Unit 4 AOS 1 – Responding to Pathogens KEY TERMS

Pathogen

Agent that causes disease (e.g., bacteria, virus, fungus, parasite).

Antigen

Molecule that triggers an immune response.

Antibody

Y-shaped protein that binds specifically to an antigen.

Innate immunity

Non-specific first-line and second-line defence mechanisms.

Adaptive immunity

Specific, acquired immune response with memory cells.

B lymphocyte

Produces antibodies and forms plasma and memory cells.

T lymphocyte

Involved in cell-mediated immunity (helper and cytotoxic types).

Clonal selection

Activation and replication of specific B or T cells when antigen binds.

Vaccine

Preparation containing antigen that induces artificial active immunity.

Immunological memory

Rapid secondary response due to memory cells.

Apoptosis

Programmed cell death essential for development and immune regulation.

Cytokine

Signalling protein that coordinates immune responses.

Autoimmune disease

Immune response against self antigens.

Immunodeficiency

Failure of the immune system to respond effectively.