A team led by researchers at the Garvan Institute of Medical Research has pinpointed individual cells that cause cryoglobulinemic vasculitis, an autoimmune disease characterized by severe inflammation of blood vessels. They also uncovered how these cells go rogue by evading checkpoints that normally stop immune cells from targeting the body's own tissues.
"Current treatments for autoimmune disease address only the symptoms, but not the cause. To make more targeted treatments that address disease development and progression, we first need to understand the cause," says Professor Chris Goodnow, co-senior author of the work published today in Cell.
"We have developed a technique that allows us to look directly at the cells that cause autoimmune disease—it's as though we're looking through a new microscope lens for the first time, learning more about autoimmune disease than was ever possible before."
Because rogue immune cells are so rare in a blood sample—less than one in 400 cells—studying them has been a challenge. Analysis to date has at best revealed averages of the vast mix of cells in a patient's sample, says Mandeep Singh, first author of the published paper.
"Using cellular genomics, we developed a method to “zoom in” on these disease-causing immune cells in the blood samples of four patients with cryoglobulinemic vasculitis," says Dr Singh. By first separating individual cells, and then separating their genetic material, the researchers isolated immune cells that produced rheumatoid factors—antibody proteins that target healthy tissues in the body and are associated with the most common autoimmune diseases.
Once isolated, the researchers then analyzed the DNA and messenger RNA of each of these rogue cells, scanning more than a million positions in the genome to identify DNA variants that may be at the root of disease. Through their analysis, the researchers discovered that the disease-causing immune cells of the vasculitis patients had accumulated a number of mutations before they produced the damaging rheumatoid factors. "We identified step-wise genetic changes in the cells at the root of an autoimmune disease for the first time, tracing an evolutionary tree of how normal immune cells develop into disease-causing cells," explains co-senior author Joanne Reed.
Remarkably, the researchers found that some of the first gene mutations that occurred in these rogue cells were known to drive lymphomas. "We uncovered 'lymphoma driver mutations', including a variant of the CARD11 gene, which allowed the rogue immune cells to evade immune tolerance checkpoints and multiply unchecked," explains Professor Goodnow. Further, the researchers found that cells with the lymphoma driver mutations accumulated further mutations that caused the rheumatoid factors they produced to aggregate, or clump together, at lower temperatures.
"This explains the patients' cryoglobulinemic vasculitis, a severe condition that develops in some people with Sjögren's syndrome, systemic lupus, rheumatoid arthritis, or hepatitis C virus infection. In these individuals, rheumatoid factors in the blood aggregate at colder temperatures closer to the skin and also in the kidneys, nerves, and other organs, which damages blood vessels and often proves very difficult to treat," adds Reed.