Comprehensive investigations in mice have suggested that a population of NK-cells, uniquely expressing the IL-6 receptor alpha and colony-stimulating factor 1 receptor (IL6Ra+Csf1r+), induced via IL-6/STAT-3 (signal transducer and activator of transcription-3) signalling, accumulate with obesity within visceral adipose tissue (95). This evidence concerns the gene IL6R and obesity due to melanocortin 4 receptor deficiency.