Final answer:
Blood proteins that combine with pathogens to protect the body are called antibodies, which are specific Y-shaped proteins that target antigens for immune response. The complement system also assists antibodies in pathogen destruction by marking and destroying them with a cascade of protein actions.
Step-by-step explanation:
Proteins in the blood that combine with pathogens in order to protect against pathogen invasion are called antibodies. Antibodies, also known as immunoglobulins, are Y-shaped proteins produced by the immune system. These proteins are highly specific and bind to antigens, which are foreign molecules, typically proteins, carbohydrates, lipids, or nucleic acids, that elicit an adaptive immune response. The presence of antibodies specific to a pathogen allows the immune system to target the pathogen for destruction.
There is also a complement system, made up of about 20 proteins, that works alongside antibodies. It attacks pathogens in a cascading fashion to mark and destroy them. The complement proteins are capable of responding immediately to infecting microorganisms, completing the antibody response of the adaptive immune system by coating the pathogens in complement proteins.'