Biology » The Immune System » Innate Immune Response

Summarizing Innate Immune Response


The innate immune system serves as a first responder to pathogenic threats that bypass natural physical and chemical barriers of the body. Using a combination of cellular and molecular attacks, the innate immune system identifies the nature of a pathogen and responds with inflammation, phagocytosis, cytokine release, destruction by NK cells, and/or a complement system. When innate mechanisms are insufficient to clear an infection, the adaptive immune response is informed and mobilized.



leukocyte that releases chemicals usually involved in the inflammatory response

B cell

lymphocyte that matures in the bone marrow and differentiates into antibody-secreting plasma cells

complement system

array of approximately 20 soluble proteins of the innate immune system that enhance phagocytosis, bore holes in pathogens, and recruit lymphocytes; enhances the adaptive response when antibodies are produced


chemical messenger that regulates cell differentiation, proliferation, gene expression, and cell trafficking to effect immune responses


leukocyte that responds to parasites and is involved in the allergic response


protease that enters target cells through perforin and induces apoptosis in the target cells; used by NK cells and killer T cells


an organism that is invaded by a pathogen or parasite


localized redness, swelling, heat, and pain that results from the movement of leukocytes and fluid through opened capillaries to a site of infection

innate immunity

immunity that occurs naturally because of genetic factors or physiology, and is not induced by infection or vaccination


cytokine that inhibits viral replication and modulates the immune response


leukocyte that is histologically identifiable by its large nuclei; it is a small cell with very little cytoplasm


large phagocytic cell that engulfs foreign particles and pathogens

major histocompatibility class (MHC) I/II molecule

protein found on the surface of all nucleated cells (I) or specifically on antigen-presenting cells (II) that signals to immune cells whether the cell is healthy/normal or is infected/cancerous; it provides the appropriate template into which antigens can be loaded for recognition by lymphocytes

mast cell

leukocyte that produces inflammatory molecules, such as histamine, in response to large pathogens and allergens


type of white blood cell that circulates in the blood and lymph and differentiates into macrophages after it moves into infected tissue

natural killer (NK) cell

lymphocyte that can kill cells infected with viruses or tumor cells


phagocytic leukocyte that engulfs and digests pathogens


process that enhances phagocytosis using proteins to indicate the presence of a pathogen to phagocytic cells


an agent, usually a microorganism, that causes disease in the organisms that they invade

pathogen-associated molecular pattern (PAMP)

carbohydrate, polypeptide, and nucleic acid “signature” that is expressed by viruses, bacteria, and parasites but differs from molecules on host cells

pattern recognition receptor (PRR)

molecule on macrophages and dendritic cells that binds molecular signatures of pathogens and promotes pathogen engulfment and destruction


destructive protein that creates a pore in the target cell; used by NK cells and killer T cells

T cell

lymphocyte that matures in the thymus gland; one of the main cells involved in the adaptive immune system

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