Final answer:
Autoimmunity is an immune response against the body's own cells and tissues, often caused by the immune system's inability to distinguish between self and foreign antigens, leading to disorders where B cells may attack healthy cells. It differs from allergies like pollen reactions, which are immediate hypersensitivity responses.
Step-by-step explanation:
Autoimmunity refers to an immune reaction whereby the body's immune system mistakenly identifies and attacks its own cells and tissues. The correct answer to the question of what defines autoimmunity is b) Immune response against self. Autoimmune disorders are characterized by a breakdown in the immune system's ability to distinguish 'self' from 'non-self,' leading to an immune response that attacks normal body cells. This is a contrast to an allergy to pollen, for example, which is classified as d) immediate hypersensitivity, where the immune system reacts to seemingly harmless substances from outside the body.
Some autoimmune diseases are associated with molecular mimicry, where exposure to pathogens with antigens similar to the body's molecules causes the immune system to later recognize the body's cells as pathogens. B cells are often implicated in these autoimmune responses as they may lose tolerance for 'self', resulting in tissue damage and altered organ function.