Leukotriene B4 (LTB4) is an arachidonic acid metabolite that functions as a neutrophil chemoattractant. Other neutrophil chemoattractants include interleukin 8 (IL-8), C5a, and bacterial N-formyl peptides.
The arachidonic acid pathway yields multiple active metabolites including leukotrienes, prostaglandins, thromboxane, and prostacyclin. Lipoxygenase is a key enzyme that metabolizes arachidonic acid into the hydroperoxides which are subsequently metabolized into leukotrienes. LTB4 is a type of leukotriene that functions as a potent neutrophil chemoattractant in addition to mediating neutrophil aggregation and adhesion. Leukotrienes C4, D4, and E4 are other downstream metabolites of lipoxygenase and primarily mediate bronchoconstriction.
Illustration A outlines the arachidonic acid pathway including relevant enzymes and metabolite functions. Note how lipoxygenase catalyzes the formation of hydroperoxides from arachidonic acid, which are further metabolized to LTB4 (neutrophil chemoattractant) and LTC4, LTD4, and LTE4 (bronchoconstrictors).
Answer 1: Interleukin 1 (IL-1) is a pro-inflammatory cytokine produced by multiple immune and epithelial cells that stimulates a widespread inflammatory response. It causes a rise in body temperature (fever) and promotes adhesion factor expression on endothelial cells to enable transmigration of leukocytes to sites of active inflammation.
Answer 2: Interleukin 2 (IL-2) is a pro-inflammatory cytokine produced by CD4 T-cells that induces activation of natural killer (NK) cells, CD4 T-cells, and CD8 T-cells. IL-2 has been used as an anti-cancer therapy because it promotes T-cell and NK cell activation, thereby leading to increased endogenous anti-tumor activity.
Answer 3: Interleukin 4 (IL-4) is a pro-inflammatory cytokine that induces the differentiation of naïve CD4 T-cells to Th2 cells. It also induces B-cell class switching to IgE and increases MHC II production. Excess levels of IL-4 are associated with allergies.
Answer 4: Interleukin 5 (IL-5) is a pro-inflammatory cytokine produced by Th2 cells and mast cells. It mediates eosinophil activation as well as B-cell class switching to IgA.
Lipooxygenase catalyzes the formation of leukotrienes from arachidonic acid. Leukotriene B4, interleukin 8, activated complement component 5 (C5a), and bacterial N-formyl peptides function as neutrophil chemoattractants.