Multiple choice Which of the following complement proteins are anaphylotoxins? C3a, C4a, C5a C1a, C2a, C3a C1b, C2b, C3b C3b, C4b, C5b Reveal answer Fill a bubble to check yourself A Correct answer Explanation C3a, C4a and C5a proteins are anaphylotoxins. They cause smooth muscle contraction.