If HIV infection is characterized by adipose tissue CD8+ T cell enrichment without pronounced macrophage recruitment, this may reflect the need for a costimulatory factor in obese adipose tissue to recruit macrophages in the presence of CD8+ T cells, may indicate that cytokine expression profiles of adipose tissue CD8+ T cells differ in obesity and HIV infection, or reflect another as yet unknown mechanism. The gene discussed is CD8A; the disease is obesity due to melanocortin 4 receptor deficiency.