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:

1. 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:

1. Granulocytes

2. Agranulocytes

Granulocytes

• 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: 1. Chemokines: important in chemotaxis of

immune cells2. Interferons: glycoproteins important in the

control of viral infections; also help regulate cells involved in immune response

3. Interleukins: important in innate immunity, inflammation, and adaptive immunity

4. 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:

1. Elevates temperature above optimum growth temperature

2. 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)