So, I've just started my journey into the world of immunology and I'm already having trouble understanding a basic concept regarding complement proteins and their pathways. I understand the differences between the pathways, but for some reason cannot get something straight. When C4 levels are low, does this cause C3 to remain low through all the pathways? Also, If the complements are low, does this imply that the person will be more susceptible to bacterial and viral infections? Thanks in advance for any help.