"Ir Gene" stands for the immune response gene, which is responsible for regulating the immune response in individuals against pathogenic microbes. There are several synonyms for the term "Ir Gene," including "MHC," which stands for the major histocompatibility complex and is responsible for presenting antigens to T cells; "H-2 complex," primarily found in mice, and "HLA complex," present in humans. The Ir gene is further categorized into class I and class II genes, with the former playing a crucial role in identifying and targeting infected cells by cytotoxic T cells, whereas the latter helps in initiating an immune response by recruiting and activating other immune cells. Understanding the different synonyms for the Ir Gene is essential for better comprehension of immune responses and potential applications in therapeutic interventions.