The X chromosome contains a number of genes involved in the regulation of innate and adaptive immune responses, including TLR7, TLR8, IRAK1, IL2RG, FOXP3 and CD40L. Studies targeting sex-related differences of immune responses investigated effects mediated by the number of X chromosomes and delivered an increased risk for the development of SLE with growing numbers of X chromosomes. The gene discussed is TLR7; the disease is systemic lupus erythematosus.