In this task, you are given a sentence and a question, you would be asked to create the answer which is contained in the sentence provided.
Q: Sentence: Complement proteins proteins bind to the surfaces of microorganisms and are particularly attracted to pathogens that are already tagged by the adaptive immune system. Question: Which proteins bind to the surfaces of microorganisms and are particularly attracted to pathogens that are already tagged by the adaptive immune system?
A:
complement proteins