It is notoriously one of the most complex systems in the natural world, but its complexity is there for good reason. By guarding against and responding to foreign microbes, our immune system keeps us alive. Primary immunodeficiency disorders, characterized by defects in the immune system, turn every infection into a life-threatening one.
This was the scenario that challenged clinicians Enrica Tan, Woei Kang Liew, Ah Moy Tan and colleagues at the KK Women’s and Children’s Hospital (KKH): a one-week-old baby was hospitalized for a variety of infectious diseases that required urgent antimicrobial treatment.
“When doctors from KKH admitted an infant patient with recurrent infections alongside lung, skin and liver damage, they recruited scientists at A*STAR’s Institute of Molecular and Cell Biology (IMCB) to help determine the cause of this unprecedented disease and devise a treatment strategy,” said John Connolly, a Research Director at IMCB and co-corresponding author on the study with KKH’s Liew.
The team was quick to recognize that they were dealing with a primary immunodeficiency disorder: a novel heterozygous mutation in the NFKBIA gene that appeared to be unlike any other NFKBIA mutation.
“Mutations in NFKBIA are normally characterized by defective T and B cell responses,” Connolly explained. “But the NFKBIA mutation we found caused pathological changes in myeloid cell cytokine production.”
NFKBIA encodes a protein called IκBα, which inhibits the activation and transport of the NF-κB protein complex. Whole-exome sequencing confirmed that the missense mutation occurred at a site on the IκBα protein critical for its degradation. As the mutation prevented IκBα degradation, it caused severe defects in downstream NF-κB signaling and cytokine production.
“We believe the mutation acts in two parts. Firstly, it limits immune responses in fibroblasts and macrophages, via the suppression of pro-inflammatory cytokines IL-6 and TNFα,” said Connolly. “Secondly, it fails to limit immunopathological responses, over-producing IL-1β which increases neutrophil activity, causing liver damage and inflammation.”
Functional and phenotypic characterization of the patient’s white blood cells revealed an abnormally high production of a key pro-inflammatory cytokine, IL-1β. Replicating the mutation in mice and myeloid cells differentiated from the patient’s induced pluripotent stem cells confirmed that this mutation was the cause of IL-1β hyper-production.
With the genetic cause pinpointed, the team decided on a treatment strategy. A bone marrow transplant temporarily stabilized the patient’s condition, but the re-emergence of the patient’s white blood cells sent IL-1β levels soaring again. Treatment with anakinra, a recombinant IL-1 receptor antagonist, briefly halted disease progression but had to be withdrawn due to side effects.
Although unable to save the patient, the researchers made the important discovery of a rare mutation and the role of IκBα in IL-1β production. These findings have implications for the development of treatments against liver disease and cancer that target the NF-κB pathway, Connolly added.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Molecular and Cell Biology (IMCB), the Singapore Immunology Network (SIgN) and the Institute of Medical Biology (IMB).
