The complement system consists of a series of proteins that can attach to pathogens and mark them for destruction by other immune cells.
Adaptive immunity involves specific recognition of antigens by lymphocytes, leading to clonal expansion and memory T and B cells that can respond quickly upon reexposure to the same antigen.
Innate immunity provides an immediate defense against pathogens through physical barriers such as skin and mucous membranes, chemical defenses like acidic pH and enzymes, and cellular responses including phagocytes and natural killer cells.
