As one of the immune dysfunctions, hypersensitivity reactions can be divided into four general categories based on the mechanism of immunological response: (1) immediate or anaphylactic hypersensitivity mediated by IgE, (2) antibody-mediated cytotoxicity mediated by antibodies of the IgM or IgG classes and complement, (3) immune complex hypersensitivity mediated by IgG or IgM classes, and (4) cell mediated or delayed type hypersensitivities. The gene discussed is CD40LG; the disease is immune system disorder.