Immunoglobulins and the Immune System

Role of IgE-FcεR1 in Pathological Cardiac Remodeling and Dysfunction

BACKGROUND

Immunoglobulin E (IgE) belongs to a class of immunoglobulins involved in immune response to specific allergens. However, the roles of IgE and IgE receptor (FcεR1) in pathological cardiac remodeling and heart failure are unknown.

METHODS

Serum IgE levels and cardiac FcεR1 expression were assessed in diseased hearts from human and mouse. The role of FcεR1 signaling in pathological cardiac remodeling was explored in vivo by FcεR1 genetic depletion, anti-IgE antibodies, and bone marrow transplantation. The roles of the IgE-FcεR1 pathway were further evaluated in vitro in primary cultured rat cardiomyocytes and cardiac fibroblasts (CFs). RNA sequencing and bioinformatic analyses were used to identify biochemical changes and signaling pathways that are regulated by IgE/FcεR1.

RESULTS

Serum IgE levels were significantly elevated in patients with heart failure as well as in 2 mouse cardiac disease models induced by chronic pressure overload via transverse aortic constriction and chronic angiotensin II infusion. Interestingly, FcεR1 expression levels were also significantly upregulated in failing hearts from human and mouse. Blockade of the IgE-FcεR1 pathway by FcεR1 knockout alleviated transverse aortic constriction- or angiotensin II-induced pathological cardiac remodeling or dysfunction. Anti-IgE antibodies (including the clinical drug omalizumab) also significantly alleviated angiotensin II-induced cardiac remodeling. Bone marrow transplantation experiments indicated that IgE-induced cardiac remodeling was mediated through non-bone marrow-derived cells. FcεR1 was found to be expressed in both cardiomyocytes and CFs. In cultured rat cardiomyocytes, IgE-induced cardiomyocyte hypertrophy and hypertrophic marker expression were abolished by depleting FcεR1. In cultured rat CFs, IgE-induced CF activation and matrix protein production were also blocked by FcεR1 deficiency. RNA sequencing and signaling pathway analyses revealed that transforming growth factor-β may be a critical mediator, and blocking transforming growth factor-β indeed alleviated IgE-induced cardiomyocyte hypertrophy and cardiac fibroblast activation in vitro.

CONCLUSIONS

Our findings suggest that IgE induction plays a causative role in pathological cardiac remodeling, at least partially via the activation of IgE-FcεR1 signaling in cardiomyocytes and CFs. Therapeutic strategies targeting the IgE-FcεR1 axis may be effective for managing IgE-mediated cardiac remodeling.

Bacterial attachment to oropharyngeal epithelial cells in breastfed newborns

On day 2 post partum, swab samples were obtained from the oropharyngx of 20 healthy, breast-fed babies. The samples were examined for aerobes (culture on agar plates), for bacterial coating with the immunoglobulins SIgA, IgG and IgM (immunofluorescence assay), for bacterial attachment to epithelial cells (fluorescence microscopy of acridine orange stained material, and scanning electron microscopy). alpha-Hemolytic streptococci grew almost exclusively in the oropharynx, while 32% (median value) of the epithelial cells showed bacterial attachment in abundance, viz. > 50 attached bacteria per cell, 66% (median value) of the bacteria showed positive reactivity when treated with anti-human SIgA serum. 72% (median value) of the bacteria were coated with IgG, but no IgM coating of the bacteria could be detected. Newborns do not possess IgA antibodies, as only IgG is able to pass the placental barrier. The SIgA-rich colostrum is capable of coating the oropharyngeal bacteria of breast-fed babies during their first days after birth. However, despite abundant SIgA-coating, bacteria still succeed in attaching to the epithelial cells of the oropharynx. This finding hints that factors other than SIgA impede the bacterial/cellular adhesion mechanism.

Secretory IgA- and IgG-coated bacteria in chronically discharging ears

SIgA- and IgG-coated bacteria obtained from 17 discharging middle ears (14 patients, 9 male, 5 female, age range from 1 to 79 years) were evaluated using an immunofluorescence assay. Simultaneously, quantitative and qualitative bacteriological analyses of the middle ear effusions (MEEs) were performed. MEEs containing Staphylococcus aureus harboured bacteria which were intensely coated with both SIgA and IgG antibodies. In contrast, MEEs containing Pseudomonas aeruginosa displayed minimal, if any, SIgA- and IgG-coated bacteria. Two young patients harboured bacteria (Haemophilus influenzae and S. aureus/Streptococcus pneumoniae, respectively) which were heavily coated with IgG, but not with SIgA. Immunoglobulin-coating of bacteria involved in otitis media is of the utmost importance in eradication of the infection.