733 Immune System

innate immunity

non-specific immunity because it protects the body from any agent that may cause injury to cells

components to innate/non-specific immunity

• barrier defenses (physical barriers)

• inflammatory response (cellular response)

function of barrier defenses

• prevent the entrance of microorganisms into the body

• destroy pathogens that enter

• flush pathogens out of the body

skin speficic defense

epidermal surface

skin protective aspect

keratinized cells of surface, langerhans cells

skin (sweat/secretions) specific defense

sweat glands, sebaceous glands

skin (sweating/secretions) protective aspect

low pH, washing action

oral cavity specific defense

salivary glands

oral cavity protective aspect

Lysozyme

stomach specific defense

gastrointestinal tract

stomach protective aspect

low pH

mucosal surfaces specific defense

mucosal epithelium

normal flora (nonpathogenic bacteria) specific defense

mucosal tissue

normal flora (nonpathogenic bacteria) protective aspect

prevent pathogens from growing on mucosal surfaces

inflammatory response

a nonspecific response to any agent that causes cell injury

dendritic cells

specialized immune cells that act as the master bridge between the body’s innate and adaptive immune systems

agents that cause cell injury may be

• physical

• chemical

• microbiologic/pathogens

tissue injury causing capillary widening leads to

increased blood flow

tissue injury causing increased permeability leads to

fluid release into tissues

tissue injury causing attraction of leukocytes leads to

extravasation of leukocytes to site of injury

tissue injury systemic response leads to

fever and proliferation of leukocytes (rapid WBC division)

cells involved in inflammation

neutrophils, monocytes, macrophages, mast cells, basophils, eosinophils, lymphocytes

neutrophils and monocytes

leukocytes that digest harmful substances

cells that release chemical mediators of inflammation

basophils, platelets, injured tissue cells

basophils

a leukocyte and source of histamine (a vasodilator) and when they migrate into tissue they are called mast cells

platelets

play an important role in blood clotting

chemical mediators of inflammation

compounds that are formed and released when tissue is damaged. Some are derived from cells and other are derived from proteins in blood plasma

cell derived chemical mediators of inflammation

histamine, leukotrines, prostoglandins, cytokines

histamine

a potent vasodilator

leukotrines

attract leukocytes to site of injury

prostoglandins

vasodilator and sources of pain in inflammation

cytokines

regulate the direction/movement of leukocytes

plasma derived chemical mediators of inflammation

bradykinins, complement

bradykinins

a vasodilator and source of pain in inflammation

complement

a group of proteins that attacks foreign substances

phagocytic response pathway

1. blood vessels dilate bringing increased blood flow to the injured area

2. phagocytes migrate to the injury site and ingest microbes and other foreign substances

3. lymphatic drainage removes dissolved poisonous substances for healing to occur

phagocytic reponse

neutrophils and monocytes (macrophages) are the primary phagocytes in the body. They contain lysosomes which are vesicles with strong digestive enzymes that destroy microbes

appendicitis

infected/inflamed appendix

hepatitis

infected/inflamed liver

colitis

infected/inflamed colon

cellulitis

an acute spreading infection of the skin or deeper tissues

sepsis

occurs when an infection spreads throughout the bloodstream and body, leading to widespread inflammation . This is a life-threatening condition that must be treated immediately

septic joint or septic arthritis

occurs when an infection spreads to a joint which causes localized joint inflammation. Without treatment can cause degeneration of articular cartilage

outcomes of infection

1. recovery

2. chronic infection

3. death

adaptive specific immunity

ability of the body to defend itself against specific invading agents such as bacteria, toxins, viruses, and foreign tissues

2 main properties of adaptive (specific) immunity

1. specificity→for particular foreign antigens

2. memory→ for most previously encountered antigens

antigen

foreign substances that provoke immune response with two characteristics: immunogenicity and reactivity

immunogenicity

the ability to provoke an immune response

reactivity

ability of an antigen to react specifically with the cells or antibodies it provoked

epitope

the portion of antigen that triggers a reaction

lymphocytes of the immune system

T cells and B cells (and natural killer cells not specific)

what happens at T cells and B cells mature

they become immunocompetent (prepared to carry out immune response) and make a receptor for specific antigens

cytotoxic T cells (T8 cells) function

• effectors of cell-mediated immunity

• contain CD8 protein on plasma membrane

B cells function

• secrete antibodies

• effectors of humoral immunity

helper T cells (T4 cells) function

• regulate function of B cells and cytotoxic T cells

• contain CD4 protein on plasma membrane

peptide (protein messengers)

