Which of the following is a messenger that mediates the connection between the innate and adaptive immune systems?

Correct Answer: D

Rationale: Cytokines are signaling molecules that bridge innate and adaptive immunity by facilitating communication, such as activating lymphocytes after innate detection of pathogens.

Correct Answer: A

Rationale: Macrophages perform phagocytosis, kill bacteria, and present antigens to T cells, key roles in innate immunity.

Correct Answer: C

Rationale: The effector phase is when activated immune cells eliminate the antigen.

Correct Answer: C

Rationale: MHC is a gene cluster encoding proteins for antigen presentation, distinct from BCR and TCR genes.

Correct Answer: D

Rationale: With different parental HLA genes, an individual inherits 3 class I (HLA-A, B, C) and 3 class II (HLA-DR, DP, DQ) per parent, totaling about 12 unique MHC molecules.