If a genetically engineered mouse lacks functional MHC class II molecules, which consequence follows regarding its adaptive immune response to a novel bacterial infection?

💡 Explanation

MHC class II molecules are essential for presenting antigens to helper T cells, which then orchestrate other immune responses. Because these molecules are absent, helper T cell activation will be impaired; therefore, option D is correct, rather than options involving cytotoxic T cells or antibody responses that rely on T helper cells.

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