The Immune SystemThe Immune System

Dr. Jena Hamra

Immune SystemImmune System

3 major functions Protects body from disease

Bacteria, viruses, fungi, parasites ANTIGEN: Anything that causes immune response

Remove dead or damaged tissue Recognizes and removes abnormal cells

2 types of immune responses Innate immunity

Nonspecific, immediate Acquired immunity

Specific, can take several days

Anatomy of the Immune SystemAnatomy of the Immune System

Lymphoid tissuesPrimary

Bone marrowThymus gland

SecondarySpleenLymph nodesDiffuse tissues

• Tonsils• GALT

Cells of the Immune SystemCells of the Immune System

LeukocytesEosinophilsBasophils/Mast cellsNeutrophilsMonocytes/MacrophagesLymphocytesDendritic cells

Cell FunctionCell FunctionGRANULOCYTESEosinophils

Fight parasitesAllergic reactions

BasophilsRelease histamine, heparin

NeutrophilsIngest and digest bacteriaMost abundant WBC in bloodRelease pyrogens, mediators of inflammation

Cell FunctionCell Function Lymphocytes

Secrete antibodies Memory cells Cytotoxic cells

Monocytes Macrophages in tissue Primary scavengers

Bacteria, tissue Antigen presenting cells

Dendritic cells Recognize, capture antigen Antigen presenting cells

Innate ImmunityInnate Immunity

Nonspecific responsePhysical barriers

SkinMucous membranesCiliated epithelium

PhagocytesMacrophages and neutrophilsPhagocytosis

Receptor mediatedExtravasation and diapedesis

Chemical MediatorsChemical Mediators

InflammationCytokines from macrophages

ChemotaxisIncrease capillary permeabilityFever

Acute phase proteinsProduced by liverReleased early in immune responseOpsonins, antiprotease

Chemical MediatorsChemical Mediators Histamine

Located in granules of mast cells and basophils Initiates inflammatory response

Increase capillary permeability• Edema

Vasodilation• Increased local blood flow

Interleukins Interleukin-1

Secreted by activated macrophages Increase capillary permeability Stimulates acute phase protein synthesis Induces fever Stimulates cytokine release

Chemical MediatorsChemical Mediators

BradykininVasodilatorStimulates pain receptors

Complement proteinsCascadeFormation of membrane attack complex

Lipid soluble moleculesInsert into pathogen membrane, form pores

• Cell lysis

Acquired ImmunityAcquired Immunity

Selective reaction to a specific antigenMediated by lymphocytes

Membrane receptors specific for particular ligand

Same specificity = clonesClonal expansion

First exposure to antigenCells divide = new clonesProduces effector cells and memory cells

Second exposure to antigenActivation of memory cells

Lymphocyte CytokinesLymphocyte Cytokines

Required for activation and normal immune response

InterleukinsClonal expansion and differentiation

InterferonsAlpha and beta: activate pathways against viral

infectionGamma: Activates macrophages

Lymphocyte SubtypesLymphocyte Subtypes

B lymphocytesSecrete antibodies

T lymphocytesHelper T cells (CD4): Secrete cytokines

required for development of immune responseCytotoxic T cells (CD8): Attack and destroy

foreign cellsNatural killer cells: Attack and destroy virally

infected or cancer cells

Antibody Secretion Antibody Secretion (Humoral Immunity(Humoral Immunity

B cellsActivated B cells Plasma cells

Plasma cells secrete antibodiesPrimary and secondary antibody response

Primary: Slower and and weakerIgM

Secondary: Faster, more antibodies producedIgG

AntibodiesAntibodies

IgG 75%, Secondary response

IgM Primary antibody response

IgA Secretory: saliva, tears

IgE Allergic responses

IgD Cell surface receptor on B lymphocytes

Antibody StructureAntibody StructureY shaped proteins

2 heavy chains, 2 light chainsFab region: antigen binding sites

Antibody FunctionAntibody Function

Opsonins Coat antigens, facilitate phagocytosis

Make antigens clump Activate other immune cells

Cytotoxic T cells Phagocytic cells B lymphocytes

Activate complement Activate mast cells

Cellular ImmunityCellular Immunity T lymphocytes

Mature in thymus Require antigen presenting cells Cytotoxic T cells Helper T cells

T cell receptor Required for recognition of antigen

Major histocompatibility complexes Required for antigen presentation CD4 recognize MHC II CD8 recognize MHC I