1. They are expressed only by macrophages and a few other cell types, and are used to present antigen to CD4-cells (Helper) a. Class I MHC proteins b. Class II MHC proteins 2. Insufficiency of C3 leads to? a. Red cell hemolysis b. Incline to infections with pyogenic bacteria c. Incline severity of Neisseria bacteremia d. Sever Persistent pyogenic sinus and respiratory tract infections 3. The _______ is a collection of highly polymorphic genes encoding the proteins that regulate the immune responses. a. Complement b. MHC c. The Immune response.