/ml and eluted at the void volume of the Sepharose CL-2B column. Silver-stained reducing 6% polyacrylamide gel electrophoresis of gill mucin produced a band at the origin with a smear entering the separating gel. There was no evidence of a link protein in gill mucin on reducing 12% polyacrylamide gel electrophoresis. Gill mucin had an amino acid profile similar to that of mucins in other species. Specifically, 35.1% of the total amino acids were represented by threonine and serine, while another 27.5% were alanine and proline. Gill mucin contained galactose (26.7 ± 3.2%), galactosamine (22.5 ± 4.4%), glucose (16.6 ± 8.7%), fucose (16.1 ± 1.5%), glucosamine (12.0 ± 1.9%) and mannose (5.1 ± 4.4%). Uronic acid levels from purified mucin were very low (0.7 ± 0.1%). Sialic acid was also present (0.06 g/g of mucin protein). The periodic acid-Schiff assay routinely utilized for detection of mucins was relatively insensitive for detection of gill mucin (6 × less sensitive than for pig gastric mucin) so a rabbit antiserum was raised. The antiserum produced profiles similar to the periodic acid-Schiff assay of fractions following gel filtration. Immunofluorescence of formalin-fixed rainbow trout gill tissue sections showed that the antiserum detected mucin within branchial goblet cells.

Preliminary characterization of mucin from effusions of cleft palate patients

Middle ear effusions from children undergoing myringotomy were classified into three groups-cleft palate, thick (mucoid), and thin (serous). Mucin was purified from each of the three groups using CsCI equilibrium density gradient centrifugation. Analysis of the cleft palate mucin on Sepharose CL-2B showed it was excluded and therefore of large molecular weight. It could be broken down into smaller glycopeptide units by proteolysis and these glycopeptides had, based on elution position, a larger hydrodynamic size than those from the thick mucin. Intrinsic viscosity measurements demonstrated that the intact mucins could be ranked in order of molecular space occupancy; cleft palate > thick > thin. Amino acid analysis showed the cleft palate mucin to have an amino acid composition similar to other mucins, with serine, threonine, and proline constituting 41% by weight of the protein core. Thiol analysis gave evidence of a possible difference in polymerization between the three mucins, in that thin (the smallest mucin) contained the lowest number of thiols. This preliminary analysis of cleft palate mucin suggests a mucin with larger glycopeptide units forming an intact mucin of larger hydrodynamic size than either thick or thin middle ear mucins from anatomically normal children.

Culture of human middle ear mucosal explants; mucin production

Middle ear mucosal biopsies could be maintained in culture for up to 7 days, the longest time attempted in this study. Mucin biosynthesis and secretion were measured by incorporation of 14C-glucosamine. Three peaks of radioactivity were present when the dialysed medium was chromatographed. Peak I which accounted for about 10% of the total radioactivity had properties characteristic of mucin. The other two peaks were not characteristic of mucins. Labelled macromolecules excluded on Sepharose 2B were also present in the tissue. Autoradiography of the explants showed that the labelled glucosamine was concentrated in the epithelial layer. Morphometry demonstrated that 1-2% of the epithelial cell volume consisted of goblet cells. The proportionate incorporation of radioactivity into macromolecules increased with increasing epithelial cell volume. This system will allow assessment of factors implicated in the pathogenesis of otitis media with effusion and the study of the action of pharmacological agents on biosynthesis and secretion.

Otitis media with effusion: components which contribute to the viscous properties

Middle ear effusions from children undergoing myringotomy were classified into thick (mucoid) and thin (serous) on the basis of their flow properties. Their composition was analysed and their rheological properties measured. The viscosity of the effusions was measured using a Contraves low shear viscometer and expressed as specific viscosity per mg/ml of non-dialysable solids present. In order to measure the effusion viscosity it was necessary to solubilize the effusion by mild homogenisation in a phosphate buffer pH 6.7 containing a cocktail of proteolytic inhibitors. The viscosity of mucoid effusions was significantly greater than that of the serous effusions. There was a small but measurable amount of proteolytic activity in the effusions, range 0.05-1.79 micrograms/mg of non-dialysable solids. This proteolytic activity was not significantly different between the thick and thin effusions and was therefore unlikely to explain the difference in viscosity. Analysis of the constituents of the effusions showed that glycoprotein and DNA but not protein nor lipid were significantly higher in the mucoid effusions compared to the serous effusions. The viscosity of the effusions correlated with the glycoprotein concentration but not with the protein or lipid concentration. Under certain circumstances the DNA concentration did correlate with the viscosity of the effusion. However, digestion with a proteinase free DNase did not reduce the viscosity of the effusion. These results demonstrate that classifying effusions as thick and thin based on visual inspection and flow properties is valid and that the only constituent present in the effusions that determines viscosity is mucin.

Comparative analysis of murine T lymphocyte responses to cartilage proteoglycans

Cartilage proteoglycans are large molecules consisting of several sub-regions each of which comprises homologous repeating subunits. Comparisons of murine primed popliteal lymph node responses to human cartilage proteoglycans in BALB and B10 congenic mice showed that the major histocompatibility complex (MHC) influences T cell responsiveness to this antigen. H-2k and H-2d were higher responders than H-2b. Responses were MHC class II-restricted, and human cartilage proteoglycans were cross-reactive with mouse cartilage proteoglycans for a BALB/c T cell line. The proportion of proteoglycan-specific T lymphocytes in BALB/c primed popliteal lymph nodes was about 45% lower in females than males. These results show that in mice both MHC haplotype and sex can determine T lymphocyte responsiveness to cartilage proteoglycans. If the same mechanisms apply in humans they could be important in determining the HLA-DR haplotype associations and the predilection of rheumatoid arthritis for females.