Ans: A (B4) Ref: Ammthanarayan R. Paniker CKJ. Textbook of Microbiology, 8th Edition. Hyderabad: Universities Press: 2009. Pg. 165Explanation:LeukotrienesA substance originally demonstrated in lungs, producing slow, sustained contraction of smooth muscles, and therefore termed slow reacting substance of anaphylaxis (SRS-A), has since been identified as a family of leukotrienes (LTB4, C4, D4, E4).LTB4 is a potent mediator of leukocyte movement both in vitro and in vivo. It mediates interaction of neutrophils (PMNs) w ith vascular endothelial cells.