A young child undergoes implantation of a cardiac pacemaker. During surgery, the physician must remove the thymus. If this child encounters an antigen requiring B-cell-Tcell collaboration, they will to mount an immune response. These antigens are thus called

Correct Answer: C

Rationale: Thymectomy prevents T cell development, impairing responses to thymus-dependent antigens.

Correct Answer: D

Rationale: Dendritic cells are key antigen-presenting cells delivering antigens to secondary lymphoid tissues.

Correct Answer: D

Rationale: IgM has low affinity due to its pentameric structure and initial response role.

Correct Answer: C

Rationale: Low pH in the GI tract (e.g., stomach acid) is an innate barrier.

Correct Answer: A

Rationale: C1 is the initiating protein in the classical pathway, binding to antibodies.