Adaptive Immunity – Humoral (antibody-mediated) mechanisms
Adaptive Defenses Overview
Adaptive Immune (Specific Defense) System: A highly specialized and complex defense system within the body.
Primary Functions:
Protects against infectious agents (e.g., bacteria, viruses) and abnormal body cells (e.g., cancer cells).
Amplifies the inflammatory response, enhancing its effectiveness.
Activates the complement system, a group of proteins that can directly lyse pathogens or mark them for destruction.
Key Characteristics:
Priming Required: Must be initiated by an initial exposure to a specific foreign substance. This priming takes time.
Specific: Recognizes and targets particular antigens, distinguishing between different pathogens or abnormal cells.
Systemic: Not confined to the initial site of infection; its effects can be observed throughout the entire body.
Memory: Possesses the ability to remember previously encountered antigens, leading to stronger and faster attacks upon subsequent exposures.
Two Overlapping Arms:
Humoral (antibody-mediated) immunity: Involves B lymphocytes and circulating antibodies.
Cellular (cell-mediated) immunity: Involves T lymphocytes acting directly against target cells.
Adaptive Immunity: Humoral vs. Cell-Mediated
Humoral Immunity:
Mechanism: Antibodies are produced by B lymphocytes (B cells).
Circulation: Antibodies circulate freely in the body fluids (e.g., blood plasma, lymph).
Action: Binds temporarily to the target cell or foreign substance.
Outcome: Temporarily inactivates the target and marks it for destruction by phagocytes or the complement system.
Targets: Primarily has extracellular targets (e.g., bacteria, extracellular viruses, toxins).
Cell-Mediated Immunity:
Mechanism: T lymphocytes (T cells) act directly against target cells.
Action: Can kill infected cells directly or indirectly.
Directly: By lysing (killing) virus-infected cells or cancer cells.
Indirectly: By releasing chemicals (cytokines) that enhance the inflammatory response or activate other lymphocytes or macrophages.
Targets: Primarily has cellular targets (e.g., virus-infected cells, cancer cells, cells of foreign grafts).
Antigens
Definition: Substances that can mobilize adaptive defenses and provoke an immune response. They are the targets of all adaptive immune responses.
Characteristics: Most are large, complex molecules not normally found in the body (thus,