PDCD1 and systemic lupus erythematosus: More than 30 SNPs have currently been identified in the human PD-1 gene [14], and several of them have been proven to be associated with the susceptibility of numerous diseases, including systemic lupus erythematosus (SLE), rheumatoid arthritis, ankylosing spondylitis, allergic bronchial asthma, type 1 diabetes, multiple sclerosis, acute anterior uveitis, chronic hepatitis B virus infection, subacute sclerosing panencephalitis, antisperm antibody-related infertility and cancers [12, 13, 15–23].