<prompt> Which one of the following is the best neutrophil and macrophage attractant?C5aVariable region of the heavy chain of IgGJ chainHLA-A  <response>: 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. 