Define antigens, what types elicit the strongest immune response

• Antigens refer to foreign molecules that provoke a response by the immune system

• Most antigens are proteins produced by bacteria or viruses

  • Specifically glycoproteins which are carbohydrate residues and lipoproteins

    • Lipid residues are highly antigens with a very strong immune response

• Strongest to weakest immune response

  • Proteins

  • Polysaccharides

  • Lipids

  • DNA

Basic role of antibody in the immune response

• Immune system molecules recognize and bind to antigens

• B cells can generate billions of different antibodies

• B cells recognize antigens and make antibodies

  • They then divide rapidly and go into mass production

• Antigens determines which antibody is produced and amplified

• Some antibody clones are mutated or refined to be more specific

• Antibodies generally bind to the whole protein

  • They recognize a small surface area (recognition sites are called epitopes) of the antigen

Diagram structure of antibody

• 2 light and 2 heavy chains

• Chains use disulfide bonds between cysteine amino acid residues

• Each light/heavy chain has constant or variable regions

  • Constant regions are the same for same class chains

  • Variable region binds to the target antigen

  • Hinge is where the heavy chain bends

  • The heavy chain is one Fc fragment, and is crystallizable

  • The light chain has two Fab fragments which are antigen binding

• Diagram

How does antibody diversity arise?

• Vast numbers of foreign particles requires a vast number of antibodies

• The immune system generates different protein sequences by shuffling a small number of genes via their segments

• Complete genes for each antibody are not stored

  • Instead, the antibody genes are assembled from shorter gene segments

  • Shuffling and joining partial genes allows for a variety of antibodies

• example: 10 front, 10 middle, and 10 end segments can give rise to 1000 variants

  • this requires only storing 30 DNA coding segments

• In mammals, 95% of DNA is noncoding but billions of antibodies from only 1000s of gene segments

Outline humoral and cell mediated immunity

• Basically, specific immunity vs acquired immunity

  • Acquired is subdivided into humoral and cell mediated immunity

• Humoral immunity is mediated by antibodies (immunoglobulins) in blood plasma produced by B-cells

• Cell mediated immunity is mediated by antigen specific cells (ie, T lymphocytes)

  • T lymphocytes divided into Th (helper) and Tc (cytotoxic)

• T cell receptors bind to protein fragments

  • When the antibody binds to proteins, it recognizes a small area on the protein surface (dimples or projections)

  • Recognition sites are called epitopes

  • Intact proteins are large molecules and may have several epitopes

• T cells recognize antigens expressed on the surface of other body cells