The innate immune system provides the first line of defense using physical and biochemical barriers like the skin and mucous as well as phagocytes that engulf pathogens. The adaptive immune system has a more targeted response using B cells that produce antibodies and T cells that recognize pathogens. There are five main types of antibodies - IgG, IgA, IgM, IgD, and IgE - that help neutralize, immobilize, and eliminate antigens through activation of the complement system or enhancement of phagocytosis.