Answer: Any foreign molecule (usually protein/polysaccharide) that triggers an immune response.
- A A specialized type of circulating white blood cell frequently found within lymph nodes and spleen
- B Any foreign molecule (usually protein/polysaccharide) that triggers an immune response
- C An antibody protein produced specifically by activated plasma cells against one pathogen
- D A weakened or otherwise inactivated pathogen preparation frequently used in a vaccine dose
Correct answer: B. Any foreign molecule (usually protein/polysaccharide) that triggers an immune response
Explanation: An antigen is any molecule (usually foreign protein or polysaccharide) that can trigger an immune response and bind specifically to antibodies or T cell receptors. The immune system distinguishes 'self' from 'non-self' antigens.
An antibody is Y-shaped, with two identical antigen-binding sites at the tips of the variable regions - each shaped to recognise one specific antigen - while the constant (Fc) region at the base is recognised by immune cells to trigger further responses.
Concept context
Innate and adaptive immunity, B cells, T cells, antibodies, vaccines, and immune disorders. Critical for NEET.