Xenoreactive refers to an immune response against foreign substances or antigens. Some synonyms for this term include alloreactive, allogeneic, heterologous, and xenogeneic. Alloreactive refers to an immune response between genetically different individuals of the same species. Allogeneic refers to genetically different individuals of the same species, such as organ or tissue transplants. Heterologous refers to antigens derived from different species, while xenogeneic refers specifically to antigens from a different species altogether. These terms are particularly relevant in the field of transplant medicine, where understanding immune responses to foreign tissues and organs is crucial for successful transplantation.