Which would be characteristic of a T-independent antigen?

Which would be characteristic of a T-independent antigen?

• A. The IgG antibody is produced exclusively.
• B. A large number of memory cells are produced.
• C. Antigens bind only one receptor on B cells.
• D. It consists of a limited number of repeating determinants.

Answer: (B)

T-independent antigens activate B cells without helper T cells because their antigens have repeating epitopes that can cross-link many B cell receptors on a single B cell. This strong, multivalent engagement provides enough signal to trigger B cell activation without T cell help, leading to mainly an IgM response with little class switching or affinity maturation, and typically limited memory formation. Among the options, the feature that best fits a T-independent antigen is that it consists of a limited number of repeating determinants. Those repeating units enable extensive cross-linking of B cell receptors, driving activation without T cell help. The other statements don’t align with TI responses: the response is not exclusively IgG, memory production is generally limited, and TI antigens don’t bind to just a single B cell receptor—the repeating determinants enable multiple BCRs to engage.

T-independent antigens activate B cells without helper T cells because their antigens have repeating epitopes that can cross-link many B cell receptors on a single B cell. This strong, multivalent engagement provides enough signal to trigger B cell activation without T cell help, leading to mainly an IgM response with little class switching or affinity maturation, and typically limited memory formation.

Among the options, the feature that best fits a T-independent antigen is that it consists of a limited number of repeating determinants. Those repeating units enable extensive cross-linking of B cell receptors, driving activation without T cell help. The other statements don’t align with TI responses: the response is not exclusively IgG, memory production is generally limited, and TI antigens don’t bind to just a single B cell receptor—the repeating determinants enable multiple BCRs to engage.