Final answer:
Host defense failure refers to an inadequate response of the immune system, including insufficient cytokine production, while host disease involves excessive or misdirected immune responses such as in hypersensitivity reactions.
Step-by-step explanation:
The fundamental difference between host defense failure and host disease revolves around whether the immune system is compromised or is responding aggressively and inappropriately. Host defense failure pertains to the inadequate response of the immune system, which can occur due to various reasons, including insufficient production of cytokines like TNFa and IFNy. This is crucial in fighting off pathogens such as Y. pestis, where a proper immune response with adequate cytokine production is essential.
In contrast, host diseases, also known as hypersensitivity reactions, arise when the immune system's response is excessive or misdirected, leading to tissue damage and disease. This can be seen in situations where the immune system reacts against self-antigens, leading to autoimmune diseases, or in allergies, where an environmental antigen provokes an exaggerated immune response.