The most significantly altered lymphocyte subsets in IBM that exhibited the greater increase consisted of highly activated T cells, including CD4+ T‐bet+, CD8+CD57+, CD8+ T‐bet+, CD8+ IFNγ+ Perforin+, CD8+ Perforin+, Natural killer T (NKT) cells, Treg Foxp3+ and CD8+CD28−, while Vδ2+, CD56lowCD16bright, Vγ9+Vδ2+, Treg Ki67+, naïve CD8+ T cells and NK cells were the most reduced subsets. The gene discussed is PRF1; the disease is inclusion body myositis.