This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'A scientist  working in the laboratory on the mechanisms involved in inflammation. He observes that the leucocytes leave the blood vessels and move towards the site of bacteria. Which of the following is likely to mediate this movement of the bacteria? \nSelect and explain. \nA. C3a, B. C5a, C. Histamine, D. C3b', 'role': 'user'}, {'content': 'Answer: B \nExplanation: After exiting the circulation, leukocytes move in the tissues toward\xa0 the site of injury by a process called chemotaxis, which is defined as locomotion along a chemical gradient. Both exogenous and endogenous substances can act as chemoattractants, including the following:\n\nBacterial\xa0 products,\xa0 particularly\xa0 peptides\xa0 with\xa0 N- formylmethionine termini.\nCytokines, especially those of the chemokine family.\nComponents of the complement system, particularly C5a.\nProducts\xa0of\xa0the\xa0lipoxygenase\xa0pathway\xa0of\xa0arachidonic acid (AA) metabolism, particularly leukotriene B4 (LTB 4).\n\nReference-Robbins BASIC PATHOLOGY 10th edition pg-65', 'role': 'assistant'}]