An international research team involving scientists of the University Hospital Bonn (UKB) and the University of Bonn has made an important contribution to understanding the human immune response to poxviruses: The scientists were able to show for the first time that different human cell types recognize poxviruses via different sensors in order to trigger inflammatory responses. At the same time, the team developed the world's first nanobodies that can specifically block the DNA sensor AIM2 – a tool that opens up new possibilities for inflammation and infection research. The paper has now been published in The EMBO Journal.
Poxviruses, such as the historically relevant variola virus (causative agent of smallpox), the vaccinia virus (basis of smallpox vaccination), or the currently relevant monkeypox virus (causative agent of Mpox), have large double-stranded DNA genomes that are released into the cell after infection. The human innate immune system recognizes such DNA as a danger signal and can assemble so-called inflammasomes. These large protein complexes trigger a strong inflammatory response and ultimately controlled cell death. Until now, however, it was unclear which of the two known DNA sensors, AIM2 or NLRP3, actually triggers this alarm pathway in human cells. Previous studies had yielded conflicting results.
Researchers from Bonn and Boston have now solved this mystery. Using specially engineered vaccinia viruses carrying a fluorescent inflammasome reporter, they investigated the responses of various human primary cells. The results revealed a surprisingly clear picture: while human macrophages and skin keratinocytes recognize the viral genome via the AIM2 sensor, monocytes respond via NLRP3 instead. This is the first time it has become clear that the activation of inflammasomes in humans is cell type-specific. “Our immune system distinguishes which alarm pathway is used depending on the cell type,” explains study leader and ImmunoSensation3 member Prof. Florian Schmidt from the Institute of Innate Immunity at the UKB. “This specialization was not previously known".
In order to clearly demonstrate these processes, the team developed AIM2-specific nanobodies for the first time. Nanobodies are tiny antibody fragments that function within cells. The AIM2-specific nanobodies bind directly to a crucial domain of AIM2 and prevent the sensor from forming the filaments necessary for inflammasome formation. Bivalent variants, in which two nanobodies are linked, showed a particularly strong inhibitory effect. Produced in genetically modified vaccinia viruses, they block the AIM2 alarm pathway during the infection itself. With the help of this trick, investigations could also be carried out in very short-lived cells such as monocytes, which were isolated from human blood in the laboratory. The researchers were thus able to clearly demonstrate that certain cell types react exclusively via AIM2, while others function independently of it. “These nanobodies are a completely new tool for precisely investigating the role of AIM2 in infections and inflammatory diseases,” says Prof. Schmidt, who is also a member of the Transdisciplinary Research Area (TRA) „Life and Health“ at the University of Bonn.
The study also shows that monkeypox virus (MPXV) can activate inflammasomes in human skin cells and immune cells, albeit to a lesser extent than vaccinia virus. This suggests that MPXV may be better able to evade certain immune responses, which is important for the analysis of current outbreaks.
The new findings provide a significantly improved understanding of how the human body recognizes DNA viruses and which inflammatory mechanisms play a role in this process. In the long term, they may help to develop targeted therapies against dysregulation of the immune system, as they occur in autoimmune diseases or chronic inflammation. In addition, the nanobodies and reporter viruses developed open up new experimental possibilities for international infection research.
Funding
In addition to the University of Bonn and the University Hospital Bonn, Harvard Medical School was also involved in the study. The study was funded by the German Research Foundation (DFG) (TRR237, Emmy Noether Program, Cluster of Excellence EXC2151) and the Boehringer Ingelheim Foundation (Rise Up!).
Publication
Yonas M. Tesfamariam et al.: oxvirus dsDNA genomes differentially activate AIM2 or NLRP3 inflammasomes in human primary cells; DOI: 10.1038/s44318-025-00690-z.
Contact
Prof. Florian Schmidt
Institute of Innate Immunity, University Hospital Bonn
TRA “Life and Health”, University of Bonn
florian.schmidt@ukbonn.de