what immune cells secrete to communicate with each other

cytokine

general term for a chemical messenger that takes part in immune response

lymphokines

chemicals from lymphocytes

monokines

chemicals for monocytes

interferons

interfere with viral replication

interluekins

send regulatory signals

tumor necrosis factors (TNF)

destroy tumor cells

what happens when foreign antigens enter the body

1. Antigen processing and presenting

2. activation of T and B cells

3. Destroy foreign antigens and infected cells

4. Memory cells remain in the body

antigen and immune response

slow process, can take a week between arrival of antigen and immune response

(1)antigen processing and presenting

to get the immune system started, the antigen must be processed. This occurs within infected body cells and when phagocytes engulf the antigen. The antigen is broken down, combined with a specialized protein, and inserted into the cell membrane

where does antigen processing occur

1. inside infected body cells

   1. within phagocytic cells (APCs) which are neutrophils and macrophages apart of the non specific immune response and dendritic cells

what does antigen combine with

combines with major histocompatibility complex (MHC) which are then inserted onto the plasma membrane

major histocompatibility complex (MHC) proteins

special proteins on the plasma membrane that designate cells as “self” and serve as a carrier for processed foreign antigens

MHC I

present on all body cells, except RBC

MHC II

appear only on antigen-presenting cells that are a carrier for foreign antigens that are outside cells

(2)activation of T and B cells

needs 2 things to occur

1. recognition

2. co-stimulation

activation of T and B cells → recognition

T cells (cytotoxic and helper) recognize only processed antigen combined with MHC complexes

B cells recognize both the processes and unprocessed antigen

activation of T and B cells → co-stimulation

cytokines released from helper T cells provide the necessary stimulation

(3) destroy foreign antigens and infected cells 2 pathways

1. cell mediated immunology → T8 cells

2. humoral immunity → B cells secreting antibodies

cell mediated immunology

once activated, cytotoxic T cells multiply then, they travel through the body to destroy infected cells

humoral (antibody-mediated) immunity

activated B cells are called plasma cells. Plasma cells stay in lymph and multiply. Plasma cells release antibodies to destroy invaders with antibodies on the B cell receptor

immunoglobins

plasma protein with antigen binding site and is variable and specific to an antigen

IgG

antibodies that are most prevalent during secondary immune reponses

IgA

found in bloodstream, mucous membranes; contained in breast milk

IgM

first to respond in primary immune response. Very large and effective at combining with antigens

IgE

attaches to mast cells and basophils; mediates allergic reactions

actions of antibodies

• neutralize antigen

• immobilize bacteria

• agglutinate and precipitate antigen for easier digestion by macrophages

• enhance phagocytosis

• activate complement system

complement system

set of proteins activated by antigen-antibody interaction

(4) memory cells remain in body

memory cells that survive after an initial exposure (the primary response) to a specific antigen lead to a much faster secondary response if the same antigen is encountered again

immune system in infancy and childhood

babies are born with an intact innate immune system and adaptive immunity develops throughout childhood from exposure. there is some initial protection from the mother’s immune system (IgG in pregnancy and IgA in breastmilk)

advanced age

associated with a decline in the immune system potentially caused by age relate atrophy of the thymus

exercise and the immune system

a J shaped relationship between risk of infection and exercise intensity. The immune system is strengthened following bouts of moderate exercise and is weakened following high intensity volume of exercise

hypersensitivity

an abnormal immune response that can lead to tissue damage occurs in two stages: sensitization stage and effector phase

sensitization phase

initial encounter with an antigen

effector phase

immunological memory that triggers an abnormal response

Type I hypersensitivity

immediate hypersensitivity

Type II hypersensitivity

cytotoxic hypersensitivity

Type III

immune complex hypersensitivity

Type IV hypersensitivity

delayed hypersensitivity (cell-mediated)

Type I: Immediate Hypersensitivity

(AKA allergy or anaphylaxis) immediate hypersensitivity reactions occur when a person encounters specific allergens that trigger an immune response and the formation of IgE antibodies

Type I: Immediate Hypersensitivity first exposure

to allergen (sensitization) plasma cells secrete IgE antibodies which attach to mast cells and basophils and is usually asymptomiatic

Type I; Immediate Hypersensitivity subsequent exposures

IgE-allergen interaction causes mast cells and basophils to release histamine and prostaglandins which leads to an allergic reaction

allergy

localized response of tissues exposed to allergen

allergy treatment

• antihistamines

• desensitize with subcutaneous injections → IgA and IgG antibodies react with it before IgE

anaphlaxis

widespread, systemic reaction to allergen with symptoms including increased vasodilation leading to decreased blood pressure and constriction of airways leading to respiratory distress. Requires immediate treatment with epinephrine