In the complement system, which function is attributed to C5a in the immune response?

In the complement system, which function is attributed to C5a in the immune response?

• A. Upregulate integrin
• B. Neutrophil chemotaxis
• C. Lyses microbes by MAC
• D. Activates T cells

Answer: (B)

C5a acts as a powerful chemoattractant in the complement system, drawing neutrophils to sites of infection and activating them to fight microbes. This chemotactic effect is its defining role in the innate immune response, which is why neutrophil chemotaxis is the best answer. MAC lysis is driven by C5b forming the membrane attack complex, not by C5a. Activating T cells is not the primary function of C5a in the immediate innate response, though it can modulate broader immune activity. Upregulating integrins on leukocytes can assist adhesion and migration, but the hallmark function described in this context is the recruitment of neutrophils via chemotaxis.

C5a acts as a powerful chemoattractant in the complement system, drawing neutrophils to sites of infection and activating them to fight microbes. This chemotactic effect is its defining role in the innate immune response, which is why neutrophil chemotaxis is the best answer.

MAC lysis is driven by C5b forming the membrane attack complex, not by C5a. Activating T cells is not the primary function of C5a in the immediate innate response, though it can modulate broader immune activity. Upregulating integrins on leukocytes can assist adhesion and migration, but the hallmark function described in this context is the recruitment of neutrophils via chemotaxis.