Humoral effector molecules: The protein produced by differentiated B cells that specifically binds antigen is called what?

Introduction / Context:
Antibodies (immunoglobulins) are key soluble mediators of the adaptive immune system, enabling neutralization, opsonization, complement activation, and immune memory readouts in diagnostics.

Given Data / Assumptions:

• B cells differentiate into plasma cells that secrete antigen-specific immunoglobulins.
• We need the correct term for the protein that binds antigen.

Concept / Approach:
Immunoglobulins (IgG, IgM, IgA, IgE, IgD) share a Y-shaped structure with variable regions that bind antigen and constant regions that mediate effector functions through Fc receptors and complement.

Step-by-Step Solution:
Map function to term: protein that binds antigen with specificity → antibody.Eliminate generic or incorrect terms: phagocyte and leukocyte are cell types; vaccines are preparations that elicit an immune response.Select antibody.

Verification / Alternative check:
Serological tests (e.g., ELISA) directly detect antigen-specific antibodies produced by B lineage cells.

Why Other Options Are Wrong:

• Phagocyte/Leukocyte: refer to cells, not the protein effector.
• Vaccine: an immunization tool, not an antibody.

Common Pitfalls:
Using “antigen” and “antibody” interchangeably; confusing cellular categories with protein mediators.

Final Answer:
antibody