Ultrasensitive ELISA Enables Detection of Interferon
By Labmedica International staff writers
Posted on 02 May 2017
Image: A scanning electron micrograph (SEM) showing how the single-molecule array digital ELISA is carried out in tiny, femtoliter-volume wells containing beads capable of binding single molecules (Photo courtesy of Rodero MP et al).
Researchers have developed a method for ultrasensitive detection of interferon alpha protein linked to multiple autoimmune diseases, including systemic lupus erythematosus (SLE) and dermatomyositis. The technique will aid the diagnosis and treatment, and has also begun to reveal differential levels and cellular sources among different autoimmune diseases.
Inappropriate activation of interferon signaling can cause the immune system to attack healthy, uninfected self-tissues. Elevated interferon signaling is linked, for example, to complex autoimmune disorders such as SLE, dermatomyositis, and diabetes mellitus. Mutations in individual genes can also abnormally activate interferon signaling and cause a class of autoimmune diseases known as type I interferonopathies. Being extremely potent, even small changes in interferon- levels can have dramatic effects on the immune system.
Diagnosing these diseases and understanding the role of interferon- proteins in their pathology have been largely hampered by the inability to directly measure the low levels of these proteins in patient samples. A team of researchers led by Darragh Duffy from the Pasteur Institute (Paris, France) and Yanick Crow from the Institut Imagine (Paris, France) developed an ultrasensitive method to detect minute amounts of interferon- in human blood or cerebrospinal fluid.
Their method is based on a technology called single-molecule array digital ELISA, which can identify individual antibody-labeled proteins. Using high-affinity anti-interferon- antibodies isolated from patients with the syndrome called APECED, the researchers were able to detect interferon- at attomolar concentrations, equivalent to just quadrillionths of a gram per milliliter. This is 5,000 times more sensitive than existing methods for detecting these proteins.
The team was able to measure interferon- levels in the blood of healthy, SLE, dermatomyositis, and type I interferonopathy patients. As expected, levels were elevated in all of the autoimmune samples. Furthermore, in SLE patients, higher interferon- levels correlated with an increased severity of disease. They also detected elevated interferon- levels in the cerebrospinal fluid of patients infected with viral meningitis.
Interferon- levels were particularly high in patients with type I interferonopathies. By isolating individual types of blood cells, the team discovered that mutations in a gene STING cause elevated production of interferon- in monocytes and plasmacytoid dendritic cells. These cells were not affected in patients with SLE, dermatomyositis, or other type I interferonopathies, suggesting that the source of interferon- can vary depending on the autoimmune disease.
"The ultrasensitive detection of interferon- protein in human material can provide novel insights into disease-causing pathways," said co-senior author Prof. Duffy, "It also allows the direct measurement of interferon protein as a disease biomarker for patient stratification and for monitoring the efficacy of treatments such as the antiinterferon signaling therapies that are currently being tested."
The researchers described their method in a new “Technical Advances” format for reporting a novel technique that advances preclinical or clinical research and where authors validate the new technique and demonstrate its advantage over existing approaches.
The study, by Rodero MP et al, was published April 18, 2017, in the Journal of Experimental Medicine.