A possible explanation may be found in the study by Chioma et al., which has found that the cell cycle inhibitory molecule programmed death-1 is significantly upregulated on CD4+ T cells in females with sarcoidosis, which promoted fibrotic reactions, thus causing fibrosis-related cardiac complications in this population (Abstract: Chioma OS, Celada LJ, Abel K, Newcomb DC, WP Drake. Here, CD4 is linked to sarcoidosis.