Localization of the GM1 ganglioside in the vestibular system using cholera toxin

Clinical Features and Neurotologic Findings in Patients With Acute Unilateral Peripheral Vestibulopathy Associated With Antiganglioside Antibody

BACKGROUND AND OBJECTIVES

Anecdotal studies have reported the presence of antiganglioside antibodies in acute unilateral peripheral vestibulopathy (AUPV). This study aimed to determine the prevalence, clinical characteristics, and neurotologic findings of AUPV associated with antiganglioside antibodies.

METHODS

Serum antigangliosides were measured in consecutive patients with AUPV according to the Bárány Society criteria during the acute and recovery phases in a referral-based university hospital in South Korea from September 2019 to January 2023. Clinical characteristics and neurotologic findings were compared between those with and without antiganglioside antibodies. The results of video-oculography, video head impulse and bithermal caloric tests, and other neurotologic evaluations including ocular and cervical vestibular-evoked myogenic potentials and subjective visual vertical were compared between the 2. MRIs dedicated to the inner ear were also conducted when considered necessary.

RESULTS

One hundred five patients (mean age ± SD = 60 ± 13 years, 57 male) were included for analyses. During the acute phase, 12 patients (12/105, 11%) were tested positive for serum antiganglioside antibodies, including anti-GQ1b immunoglobulin (Ig) G (n = 5) or IgM (n = 4), anti-GM1 IgM (n = 3), and anti-GD1a IgG (n = 1, including 1 patient with a positive anti-GQ1b antibody). Patients with antiganglioside antibodies showed lesser intensity of spontaneous nystagmus (median [interquartile range] = 1.8 [1.2-2.1] vs 3.4 [1.5-9.5], p = 0.003) and a lesser degree of canal paresis (30 [17-47] vs 58 [34-79], p = 0.028) and gain asymmetry of the vestibulo-ocular reflex for the horizontal semicircular canal during head impulse tests (0.07 [-0.04 to 0.61] vs 0.36 [0.18-0.47], p = 0.032) than those without antibodies. Negative conversion of antibodies and vestibular recovery were observed in most patients (6/8, 75%). Among 30 patients with AUPV with 4-hour delayed 3D fluid-attenuated inversion recovery dedicated to the inner ear, gadolinium enhancement was observed in 18 (18/30, 60%), either in the vestibule (n = 9), semicircular canal (n = 6), or vestibular nerve (n = 5). The positivity rates based on specific antibodies could not be determined due to limited sample sizes.

DISCUSSION

The association between antiganglioside antibodies and AUPV suggests an immune-mediated mechanism in acute vestibular failure and extends the clinical spectrum of antiganglioside antibody syndrome.

Dendritic cell-targeting DNA-based mucosal adjuvants for the development of mucosal vaccines

In order to establish effective mucosal immunity against various mucosal pathogens, vaccines must be delivered via the mucosal route and contain effective adjuvant(s). Since mucosal adjuvants can simply mix with the antigen, it is relatively easy to adapt them for different types of vaccine development. Even in simple admixture vaccines, the adjuvant itself must be prepared without any complications. Thus, CpG oligodeoxynucleotides or plasmids encoding certain cDNA(s) would be potent mucosal adjuvant candidates when compared with other substances that can be used as mucosal adjuvants. The strategy of a DNA-based mucosal adjuvant facilitates the targeting of mucosal dendritic cells, and thus is an effective and safe approach. It would also provide great flexibility for the development of effective vaccines for various mucosal pathogens.

Ordered just so: lipid rafts and lymphocyte function

Immunologists have long been occupied with the description of cellular activation signaling events that originate with the stimulation of multichain immunoreceptors at the cell surface. These signals are transmitted by a protein-partner-signaling cascade through the cytoplasm to the nucleus, where they culminate in changes in gene expression, metabolic state, and entry into cell cycle. For T cells and B cells, these signaling cascades start with the ligation of the T cell receptor (TCR) and B cell receptor (BCR), respectively, and result in the recruitment and activation of related families of signaling molecules at the cell surface. Until recently, this gathering of signaling proteins was thought to occur within the featureless plasma membrane, a cellular organ that was envisioned as a boundary between the inner and outer components of the cell, but which contributed little to the signaling process. However, the past few years have seen the gradual realization that activation of signaling in lymphocytes takes place in and around specialized membrane subdomains called lipid rafts (also known as DIGs and GEMs). Here, we provide a brief overview of the analogous structures and compositions of lipid raft-associated signaling complexes in T cells and B cells, and the ways in which lymphocytes--and their pathogen adversaries--use lipid rafts to their benefit.

Cutting edge: the mucosal adjuvant cholera toxin redirects vaccine proteins into olfactory tissues

We tested the notion that the mucosal adjuvant cholera toxin (CT) could target, in addition to nasal-associated lymphoreticular tissues, the olfactory nerves/epithelium (ON/E) and olfactory bulbs (OBs) when given intranasally. Radiolabeled CT ((125)I-CT) or CT-B subunit ((125)I-CT-B), when given intranasally to mice, entered the ON/E and OB and persisted for 6 days; however, neither molecule was present in nasal-associated lymphoreticular tissues beyond 24 h. This uptake into olfactory regions was monosialoganglioside (GM1) dependent. Intranasal vaccination with (125)I-tetanus toxoid together with unlabeled CT as adjuvant resulted in uptake into the ON/E but not the OB, whereas (125)I-tetanus toxoid alone did not penetrate into the CNS. We conclude that GM1-binding molecules like CT target the ON/E and are retrograde transported to the OB and may promote uptake of vaccine proteins into olfactory neurons. This raises concerns about the role of GM1-binding molecules that target neuronal tissues in mucosal immunity.

