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: Microbiology
Which one of the following is the best neutrophil and macrophage attractant? 
Select and explain. 
A. C5a, B. Variable region of the heavy chain of IgG, C. J chain, D. HLA-A
A: C5a
Answer: A: C5a 
Explanation: C5a is a component of complement. Activation of complement by endotoxin, or antigen antibody complexes produces C5a, which is a neutrophil and macrophage attractant. The variable region of the heavy chain of IgG is not known as the best neutrophil or macrophage attractant. The J moiety of IgM and IgA does not possess chemotactic propeies for neutrophils and macrophages. HLA-A and HLA-B are genes for the human leucocyte antigens (HLA). Ref: Levinson W. (2012). Chapter 63. Complement. In W. Levinson (Ed), Review of Medical Microbiology & Immunology, 12e.