Increased CD8^dim and Decreased CD8^bright T Cells as Immunological Signature for Multibacilary Leprosy Patients

Leprosy, a chronic infectious disease caused by Mycobacterium leprae, manifests in a spectrum of clinical forms and severity. This study investigated the percentage of CD8⁺ T cells and their subpopulations (CD8^bright and CD8^dim T cells) in leprosy patients stratified by clinical forms, bacterial load, and age. No significant differences were observed in the overall percentage of CD8⁺ T cells among healthy controls and leprosy patients. However, an increased percentage of CD8^dim T cells and a decreased percentage of CD8^bright T cells were associated with severe multibacillary and lepromatous forms of leprosy, independent of bacillary load. Further, these cellular profiles correlated more strongly with disease severity than with age, in spite of elderly multibacillary patients exhibiting significant reductions in CD8^bright T cells and increases in CD8^dim T cells compared to young or middle-aged paucibacillary patients, but not compared to young and middle-aged multibacillary patients. These findings suggest that CD8^bright and CD8^dim T cell profiles are critical indicators of disease progression and severity in leprosy, highlighting their potential as biomarkers for clinical evaluation.