The two types of light chains are:

Correct Answer: D

Rationale: The two types of immunoglobulin light chains are lambda (λ) and kappa (κ).

Correct Answer: B

Rationale: Mutations in both RAG-1 and RAG-2 prevent T and B cell development, but NK cells remain unaffected.

Correct Answer: A

Rationale: The TCR is the primary antigen recognition molecule on T cells.

Correct Answer: D

Rationale: DRα has the fewest alleles among MHC class II genes.

Correct Answer: C

Rationale: Systemic lupus erythematosus is associated with HLA-DR3.