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Resistance and the Immune System: Innate Immunity

Chapter 19

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• Blood Cells Form an Important Defense for Innate and Acquired Immunity

• Major Components• Serum is the fluid part of blood, containing:

• Minerals, salts, proteins, etc.• Plasma is serum that contains clotting agents• Cells

• RBC• Platelets• Leukocytes (white blood cells)

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• Leukocytes (white blood cells) are produced in the bone marrow• Neutrophils

(polymorphonuclear leukocytes [PMNs]) are phagocytes

• Eosinophils contain toxic compounds to defend against multicellular parasites

• Basophils are similar to mast cells, acting in allergic reactions

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• Monocytes are phagocytes that mature into macrophages in tissue

• Lymphocytes move to the lymph nodes after maturation• Natural killer (NK) cells destroy

virus-infected and abnormal cells

• B lymphocytes and T lymphocytes are involved in acquired immunity

• Dendritic cells are found in the skin and other points of pathogen origin• They are involved in acquired

immunity

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• Lymphoid organs are the site of maturation, development and proliferation of lymphocytes

• The primary lymphoid tissues are the thymus and bone marrow

• The secondary lymphoid tissues are the spleen and lymph nodes• The spleen contains cells

that monitor and fight infectious microbes

• The lymph nodes contain phagocytes and lymphocytes

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• The interactions between innate and acquired immunity make infections and disease establishments difficult

• Innate immunity (nonspecific resistance) is genetically-encoded to recognize common pathogenic features and foreign substances; host’s “early-warning system”• Skin, interferon, lysozyme, phagocytes• Cytokines are chemical signals sent

by many immune cells to tissues involved with initiating acquired immunity; released by defensive cells in response to an activating substance (pathogen)

• Acquired immunity (specific resistance) involves production of:

• Antibodies, action of complement System, Cellular immunity, Killer T-lymphocytes

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• Species Immunity: disease affecting one species will not affect another

• Behavioral Immunities: exist among various races and people of the world (related to a people’s way of life)

• Racial Immunities: reflect the evolution of resistant humans

• Population Immunities: some parasites adapt to certain body environment

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• Mechanical barriers• Skin: breaches of the skin may

allow microbes to enter the blood

• Mucous membranes

• Chemical Barriers• pH: acidity• Defensins: antimicrobial

peptides found in secretions• Lysozyme: tears, saliva, sweat• Interferons: interfere with viral

reproduction

• Microbiological barriers: normal microbiota

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• Phagocytosis is the capture and digestion of foreign particles

• Chemokines are cytokines that attract macrophages and neutrophils to infected tissues

• Opsonins attach to microbes to increase the ability of phagocytes to adhere (opsonization)

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• Low to moderate fever supports the immune system by:• inhibiting rapid microbial growth• encouraging rapid tissue repair• heightening phagocytosis

• Pyrogens are cytokines produced by:• some leukocytes• fragments from pathogens

• They affect the hypothalamus, causing elevated body temperature

• If a temperature rises above 40°C in an adult, host metabolic inhibition can occur• This can cause convulsions and

death

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• NK cells are formed in the bone marrow, and migrate to: tonsils, lymph nodes and spleen

• When activated, they produce cytokines that trigger response by macrophages and other cells

• They move into blood and lymph where they kill cancer cells and virus-infected cells

• Not phagocytic, contain on their surfaces special receptors capable of forming cell-to-cell interactions with a target cell• Cytolytic mediators: perforins,

granzymes

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• Complement is a series of proteins that circulate in the bloodstream that represents another innate defense to disease.• They activate in the presence of microbes in a

cascade of steps that assist inflammatory response and phagocytosis.

• In the classical pathway, antibody-microbe complexes activate complement proteins that activate C3 convertase

• In the alternative pathway, the complement protein C3 binds to the pathogen cell surface to activate C3 convertase

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• The immune system responds to pathogens by rapid immune response followed by development of antibodies and lymphocytes to generate acquired immune response.

• Pathogen-associated molecular patterns (PAMPs) help the innate immune system recognize pathogens by identifying unique microbial molecular sequences not found on host cells.

• Toll-like receptors (TLRs) are signaling receptors on: macrophages, dendritic cells and endothelial cells

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• TLRs mediate a specific response to distinct PAMPs

• They stimulate the secretion of cytokines, • For example, those

that stimulate production of acute phase proteins

• The TLR response must be regulated to prevent infection and immune disorders