A group of protective plasma proteins designated by the letter C and a number are all part of the system.

The group of protective plasma proteins you are referring to is known as the complement system. It is a vital part of the immune system and consists of a series of small proteins found in blood plasma. These proteins are designated by the letter "C" followed by a number, such as C1, C2, C3, and so on.

Roles of the Complement System:

1. Opsonization: Complement proteins can bind to pathogens, marking them for destruction by phagocytes.
2. Chemotaxis: Certain complement proteins recruit immune cells to the site of infection or inflammation.
3. Lysis of Pathogens: The complement system can form a membrane attack complex (MAC) that creates pores in the membranes of pathogens, leading to their lysis.
4. Enhancing Antibody Responses: Complement can interact with antibodies to enhance the body’s immune response.

The complement system can be activated via three pathways: the classical pathway, the lectin pathway, and the alternative pathway, each playing a significant role in immunity and inflammation. This complex interplay contributes significantly to the body’s defense mechanisms against infections and contributes to the inflammatory response.