Question

Which of the following are the major roles of C3a and C5a in the ultimate destruction of microbes by the complement pathway (select all that apply)? Please explain

a. Increase expression of complement protein receptors on phagocytic cells

b. Downregulate expression of complement receptors on phagocytes

c. Cleavage of C3 and C5 proteins

d. Recruit neutrophils and monocytes to site of infection

e. Enhance movement of antigen presenting cells to lymph nodes

Answer 1

C3a and C5a are produced from the complement pathway by the cleavage of C3 and C5 respectively. Both of these are anaphylatoxins and play a role in inducing inflammation.

They act on receptors present on several immune cells like mast cells, monocytes, neutrophils and antigen-presenting cells. These receptors CR3 for C3a and CR5 for C5a. Binding to these receptors and their concentration gradient from the site of infection triggers the neutrophils and monocytes to the site of infection. It also triggers the antigen-presenting cells to the lymph nodes where they can activate an immune response.

The binding of the ligands C3a and C5a furthere triggers a transcriptional change in the cell that increases the expresion of the receptors. This allows the cells to become more sensitive to the presence of these ligands thereby allowing them to be recruited quickly.

Therefore, the correct answers are a, d and e.