Question

Which cytokine activates macrophages?

• A. IL-8
• B. IFN-gamma
• C. PAF
• D. Leukotriene B4

Hint:

Which Th1/NK-cell cytokine drives classical (M1) macrophage activation?

Answer 1

The Correct Option is B

Step 1: Macrophage activation is central to chronic inflammation and cell-mediated immunity. Two pathways exist: classical activation (M1) and alternative activation (M2).

Step 2: Classically activated (M1) macrophages are switched on by microbial products and, most importantly, by the cytokine IFN-gamma released from T cells and NK cells. Once activated, M1 macrophages produce reactive oxygen species, nitric oxide, lysosomal enzymes, IL-1 and IL-12, and carry out microbicidal and pro-inflammatory functions. This makes IFN-gamma the classic macrophage-activating cytokine.

Step 3: The distractors are not macrophage activators. IL-8 is a chemokine that recruits and chemoattracts neutrophils. PAF (platelet activating factor) causes vasodilation, increased permeability and platelet aggregation. Leukotriene B4 is a potent neutrophil chemoattractant and aggregating agent. None of these classically activate macrophages.

Step 4: Therefore IFN-gamma is the cytokine that activates macrophages.