Final answer:
The group of serum proteins other than antibodies that enhance innate immune responses is called the complement system, consisting of about 20 proteins that support phagocytosis, inflammation, and cell lysis.
Step-by-step explanation:
The group of serum proteins that stimulate phagocytosis, inflammation, and cell lysis, other than antibodies, is known as the complement system. This system consists of an array of approximately 20 soluble proteins that are part of the innate immune system. These complement proteins work by enhancing the phagocytosis of pathogens, boring holes in the pathogens to cause cell lysis, and recruiting lymphocytes. Additionally, they work synergistically with antibodies to enhance the adaptive immune response, particularly through a process known as complement fixation, where the combination of antibodies and complement proteins promotes the rapid clearance of pathogens via opsonization.