Immune System

Chapter 21

Nonspecific Defenses• Species resistance - docking sites

on cells only allow certain pathogens to attach. Ex: you can’t get:–Tobacco mosaic virus

–Dutch elm disease

–Distemper

• Mechanical & Chemical Barriers–1st Line of Defense

•Skin and mucous membranes

•Stomach - HCl

•Tears - lysozyme

•Hair

–2nd Line of Defense

•Inflammation – chemotactic proteins

•Phagocytosis – macrophages and neutrophils

–Natural Killer Cells – tumor cells and cells with viral infections

–Interferon – anti-viral proteins

–Complement Proteins – causes lysis of antigen

–Fever

White blood cells (WBC) are released

• Monocytes, macrophages, neutrophils, eosinophils, natural killer cells

a. Blood vessels expand near the wound or entry.

b. Swelling occurs (caused by histamine) which increases body temperature to kill off pathogens

c. Basophils released

2nd line of defense: Inflammatory Process

Specific Cellular Defenses• Overview of Immune Response

–Humoral Immunity

•Provided by antibodies

•Produced by lymphocytes

•Bind to bacteria and free floating viruses

–Cell Mediated Immunity

•Special lymphocytes direct the attack of infected cells

•Attack cancer cells, parasites, transplants

•Release chemicals to mediate OR stimulate other parts of the immune system

–Antigens•Large molecules that interact and respond to cells and immune chemicals

–Antibodies •Native antigens; immunoglobulins

• Humoral Immunity (B-Cell Immunity)

•Produced in the bone marrow

•Produce antibodies

•Stimulated by antigens and/or lymphokines

•2 types of B cells

–Plasma cells – make antibodies (2000/sec) and memory cells

–Memory cells – remain for a lifetime to produce more antibodies if antigen returns

• Antibodies

–5 classes

–IgD – attached to B cells; act as a receptor sites

–IgM – RBC, food and bacterial markers; stimulates complement proteins; agglutinating agent

–IgG – main antibody; tissue marker, virus, bacteria and toxin antibody

–IgA – found in milk, tears, urine, sweat; prevents attachment of pathogens to epithelial tissues

–IgE – associated with allergies; cause release of histamine

•Responsible for 1o and 2o immune response

–1o - initial exposure to antigen, plasma cells produce antibodies; lag time

–2o – subsequent exposure to previous antigen; produce 1000’s of antibodies within hours

–Types of Antibody Immunity

•Acquired Immunity

–Active artificial – vaccine of the antigen (measles); requires boosters

–Passive artificial – vaccine of antibodies from another infected animal (rabies)

•Natural Immunity–Active natural – get the disease; lifetime immunity

–Passive natural – mother’s antibodies are passed to fetus prior to birth; short-term

• Cell-Mediated Immunity–T cells

•Originate and mature in the thymus

•Must become “tolerant” to body’s own proteins so as not to react to them

•Can only recognize an “antigen” when it is bound to another immune cell

•Secrete “lymphokines” to stimulate cloning of other immune cells

•4 types:–Cytotoxic (killer) T cells – secrete “perforin” which lyses target cells

–Helper T cells – direct cloning of other T & B cells through secretion of lymphokines

–Suppressor T cells – dampens activity of killer & helper cells

–Delayed hypersensitivity T cells – play role in allergies and chronic inflammation

Organ Transplants

• 4 Types of transplants (grafts)–Autografts – self to self; always successful

–Isografts – identical twins; always successful

–Allografts – same species; used most often; complications due to tissue typing

–Xenografts – different species; rarely successful

• Following transplantation

–Anti-inflammatory drugs

–Cytotoxic drugs

–Radiation

–Cyclosporin to suppress production of interleukins, Helper T and Cytotoxic T cells without stopping production of already sensitized B cells

• Rejection

–Early – inadequate blood supply to graft

–Late – burst of unexplained antibodies

Homeostatic Imbalances

• Immunodeficiencies

• Autoimmunity

• Hypersensitivities – body responds to a harmless antigen–Immediate hypersensitivity- within minutes

–Cytotoxic hypersensitivity – transfusion reactions

–Immune-complex hypersensitivity – strep, malaria, chronic viral infections; cause rashes, swollen lymph nodes

–Delayed hypersensitivity – poison ivy, cosmetics