The Immune System

Ch. 21

The Immune SystemCh. 21

Body Defenses· 2 intrinsic systems

1. innate (nonspecific) defensesdoes not discriminate between

one threat or anotherfirst line of defense - skin and

mucous membranessecond line of defense -

phagocytes, NK cells, inflammation, antimicrobial proteins, fever

2. adaptive (specific) defenseprotect against specific threatsthird line of defense - B and T cells

Innate Defenses· prevent the approach, deny the entrance, or limit the spread of pathogens

harmful or disease-causing microorganisms· present at birth· rapid response (same every time)

Surface Barriers· skin, mucous membranes and their secretions· keratin resistant to microorganisms, weak acids/bases, bacterial enzymes, and toxins

nicks and cuts allow organisms to invade· mucous membrane secretions

acidic secretions - sweat, sebum, vaginal secretions, tears

HCl - stomachsaliva - contains lysozymemucus - respiratory and

digestive systems

Internal Defenses· phagocytes - move between cells and recognize chemical antigens that stimulate phagocytosis

carried out by macrophages (type of monocyte) and neutrophils· natural killer (NK) cells - lymphocytes that "polices" the body looking for cells lacking "self" antigens

induce apoptosis (programmed cell death) and release chemicals that enhance inflammation (cytokines)· inflammation - triggered by physical trauma, intense heat, irritating chemicals, or infection by viruses, fungi, or bacteria

4 cardinal signs - redness, heat, swelling, painprevents the spread of damaging agents to nearby

tissuesdisposes of cellular debris and pathogensprevents movement to encourage healing/repair

Internal Defenses· antimicrobial proteins

interferons - proteins released from virus-infected cells that trigger the production of antiviral proteins that interfere with viral replication inside healthy cells; mobilize the immune system

complement - lyses microorganisms, enhances phagocytosis, intensifies inflammatory and immune responses· fever - abnormally high temperature

initiated by pyrogens (chemicals released by leukocytes and macrophages)

high body temp inhibits microbial multiplication (iron and zinc stored in liver) and enhances body repair processes

The Immune System

1 All of the following are innate defenses EXCEPTA complement proteins

B inflammation

C mucous membrane secretions

D antibodies

E NK cells

2 MATA: Which innate defenses involve an increase in temperature?

A complement

B fever

C inflammation

D interferons

3 Innate defenses, like fever and interferons, are nonspecific and acquired throughout our lifetime.

True

False

Adaptive Defenses· characteristics

specificity - recognizes and reacts to specific antigensversatility - not restricted to the first infectionmemory - mounts stronger attacks on "remembered"

antigenstolerance - can ignore "self" antigens

· typescell-mediated immunity (T cells) - cells killing cellsantibody-mediated (humoral) immunity (B cells) -

antibodies mark pathogens for destruction

Cell-Mediated Immunity· T cells cannot recognize antigens in their natural state; can only recognize processed or internalized antigens· target cells infected by viruses and bacteria, abnormal or cancerous cells, and cells of transplanted foreign tissue· activated T cells release cytokines (chemical messengers), like interferon or interleukins, that amplify and regulate immune responses· T cell differentiation

helper T (TH) - "director" of adaptive immune responseactivate B cells, T cells, and macrophages, recruit other

immune cells to join the fightAIDS destroys helper T cells (no immune response)

cytotoxic T (TC) - attack and kill other cellsregulatory R (TREG) - suppress response of B and T cells

The Immune System

MHC = Major Histocompatability Complex

Cell-Mediated Immunity Antibody-Mediated Immunity Antibody-Mediated Immunity· starts with antigen challenge

first encounter between an immunocompetent B cell and its antigen; activates B cell

immunocompetence - ability to recognize a specific antigen· activated B cells divide and produce plasma cells· plasma cells secrete antibodies

2000/sec for 4 or 5 days· antibodies bind with their specific antigen, marking it for destruction

form antigen-antibody complexesPLAN: precipitation (falling out of solution), lysis

(complement activation), agglutination (clumping), neutralization (blocks toxic effect)· B cells that do not become plasma cells turn into memory B cells

memory B cells allows the body to mount an immediate attack when they encounter the same antigen a second time

4 __ cells are responsible for cell-mediated immunity, while __ cells are responsible for humoral immunity.

A T, B

B B, T

C helper T, cytotoxic T

D cytotoxic T, helper T

Primary vs. Secondary Response· primary response - first exposure to a particular antigen

6-7 day lag time after antigen challengeallows B cells for that antigen to replicate and start

producing antibodiespeak levels around 10 days

· secondary response - subsequent exposure(s) to the same antigen

memory cells recognize the antigen

response is faster, longer, and more effective

Antibody Structure· heavy chains - identical to each other; more than 400 amino acids· light chains - identical to each other; half as long as heavy chains· variable region - depends on the antigen· constant region - same for all antibodies· antigen-binding site - variable regions of heavy and light chains; antigen specific

MADGE Antibodies· antibody = immunoglobulin (Ig)· IgM - first antibody released· IgA - found in secretions (i.e. mucus, sweat, etc.)· IgD - found on B cell surfaces· IgG - most abundant antibody; can cross placenta· IgE - involved in inflammation and allergic reactions

The Immune System

5 Immunoglobulins are antigen-specific and are made during the primary response.

True

False

Types of Immunity· specific immunity may involve innate immunity (genetically determined, present at birth) or acquired immunity (developed during life)· 2 types of acquired immunity

active immunity can be naturally acquired (getting sick) or artificially acquired (vaccines)

passive immunity is produced by the natural transfer of antibodies (mom's placenta or milk) or artificial transfer of antibodies (donated antibodies that jumpstart your own attack; hepatitis, snake bites, rabies, tetanus)

6 MATA: When I was sick, I spread my germs every time I coughed. What type(s) of immunity was I helping you develop by sharing my germs? (You're welcome by the way :-))

A acquired

B innate

C specific

D active

E passive

Immune Disorders· immunodeficiencies - immune system does not develop normally or the immune response is blocked

SCID - severe combined immunodeficiency syndromes; very few B and T cells

AIDS - acquired immune deficiency syndrome; results from HIV infection; attacks CD4 proteins/helper T cells· autoimmune diseases - immune response mistakenly targets normal body cells and tissues

multiple sclerosis (MS), Graves' disease, Type 1 diabetes mellitus, lupus, rheumatoid arthritis · hypersensitivities - excessive reactions to harmless threats (allergens)