Immune System

IMMUNE SYSTEM

Immune System • collection of mechanisms within an organism that protects against infection by identifying and killing pathogens. • a network of cells, tissues, and organs that work together to defend the body against attacks by “foreign” invaders

Major Components : • • • •

Bone marrow = source of WBC’s Thymus = where T lymphocytes mature Lymphatic vessels = carry lymph Lymph nodes = where immune cells congregate • Spleen = compartments where immune cells gather and work • Tonsils, adenoids, Peyer’s patches and appendix

IMMUNITY = the condition of being immune or resistant to a particular infectious disease = the body’s capability to repel foreign substances and cells

NON-SPECIFIC DEFENSE MECHANISMS

First Line of Defense • Skin = completely covers all other parts of the body • Mucous membranes = mucus entraps invaders • Cilia (post. nasal membranes, nasal sinuses, bronchi and trachea

• digestive enzymes acidity of the stomach bile • saliva, sweat and tears • urine • microbial antagonism

Second Line of Defense • FEVER ( T = 38◦C ) - stimulated by PYROGENS a. external = pathogens b. internal = interleukins - augments host defenses by: 1. stimulates wbc’s to deploy and destroy invaders 2. reduces available free plasma iron 3. induces production of IL-1

• IRON BALANCE - wbc’s produce IL-1 w/c stimulates iron storage in the liver reducing free iron for the pathogens • CELLULAR SECRETIONS a. Interferons = small anti-viral proteins produced by virus-infected cells b. Fibronectin = epithelial tissue secretion that blocks bacterial attachment

c. Β lysin = polypeptide released from pletelets during infection d. Interleukins = polypeptides secreted by macrophages and lymphocytes • BLOOD PROTEINS a. Complement = a group of 30 different proteins in blood plasma = constitutes the “complement system”

Consequences of Complement Activation: 1. Initiation and amplification of inflammation 2. Chemotaxis = attraction of phagocytes to the sites to w/c they are needed 3. Activation of leukocytes 4. Lysis of bacteria and other foreign cells 5. Opsonization = increased phagocytosis by phagocytic cells = phagocytosis facilitated by deposition of opsonins on the surface

b. Prostaglandins - membrane associated lipids acting like local hormones - controls platelet aggregation, inflammation, immune response, pain production, etc.

• PHAGOCYTOSIS

2 most important phagocytes: 1. NEUTROPHILS (granulocytes) = most efficient and abundant 2. MACROPHAGES = from monocytes a. wandering – leave the bloodstream b. fixed – remain in tissues and organs

PHAGOCYTOSIS

Steps in Phagocytosis: 1. 2. 3. 4.

CHEMOTAXIS ATTACHMENT INGESTION DIGESTION

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INFLAMMATION = a complex series of events as the body responds to any local injury, irritation, microbial invasion, or toxins

Purposes of Inflammation: 1. Localize an infection 2. Prevent spread 3. Neutralize toxins 4. Aid in repair of damaged tissue

THIRD LINE OF DEFENSE

“Immune response to disease”

Properties of an Ideal VACCINE • With enough antigens • With antigens from all strains of a pathogen • Not too toxic • Doesn’t cause disease

Types of Vaccines A. Artificial Active

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Live (attenuated) viruses Ex. Measles, OPV, MMR

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Dead (inactivated) viruses Ex. Hepa B, influenza, rabies

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Live (attenuated) bacteria Ex. BCG

• Dead (inactivated) bacteria Ex. Anthrax, cholera • Bacterial capsular antigens Ex. Hib (H. influenza type B) • Bacterial toxoids Ex. tetanus

B. Artificial Passive Human gamma globulins/ pooled immune serum globulins Ex. HBIg (Hepatitis B) TIg (Tetanus) Rig (Rabies)

IMMUNOLOGY = scientific study of immune responses

ANTIGENS - foreign organic substance large enough to stimulate production of antibodies “should be foreign to the human body” ex. microorganisms

ANTIBODIES - glycoproteins produced by lymphocytes in response to the presence of an antigen - formed by B lymphocytes - “immunoglobulins” Factors affecting Antibody production: 1. Nature of antigen 2. Site of antigenic stimulus 3. Amount of antigen 4. Frequency of exposure

Five classes of Immunoglobulins: • IgA - 15-20% of Igs in human serum - in tears, saliva, colostrom etc • IgD - less than 1% on serum Igs - large amounts on B cell surfaces • IgE - less than 1% in serum but in large amounts in basohils and mast cells (allergy)

• IgG - 70 to 75% of the total Ig pool - smallest and can cross the placenta • IgM - 10% of the serum Ig pool - largest Ig and the first to be formed in the primary response to antigens - most efficient complement fixing Ig

• Agammaglobulinemia = inability to produce antibodies • Hupogammaglobulinemia = produce insufficient amounts of Abs • Immunosuppressed = unable to make Abs following chemotherapy or immunosuppressive drug injection

IMMUNE RESPONSES

Humoral Immunity = “antibody-mediated immunity” = involves antibody production

Cell-mediated Immunity = complex system of interactions between many types of cells and cellular secretions

HYPERSENSITIVITY •

Defensive immune responses becomes overly sensitive

Types of Hypersensitivity Reactions: A. Immediate ( Type I, II, III) = few minutes to 24 hours B. Delayed (Type IV) = after 24 hours

• Type I HR (anaphylactic reaction) - involves IgE Ex. Asthma, hives, food allergies • Type II HR (cytotoxic reaction) - involves IgG or IgM Ex. Transfusion reactions Rh incompatibility • Type III HR ( immune complex reaction) - involves IgG and IgM Ex. Serum sickness autoimmune diseases (SLE)

• Type IV HR (delayed type hypersensitivity) Ex. Tuberculin test transplant rejection

Immunodeficiency • ACQUIRED = caused by drugs and certain infections

• INHERITED = treated with bone marrow transplant Ex. Chediak-Higashi synd. Wiskott-Aldrich synd.

Med. Tech IMMUNOLOGY & SEROLOGY

LYMPHOCYTE EFFECTOR FUNCTION antigen – antibody complexes Humoral Immunity

1. 2. 3. 4.

Precipitation Agglutination Neutralization Opsonization

5. Antibody dependent cytotoxicity 6. Complement activation 7. Immediate hypersensitivity Cell Mediated Immunity 1. Delayed hypersensitivity 2. Cell mediated lysis

IMMUNOLOGIC MEMORY primary immune response secondary immune espose memory cells – greater number and thus shorter response time (isotype switch) vaccination

Regulation of Immune Response - immune system goes awry autoimmunity Mechanism that deal with potentially self reactive lymphoytes(B and T cells)

 SELECTIVE NONRESPONSIVENESS OR TOLERANCE  REGULATORY T CELLS  REGULATING CYTOKINES