Sneezing, scratching and swelling are common signs of allergic reactions. Their triggers can vary widely and include specific foods, bee stings or even sunlight. Yet, many allergies share an underlying mechanism: a surge in Immunoglobulin E (IgE) antibodies, produced by immune cells known as B cells. For some people, this bodily overreaction to otherwise harmless substances can lead to fatal anaphylactic shocks.
Key parts of the allergic response are NF-κB proteins: regulators of gene expression that help activate molecular pathways leading to inflammation.
“When B cells meet an antigen, NF-κB pathways are triggered, causing the cells to crowd together in structures known as germinal centres (GCs). From these, B cells which produce the highest affinity antibodies eventually emerge,” explained co-first authors of the study, Dhakshayini Chanthi Morgan, and Biyan Zhang, a Senior Research Fellow at the A*STAR Singapore Immunology Network (A*STAR SIgN).
Scientists have known that NF-κB signalling is mediated by the p52 protein and a common binding partner, Relb. Together, the protein pair binds to DNA to promote transcription of downstream genes.
“However, previous studies showed that the deletion of p52 but not Relb in mice still crippled the production of certain antibodies,” Morgan said. This suggested that p52 could have an additional, previously unrecognised partner—suspected to be ETS1, a protein previously found to bind p52 in cancer cells, as confirmed in studies by A*STAR Institute of Molecular and Cell Biology (A*STAR IMCB) Distinguished Principle Scientist Vinay Tergaonkar and colleagues.
To study the role of the p52-ETS1 protein complex in allergic responses, NFkB experts Morgan and Tergaonkar teamed up with immunologists led by Kong Peng Lam, Executive Director at A*STAR SIgN, together with his research fellow, Biyan Zhang. The study also involved colleagues from A*STAR SIgN and A*STAR IMCB, as well as collaborators from the National University of Singapore; University of California at San Diego, US; University of Osaka, Japan; and University of Macau, China.
The researchers first created a mouse model with p52 protein mutations that disrupted its interactions with ETS1. Using this new ‘p52 knock-in’ mouse, the team found that disruption of the p52-ETS1 complex in B cells affected their ability to seed GCs, as they were unable to upregulate critical proteins. Importantly, the p52-ETS1 complex also proved necessary for B cells to produce antibodies such as IgE.
Next, the team injected serum samples from allergen-sensitised p52 knock-in mice into wildtype mice. Typically, this would transfer an allergy from an allergic mouse into an unaffected one, as the injected serum would contain allergen-specific IgE.
“We were very excited to see a near-complete lack of GC formation in recipient mice, and consequently a lack of anaphylactic response,” said Morgan.
The team confirmed this through a skin anaphylaxis assay, where sera from wildtype and p52 knock-in mice were injected into the left and right ears of recipient mice. When exposed to the allergen and a blue indicator dye used to visualise allergic reactions, only the left ears of the mice turned blue, validating the team’s hypothesis.
“Since the p52-ETS1 protein complex is necessary to produce the antibodies behind anaphylaxis, blocking the interaction between p52 and ETS1 represents a promising therapeutic approach to mitigating deadly allergic responses,” explained Zhang.
The A*STAR-affiliated researchers contributing to this research are from the A*STAR Singapore Immunology Network (A*STAR SIgN) and A*STAR Institute of Molecular and Cell Biology (A*STAR IMCB).
