Systemic lupus erythematosus (SLE), or lupus, shows a marked sex bias, affecting about nine females for every one male, according to Susan Kovats, PhD, who studies sex differences in immunity at the Oklahoma Medical Research Foundation in Oklahoma City. This characteristic of lupus suggests that hormones are involved in the pathogenesis of the disease. It also suggests, Dr. Kovats said, that the X chromosome might play a role.
Though studies since the 1970s have indicated a significant role for hormones, the issue is still complex and not well understood, and relatively little research has been done on the molecular mechanisms that might be responsible. This may be because of difficulties with influencing the immune system in vitro, said George A. Robinson, PhD, of University College London’s Centre for Rheumatology.
Dr. George A. Robinson
But Dr. Robinson and his team found a unique way of investigating the role of sex chromosomes and hormones in the inflammatory profiles across subjects of different sex, gender, age, and disease status. In research published online in The Lancet Rheumatology, Dr. Robinson and his team looked at immune cells taken from both cisgender men and women and transgender men and women, and thus were able to “get a more physiological view of what sex hormones are doing to the immune system,” he said.
Dr. Kovats agreed that it was a useful approach. “The transgender people provided an opportunity to effectively separate sex hormone levels from chromosome content,” she said in an interview.
Methods and findings
Peripheral blood mononuclear cell (PBMC) samples were taken from cisgender individuals with and without juvenile-onset lupus and assessed for 28 immune-cell subsets, including different T-cell, B-cell, and monotype subsets. Subjects included 39 postpubertal cisgender men and women (17 men and 22 women) who did not have juvenile-onset lupus, and 35 postpubertal cisgender men and women (12 men and 23 women) who did have juvenile onset lupus. All were aged 16-25 years. The transgender group included five transgender men and five transgender women (aged 18-19) who were undergoing gender-affirming sex hormone treatment.
The analysis found that one of the key differences between young postpubertal cisgender men and age-matched cisgender women was that the men had significantly elevated frequencies of regulatory T cells (T-reg cells), and the T-reg cells from young cisgender men had greater suppressive capacity in vitro than did those from cisgender women. In addition, RNA sequencing data from isolated T-reg cells showed the transcriptomic signature of the cisgender men’s T-regs were significantly enriched for genes in the P13K-AKT signaling pathway. The frequency of T-reg cells was not influenced by sex hormones, but their transcriptomic profile was affected.
“These results are beginning to give us an indication of which genes might be differentially regulated by sex hormones and how these are associated with autoimmunity,” Dr. Robinson said. “We’ve also found that, depending on whether you’re a cisgender man or woman, you may have a different pathogenic process to developing lupus. It’s not necessarily that one mechanism drives the disease across both sexes.”