Innate and Adaptive Immunity

Innate (Natural) Immunity:

Inborn resistance. present the first time a pathogen is

encountered (does not require prior exposure).

Not specific. not modified by repeated exposure to

the pathogen.

Adaptive (Acquired) Immunity:

weak or absent at the first exposure.

Specific. increases dramatically with

subsequent exposures to the same pathogen (memory).

Components of innate immunity:

Cell mediated immunity. Humoral (soluble) immunity.

Types of adaptive immunity

Cell mediated immunity. Humoral (soluble)immunity.

Cells of Innate Immunity: Phagocytes:

- Monocytes and macrophages: blood

stream and tissues.

- Dendritic cells: lung, skin and GIT mucosa.

Granular leukocytes:

- Neutrophils, and eosinophils.

- Basophils and mast cells.

Natural killer cells (NK).

Soluble Mediators of Innate Immunity:

o Proteins and enzymes.

o Cytokines & type 1 interferons.

o Complement (C3b: opsonization).

o Proteins and Enzymes A variety of proteins and enzymes (present in human blood and tissue fluids) are considered the first part of innate immunity. Example: C reactive protein (CRP), lysozymes and defensins.Proteins and enzymes Major microbial targets Effects

Lysozyme and defensins Bacterial wall and membrane

digestion

CRP Polysaccharides of microbes

Opsonization

Mannose binding proteins Mann glycoprotein Opsonizationand complement activation

o Cytokines and Type I Interferons: Cytokines: IL-1, IL-6, IL-12, and TNFα

produced by activated phagocytes.

Type I interferons:

INFs are rapidly produced, within minutes by infected cells (virus infection).

INFs activate phagocytosis and apoptosis of infected cells.

• IFN- α produced by dendritic cells.

• IFN-β Produced by fibroblasts.

Cellular and Humoral Adaptive Immunity:Immune cells:

- T lymphocytes

- B lymphocytes

- N.K cells.

Soluble mediators:

- Cytokines: IL-2, IL-3, IL-10,IL-13.

- Interferons: INF-γ (Gamma).

- Complement.

Soluble and cell-bounded proteins:

-The Immunoglobulins.

n

Phagocytes: monocytes, macrophages & DC

Granular leukocytes

Cytokines: IL1, IL6, IL12 & TNFα.

Interferons: IFα and IFβ.

T lymphocyte & B lymphocytes

Cytokines: IL2, IL3, IL10 & IL13.Interferons: IFγImmunoglobulins.

Complement

NK cell

Antigens, Immunogens , Epitopes and

Haptens

Antigen:

Is a molecule or part of a molecule that is recognized by the immune system.

Immunogen:

Is an antigen that evokes a specific, positive immune response.

Example: Injecting a laboratory animal by human chromosome anti-DNA antibodies and anti-histons antibodies will be produced.

N

Epitopes (The Antigenic determinants): The smallest part of an antigen or immunogen that can be recognized by the B & T cells receptors. So it is the basic recognition element.

A single antigen molecule may have several different epitopes.

Immunodominant epitope is an epitope that can stimulate a greater antibody response than others.

N

epitopes

Immunogenicity and Properties of Immunogen:

Immunogenicity is the ability of immunogen to activate immune response.

Properties of Immunogen:

o Foreignness.

o Size.

o Chemical nature

o Complexity.

Foreignness:

Immune system can discriminate between foreign and self substance (self & non self).

Size:

Molecular weight of at least 10,000 Dalton (10 kDa).

Chemical nature: -Proteins (polypeptide) are good immunogens. -Carbohydrates, steroids, and lipids are poor immunogens.

N

Chemical complexity:

As the chemical complexity increases; the

immunogenicity increases.

Homopolymers are poor immunogens

regardless of size, while heteropolymers are

strong immunogens.

Proteins are heteropolymers (different

amino acids).

N

epitopesWhich of these antigens is more immunogenic?

Epitopes RecognitionB cell receptors can recognize epitopes whether they are:

Free soluble molecules.

Surface-bound molecules.

Degraded fragments.

T cell receptors can bind only to epitopes which are surface-bound molecules.

Superantigen:

o Is a substance such as a bacterial toxin that is capable of stimulating multiple T lymphocytes, leading to release of relatively large quantities of cytokines.

o Phagocytosis process is not required for this type of activation.

N

Hapten:

Small, usually non-biologic molecules that bind to immune cells receptors but cannot by themselves induce a specific immune response.

(Land-Steiner’s experiment).

Injected a mice with:

hapten No immune response

carrier (protein) anti carrier

Hapten + carrier anti-hapten +anti-carrier

T-cell Dependent and T-cell Independent Antigens:

Antigens are classified as either T-cell dependent or T-cell independent.

T cell dependent antigen activates immune system depending on T-lymphocytes.

T-cell dependent antigen

T-cell independent Antigen

Structural properties Complex Simple

Chemical nature Proteins, glycoprotein, and lipoproteins

Polysaccharide; bacterial

Lipopolysaccharide.

Antibody - class induced

IgG, IgM, IgA, IgD, and IgE

Only IgM

Immunological Memory

yes No

Present in most Pathogens

yes No