Immunology: Innate Immunity Lecture 13 Immunology: Innate Immunity

Elie Metchnikoff Theorized that there are specialized cells within the body that could destroy invading organisms Studying immature starfish larvae  introduced splinter in larvae, area surrounded by motile cells Reasoned certain cells within body were responsible for ingesting and destroying foreign matter - phagocytes

Immune System Used by our bodies to fend off invaders (microorganisms) Two different immune response systems: Innate Immunity 2. Adaptive Immunity - is able to learn and remember

Figure 16.1 - Overview (1 of 3)

Cells of the Immune System Can move from one part of the body to another, traveling through circulatory systems Always found in normal blood Some play dual functions in both innate and acquired immune response

Where do cells of the Immune System come from? All originate from same type of cell, hematopoietic stem cell, found in bone marrow Induced to develop into different types of cells Some types are already mature when they leave the bone marrow, others differentiate after leaving blood

Cells of the Immune System All immune system cells are called white blood cells, or leukocytes Can be divided into two main groups: Granulocytes Agranulocytes

Granulocytes 1. Neutrophils- professional phagocytes All contain granules filled with chemicals that are important in their function Three types: 1. Neutrophils- professional phagocytes - Granules contain antimicrobial substances and degradative enzymes 2. Eosinophils- granules contain substances toxic to multicellular parasites 3. Basophils and Mast cells- blood cells involved in allergic reactions and inflammation

Agranulocytes 1. Monocytes Macrophages: professional phagocytes - present in virtually all tissues 2. Lymphocytes 3. Dendritic cells

Lymphocytes Natural killer (NK) cells- destroy virus-infected and abnormal cells B lymphocytes and T lymphocytes are involved inadaptive immunity B cells: produce antibody T cytotoxic cells: destroy infected host cells T helper cells: coordinate immune response

Dendritic Cells Found in the skin and other points of pathogen origin They are involved in the activation of acquired immunity

Cell Communication Cells of the immune system must be able to communicate with each other They use cytokines Cytokines bind to surface receptors Then induce change in these cells, such as growth, differentiation, movement or cell death

Cytokines 4 kinds: Chemokines: important in chemotaxis of immune cells Interferons: glycoproteins important in the control of viral infections; also help regulate cells involved in immune response Interleukins: important in innate immunity, inflammation, and adaptive immunity Tumor necrosis factors: help kill tumor cells, initiate programmed cell death (apoptosis)

The Innate Immune Response Includes: Physical, chemical, and microbiological barriers Phagocytosis Inflammation Fever Complement system

Figure 15.3

Physical Barriers Skin: microbes sloughed off along with skin cells Microbes must penetrate several layers Mucous Membranes: produce mucus to trap microbes Most lined with cilia

Figure 15.2

Chemical Barriers Low pH in vaginal and urinary tracts, and stomache Defensins: short antimicrobial peptides, insert into bacterial membranes and form pores Lysozyme: degrades peptidoglycan Interferon: are cytokines that trigger: macrophage activation production of substances to interfere with RNA viral reproduction

Microbiological Barriers Normal Flora: not part of immune system, but are part of first line of defense Protection they provide is considerable Competitive exclusion of invading microbes Produce compounds that are toxic to other bacteria Stimulates immune system, providing a moderate amount of “exercise” to system, thereby enhancing it’s function

Phagocytosis Performed by Neutrophils and Macrophages 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)

Figure 16.6

Figure 16.7 - Overview

Inflammation This is a coordinated response to tissue damage Five signs of inflammation: redness, swelling, heat, pain, and loss of function (sometime present) Vital role of inflammation: destroy injurious agent if possible, contain site of damage, and restore tissue function

Figure 16.8a

Figure 16.8b, steps 1–3

Figure 16.8c, steps 4–6

Figure 16.8d

Fever Higher body temperature occurs as a result of certain cytokines called pyrogens Cytokines carried in bloodstream to hypothalamus Hypothalamus responds by raising temperature

Fever How does raising temperature get rid of microorganisms? It inhibits growth of many pathogens by at least two mechanisms: Elevates temperature above optimum growth temperature Activates and speeds up a number of other body defenses

Complement System Series of proteins that constantly circulate in blood and fluids that bathe tissues When they detect presence of foreign material, cascade of reactions follows Complement proteins activated When activated, cooperate with other host defense systems to rapidly get rid of invader

Figure 16.9 - Overview (1 of 5)