Which class of cell surface molecules is recognized by CD8+ cytotoxic T lymphocytes, presenting endogenous cytoplasmic antigens processed by the proteasome?

Answer and explanation

Correct answer: B. MHC Class I

  1. Step 1: Recall the lymphocyte co-receptor interaction rule: the product rule ( and ) dictates that CD8 interacts with MHC Class I, while CD4 interacts with MHC Class II.
  2. Step 2: MHC Class I molecules consist of an heavy chain paired with -microglobulin, are expressed on all nucleated cells, and present endogenous cytoplasmic peptides (viral or abnormal self-antigens) degraded by the immunoproteasome and transported via TAP into the ER.
Answer
MHC Class I.
Why not the others: MHC Class II is expressed selectively on professional antigen-presenting cells (dendritic cells, macrophages, B cells) and presents exogenous antigens to CD4+ T helper cells; CD40 ligand is expressed on activated CD4+ T cells to promote B cell class switching; Toll-like Receptor 4 is a pattern-recognition receptor that recognizes lipopolysaccharide (LPS) from Gram-negative bacteria.

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