<unk> , in a general sense, is the<unk>  of an observed agent which initiates reactions outside the main reaction expected. This has implications for any kind of test or assay, including diagnostic tests in medicine, and can be a cause of false positives. In immunology, the definition of<unk>  refers specifically to the reaction of the immune system to antigens. There can be<unk>  between the immune system and the antigens of two different pathogens, or between one pathogen and proteins on non-pathogens, which in some cases can be the cause of allergies.
Cross-reactivity
Antibiotic synergy
Opportunistic infection
Parasitism
Peripheral tolerance
Drug resistance
Immunogenicity
Vaccine resistance