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An 8-year-old boy develops fever, chills, and night sweats. In addition, he feels nauseated and has vomited on several occasions. The diagnosis of influenza infection is made. You would expect endogenous viral proteins to be presented primarily by which of the following?
A. Major histocompatibility complex class I molecules
B. Major histocompatibility complex class II molecules
C. Macrophages
D. Dendritic cells
E. B cells
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Choice (A) is the correct answer. Endogenous antigens such as viral proteins are degraded by virus-infected cells and are presented on the cell surface by major histocompatibility complex (MHC) class I molecules. CD8+ cells, including cytotoxic T cells (TC), recognize the antigen/MHC class I complex, and through a complex serious of interactions and cell signaling pathways, the TC cells become activated and differentiate into cytotoxic T lymphocytes which are able to destroy virus-infected cells. Exogenous antigen, on the other hand, is presented primarily by MHC class II molecules (Choice B). Macrophages (Choice C) are phagocytic cells and also antigen presenting cells. They are derived from monocytes. Dendritic cells (Choice D) are the most efficient antigen presenting cells. B cells (Choice E) differentiate into antibody-secreting plasma cells and memory cells.