Carbohydrate composition of stereociliary glycocalyx of the utricle of guinea pig inner ear

The carbohydrate composition of the stereociliary glycocalyx of the utricle was analysed quantitatively. The utricular sensory epithelium was collected from adult albino guinea pigs, and its apical surface structure was blotted onto a PVDF membrane, which was then subjected to acid hydrolysis. The hydrolysate was treated with 1-phenyl-3-methyl-5-pyrazolone for labelling and analysed by reversed-phase HPLC coupled with detection of UV absorbance at 245 nm. Man, GlcN, GaIN, Glc, Gal and Fuc were detected and estimated to be 211, 219, 46, 1,270, 266 and 36 pmoles per 10 utricular maculae, respectively. The presence of Man indicates the presence of N-linked glycoconjugates, and the considerable amounts of GLcN and Gal suggest the presence of complex-type N-glycosides, poly-lactosamine and/or keratan sulfate. The relatively low GaIN content indicates that O-glycosides, chondroitin sulfates and GaINAc-containing glycosphingolipids, i.e. gangliosides and globosides, are minor components. Electronmicroscopic and confocal laser scanning microscopic observations revealed that the blotted apical surface structure constituted mostly the ciliary bundle. Consequently, the observed carbohydrate composition is probably that of the stereociliary glycocalyx of the utricular sensory epithelium.

Carbohydrate distribution in the living utricular macula of the guinea pig detected by lectins

Carbohydrate distribution in the fresh utricular macula of the guinea pig was analysed using lectins such as Concanavalin A (ConA), Dolichos biflorus agglutinin (DBA), peanut agglutinin (PNA), soybean agglutinin (SBA), Ulex europeus agglutinin (UEA-1) and wheat germ agglutinin (WGA) by means of confocal laser scanning microscopy. The ciliary bundle was strongly reactive to ConA, PNA, SBA and WGA but not to DBA and UEA-I, showing that the ciliary bundle has abundant D-galactose (GaI), N-acetyl-D-glucosamine (GlcNAc), D-mannose (Man) and sialic acid(s) (Sia) but not detectable amounts of L-fucose (Fuc) and terminal N-acetyl-D-galactosamine (GalNAc). Similar patterns of lectin bindings with moderate-to-weak intensities were observed on the non-cilial apical surface, on the surface of the otoconia and in the gelatinous layer of the otoconial membrane. On the contrary, the globular substance, a precursor of the otoconia, was scarcely reactive to any lectin examined, implying that it lacks glycoconjugates on its surface. Previous histochemical studies reported that the otoconial membrane possesses a much higher affinity for lectins that does the sensory epithelium (including the cilia) in the vestibular organ. This discrepancy suggests that factors in the preparation process may affect the otoconial membrane or the surface coat of the cilia to change their lectin affinity. Meanwhile, sialidase treatment augmented the affinity of the ciliary bundle for DBA and PNA, indicating that sialylated GalNAc and Gal are present on the vestibular ciliary bundle.

Auditory brainstem responses of CBA/J mice with neonatal conductive hearing losses and treatment with GM1 ganglioside

Exogenous administration of GM1 ganglioside to CBA/J mice with a neonatal conductive hearing loss ameliorates the atrophy of spiral ganglion neurons, ventral cochlear nucleus neurons, and ventral cochlear nucleus volume. The present investigation demonstrates the extent of a conductive loss caused by atresia and tests the hypothesis that GM1 ganglioside treatment will ameliorate the conductive hearing loss. Auditory brainstem responses were recorded from four groups of seven mice each: two groups received daily subcutaneous injections of saline (one group had normal hearing; the other had a conductive hearing loss); the other two groups received daily subcutaneous injections of GM1 ganglioside (one group had normal hearing; the other had a conductive hearing loss). In mice with a conductive loss, decreases in hearing sensitivity were greatest at high frequencies. The decreases were determined by comparing mean ABR thresholds of the conductive loss mice with those of normal hearing mice. The conductive hearing loss induced in the mice in this study was similar to that seen in humans with congenital aural atresias. GM1 ganglioside treatment had no significant effect on ABR wave I thresholds or latencies in either group.

Glycolipidic component of the epithelial cell coat of the endolymphatic sac

The endolymphatic sac (ES) is thought to synthesize and secrete glycoconjugates such as sulfated glycoproteins into the endolymphatic lumen. Ganglioside Gm1 is a specialized glycolipid containing one sialic acid molecule, which is generally found in the outer leaflet of the cell membrane. This glycolipid, which is known to be a specific receptor for cholera toxin (CT), acts as a membrane transducer and is involved in the modulation of cell metabolism, growth and regeneration. In the present study we identified Gm1 by studying the distribution of the FITC-labeled CT-subunit B in the ES epithelium of adult guinea pigs. Our findings indicate the presence of this ganglioside in the ES, with a predominant localization in the basolateral aspect of the epithelial cell layer. No detectable differences between ES cell types could be identified, whilst the ES distal and intermediate portions showed more reactivity than the proximal portion. This study, which represents the first description of a lipidic glycoconjugate component in the ES, provides evidence in support of the role of the ES in the turnover and regulation of inner ear fluids.