Immune System

(immunus = to be free)

•primary defense against disease-causing organisms

An overview of the body's defenses

Lymphatic System (lympha = clear fluid (Latin)

•consists of lymphatic vessels and lymph organs; lymph capillaries take up excess tissue fluid and return it to the bloodstream•it works with the immune system to help defend the body against disease

The Human Lymphatic System(pharyngealtonsils)

Once lymph fluid enters the lymphatic vessels, it is called lymph.

The capillaries merge to form lymphatic vessels that merge before entering one or two ducts: the thoracic duct or the right lymphatic duct

First Line of Defense – External Barriers

•Skin and Mucus Membranes•Low pH of skin•Saliva and tears contain lysozyme.

Red bone marrow is the site of origin for all types of blood cells, including the five major types of white blood cells:Neutrophils (65%) Lymphocytes (25%) Monocytes (6%) Eosinophils (3%) Basophils (1%)

Never Let Monkeys Eat Bananas!

In a child, most bones have red bone marrow, but in adults it is present only in bones of the skull, sternum, ribs, clavicle, pelvis, and vertebral column.

1) Neutrophils and monocytes, changeshape to squeeze through capillary walls and enter tissue fluid.

2) As they leave the blood and enter the tissues,monocytes differentiate into macrophages.

Second Line of Defense (Non specific Internal Defenses) involvesphagocytic white blood cells.

Phagocytosis by a Macrophage

Macrophage

Bacteria

3) Eosinophils phagocytize and contain a number of destructiveenzymes within the cytoplasmand defend against large parasites.

Antimicrobial Proteins

•Mast cells release histamine, which causes the capillaries to dilate and become permeable, which allows pro-teins to escape into the tissues causing swelling

Histamine is storedin mast cells in connective tissues.

Histamine increasespermeability ofcapillaries

The complement system, is a number of plasma proteins, that attracts (“complements”) phagocytes to the scene; some bind to the surface of pathogens already coated with antibodies

Interferon is a protein produced by virus-infected cells. It binds to receptors of noninfected cells, causing them to prepare for possible attack by producing substances that interfere with viral replication; it is species specific.

A simplified view of the inflammatory response

Natural (NK) Killer Cells kill the body’s infected cells. They have no specificity and no memory.

Immunity is primarily the result of action of B lymphocytes and T lymphocytes. B cells mature in the bone marrow and T cells mature in the thymus gland and move to the blood.

B cells produce antibodies whereas T cells attack cells that produce nonself proteins

Third Line of Defense (pathogen-specific

recognition)

The Development of Lymphocytes

Can become any type of blood cell

Clonal Selection- primary immune response

A plasma cell is a mature B cell that mass-produces antibodies against a specific antigen.

The clonal selection theory states that the antigen selects which lymphocyte will undergo clonal selection and produce more lymphocytes bearing the same type of antigen receptor.

Immunological Memory

Antibodies bind to specific areas of antigens

The Structure of a Typical Antibody Molecule

Characteristics of B Cells•Antibody-mediated immunity against bacteria•Produced and mature in the bone marrow•Reside in spleen and lymph nodes; circulate in blood and lymph•Directly recognize antigen and thenundergo clonal selectionClonal expansion produces antibody-secreting plasma cells as well as memory B cells

Characteristics of T Cells•Cell-mediated immunity against viruses and cancer cells•Produced in bone marrow; maturein thymus•Antigen must be presented in groove of a MHC molecule•Cytotoxic T cells destroy nonselfprotein-bearing cells•Helper T cells secrete cytokines that control the immune response

The interaction of T cells with MHC molecules

Cell-mediated Immune Response

1) Cytotoxic T Cells can bring about

the destruction of antigen-bearing

cells, such as virus-infected cells

2) Helper T Cells regulate immunity

by secreting cytokines, which are

chemicals stimulating other immune

cells.

Effector Mechanisms of Humoral Immunity

Opsonization:bound antibodiesenhance macro-phage attachment or phagocytosisof microbes

How Antibodies Work:

•agglutination (clumping) – makes it easier for phagocytes to eat•neutralization – blocking sites on an antigen•precipitation – phagocytes ingest•complement (proteins) – get activated by antibodies

An Overview of Acquired Immune Response

Specialized Lymphocytes Attacking a Cancer Cell

A Cytotoxic T Cell Has Lysed a Cancer Cell

Cytotoxic (Killer) T Cell

An Overview of the Immune Responses

A T cell Infected with HIV (gray particles)

HIV on a Lymphocyte

Detail of HIV on Lymphocyte

Compare and contrast B cell and T cell action.

Immune System:

Name one component of each of the three lines of defense.

How are antigens related to antibodies?

How do interferons protect the body against viruses?

How is lymph returned to the bloodstream?

Name two places where whiteblood cells are highly concentrated.