USMLE Step 1 Question of the Day!

There is a minor alteration of MHC-I antigens when a cell is invaded by a virus. The immune system will not recognize the infected cell without the help of alpha and beta interferon inducing increased class I antigen expression on the cell’s surface. Which of the following is the source of interferon-beta?

A) fibroblasts
B) T cells
C) B Cells
D) Macrophages
E) Natural killer cells


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A) fibroblasts. Fibroblasts release interferon-beta and interleukin-6 in response to viral infection. IL-6 stimulates B cells to release interferon-alpha which also has antiviral activity. The increased expression of MHC-I antigens on infected cells surfaces helps the immune system recognize viral infected cells from healthy ones.