Neutralizing anti-interleukin-23 is associated with opportunistic infections, according to a study published in The New England Journal of Medicine. Steven M. Holland, MD, and colleagues screened patients, most of whom had thymoma, known to have anti-interleukin-12 for autoantibodies against interleukin-23. The study team also tested a second cohort of patients with and without thymoma or known anti-interleukin-12 with unusual infections. Half of the 30 patients with anti-interleukin-12 who had severe mycobacterial, bacterial, or fungal infections had antibodies that neutralized interleukin-23. The researchers noted a correlation between the potency of neutralization and the severity of infection but found no association between the neutralizing activity of anti-interleukin-12 alone and infection. The presence of anti-interleukin-23 was associated with infection status in 81% of the validation cohort of 91 patients with thymoma. Overall, Dr. Holland and colleagues detected neutralizing anti-interleukin-23 in 26% of patients with thymoma and 83% with disseminated, cerebral, or pulmonary infections. Anti-interleukin-23 was present in 19% of patients with severe intracellular infections and 12% with unusual intracranial infections. The study results “should lead to the design of new diagnostic tests and therapeutic approaches based on anti-interleukin-23 autoantibodies in patients with rare and severe infections of unknown cause,” the researchers wrote in an accompanying editorial.