Antibodies And hypersensitivity, Slides of Microbiology

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ANTIBODY- STRUCTURE,

CLASSES AND FUNCTIONS

DEFINITION OF ANTIGEN & ANTIBODY

Antigens :

are molecules capable of stimulating an immune response.

Each antigen has distinct surface features, or epitopes, resulting in

specific responses.

Antibodies

(immunoglobins) are Y-shaped proteins produced by B cells of the

immune system in response to exposure to antigens.

STRUCTURE OF ANTIBODY There are four polypeptide chains: two identical heavy chains and two identical light chains connected by disulfide bonds. Light Chain (L) consists polypeptides of about 22,000 Da and Heavy Chain (H) consists larger polypeptides of around 50,000 Da or more. There are five types of Ig heavy chain (in mammal) denoted by the Greek letters: α, δ, ε, γ, and μ. There are two types of Ig light chain (in mammal), which are called lambda (λ) and kappa (κ).) and kappa (κ).). An antibody is made up of a variable region and a constant region, and the region that changes to various structures depending on differences in antigens is called the variable region , and the region that has a constant structure is called the constant region.

Each heavy and light chain in an immunoglobulin molecule contains an amino-terminal variable (V) region that consists of 100 to 110 amino acids and differ from one antibody to another. The remainder of each chain in the molecule – the constant (C) region exhibits limited variation that defines the two light chain subtypes and the five heavy chains subclasses. Some heavy chains (α, δ, γ) also contain a proline-rich hinge region. The amino terminal portions, corresponding to the V regions, bind to antigen; effector functions are mediated by the carboxy-terminal domains. The ε and μ heavy chains, which lack a hinge region, contain an additional domain in the middle of the molecule. CHO denotes a carbohydrate group linked to the heavy chain.

FUNCTIONS OF ANTIBODY IgG provides long term protection because it persists for months and years after the presence of the antigen that has triggered their production. IgG protect against bacteria, viruses, neutralize bacterial toxins, trigger compliment protein systems and bind antigens to enhance the effectiveness of phagocytosis. Main function of IgA is to bind antigens on microbes before they invade tissues. It aggregates the antigens and keeps them in the secretions so when the secretion is expelled, so is the antigen. IgA are also first defense for mucosal surfaces such as the intestines, nose, and lungs. IgM is involved in the ABO blood group antigens on the surface of RBCs. IgM enhance ingestions of cells by phagocytosis. IgE bind to mast cells and basophils wich participate in the immune response. Some scientists think that IgE’s purpose is to stop parasites. IgD is present on the surface of B cells and plays a role in the induction of antibody production.

Hypersensitivity -Exaggerated immune response that causes damage to the individual. Immediate hypersensitivity (types I, II, and III) is mediated by antibody or immune complexes, and delayed-type hypersensitivity (type IV) is mediated by TH cells.

• Primary mediator is the adaptive immune system T & B lymphocytes
• Damage is mediated by the same attack mechanisms that mediate normal immune responses to pathogen. Young girl sneezing in response to flowers. [Brand New Images/Getty Images] Allergy: A type I hypersensitive reaction

• Two French scientists, Paul Portier and Charles Richet, were the first to recognize and describe hypersensitivities for which Richet was subsequently awarded the Nobel Prize in Physiology or Medicine in 1913.
• As part of their studies to the stings of Physalia physalis, they demonstrated that the toxic agent in the sting was a small protein. They reasoned that eliciting an antibody response that could neutralize the toxin may serve to protect the host. Paul Portier Charles Richet

MULTIPLE TYPES OF HYPERSENSITIVITY REACTIONS

• (^) Immediate hypersensitivity reactions result in symptoms that manifest themselves within very short time periods after the immune stimulus resulting from antibody-antigen reactions.
• (^) Hypersensitivity reactions that take hours or days to manifest themselves are referred to as delayed- type hypersensitivity (DTH) reactions resulting from T-cell reactions.

• (^) Type I
• (^) Type II
• (^) Type III
• (^) Type IV Type I, II and III Type IV Antibody Mediated Cell Mediated 7 CLASSIFICATION OF HYPERSENSITIVITY

• (^) Type III hypersensitivity reactions , antigen- antibody complexes deposited on host cells induce complement fixation and an ensuing inflammatory response.
• (^) Type lV hypersensitivity reactions result from inappropriate T-cell activation.

 (^) Commonly called allergy  (^) In type 1 hypersensitivity, B-cells are stimulated (by CD4+TH2 cells) to produce IgE antibodies specific to an antigen. The difference between a normal infectious immune response and a type 1 hypersensitivity response is that here the antibody is IgE instead of IgA, IgG, or IgM.  (^) The antigens that stimulate it are called allergens (i.e. House dust, Pollens, Cosmetics, Insects, Clothing and Drug)  (^) Exposure may be through ingestion, inhalation, injection or direct contact.  (^) Type I hypersensitivity reactions can be systemic (e.g., systemic anaphylaxis) or localized to a specific target tissue or organ (e.g., allergic rhinitis, asthma). TYPE I (IMMEDIATE) HYPERSENSITIVITY

 (^) Type III hypersensitivity is also known as immune complex hypersensitivity.  (^) The reaction may take 3 - 10 hours after exposure to the antigen (as in Arthus reaction).  (^) The reaction may be general ( e.g. , serum sickness) or may involve individual organs.  (^) Antigens causing immune complex mediated injury are:  (^) Exogenous  (^) Endogenous TYPE III (ICM- IMMUNE COMPLEX– MEDIATED) HYPERSENSITIVITY

IMMUNE COMPLEX DISEASES-  Hypersensitivity Pneumonitis- Hypersensitivity pneumonitis is an inflammation of the alveoli within the lung caused by hypersensitivity t o inhaled organic dusts. Sufferers are commonly exposed t o the dust by their occupation or hobbies.  Glomerulonephritis- Glomerulonephritis (GN) is inflammation of the glomeruli, which are structures in your kidneys t h a t are made up of tiny blood vessels. These knots of vessels help filter your blood and remove excess fluids. If glomeruli are damaged, kidneys will stop working properly and one can go into kidney failure.