New pathway in immune defense discovered

Bonn researchers decode the interaction of monocytes and platelets in human blood

Monocytes, a special type of white blood cell, secrete cytokines as inflammatory messengers that are crucial for an appropriate immune response. Researchers at the University Hospital Bonn (UKB) and the University of Bonn have now discovered that platelets, also known as thrombocytes, communicate with monocytes and increase their inflammatory capacity. By understanding the platelet-monocyte interaction, they hope to improve the treatment of immune disorders and associated diseases. The results of the study have now been published in the renowned journal “EMBO Molecular Medicine” and will be featured on the cover of August issue.

Monocytes are white blood cells, known as leukocytes. They are an important part of the innate immune system and contribute to host defense in the blood by secreting large quantities of pro-inflammatory cytokines. Abnormal activity of monocytes leads to hyperinflammation, i.e. very severe inflammation, as well as life-threatening cytokine storms. On the other hand, disturbed monocyte function is associated with “immune paralysis”. In this condition, the immune system’s ability to fight off invaders such as viruses and bacteria is inhibited. This increases susceptibility to infections. “It is therefore crucial to understand how the functions of monocytes are regulated,” says senior and corresponding author Prof. Dr. Bernardo Franklin from the Institute of Innate Immunity at the UKB and the Cluster of Excellence ImmunoSensation2 at the University of Bonn, explaining the motivation to investigate the role of platelets in the regulation of monocyte-induced inflammation.

Platelets play a central role in blood clotting, but are also thought to perform important functions in the immune system. Prof. Franklin’s research team has already identified platelets as an important regulator of inflammation. They now report that a low platelet count in the rare blood disorder immune thrombocytopenia (ITP) or the artificial removal of platelets from healthy monocytes results in “immunoparalysis”. This is characterized by a disturbed cytokine reaction and is an immunological challenge. “Remarkably, supplementing monocytes with fresh platelets reverses this condition and restores the monocyte cytokine response,” says corresponding and co-first author Dr. Ibrahim Hawwari, a postdoctoral fellow of the University of Bonn at the Institute of Innate Immunity at the UKB. […]

Participating Core Facilities: The authors acknowledge the support from the Flow Cytometry and Microscopy Core Facilities. Furthermore, staff of the Translational Proteomics Core Facility is affiliated with this study.

Participating institutions and funding:

Institute of Innate Immunity, Medical Faculty, University of Bonn, Bonn, Germany

Institute of Clinical Chemistry and Clinical Pharmacology, University Hospital Bonn, University of Bonn, Bonn, Germany

Department of Medicine III, University Hospital Bonn, Bonn, Germany

Department of Pediatrics, Division of Pediatric Infectious Diseases, GuerinChildren’s, Cedars Sinai Medical Center, Los Angeles, CA, USA

Infectious and Immunologic Diseases Research Center (IIDRC), Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, CA, USA

Funding for this project was provided by the European Research Council, the HORIZON Lump SumGrant, as well as Germany’s Excellence Strategy from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation).

Publication: I. Hawwari et al: Platelet transcription factors license the pro-inflammatory cytokine response of human monocytes; EMBO Molecular Medicine; DOI: 10.1038/s44321-024-00093-3