genetic immunity

• Antibody


  Protein produced by B cells, functions in immune system to identify and neutralize foreign objects such as bacteria and viruses
• Antigen


  Any molecule that can elicit an immune response, typically proteins or carbohydrates
• Antigen may originate from within the body


  "self" or from the external environment "non-self"
• Immune system is usually non-reactive against "self" antigens under normal conditions
• Immune system is supposed to identify and attack only "non-self" invaders
• Major histocompatibility complex (MHC)


  Proteins required to carry out an immune response, coded by a group of genes
• The human MHC is also called the HLA (human leukocyte antigen) complex
• This group of genes is located on the p arm of chromosome 6
• MHC includes > 200 genes
• Genetic influence on immunity stems majorly from MHC genes
• MHC genes

  • Highly polymorphic
  • Diversity plays a very important role in resistance to pathogens
• MHC genes functional groups

  • Class I
  • Class II
  • Class III
• Class III MHC


  Encodes proteins that are in blood plasma, providing nonspecific immune functions
• Class I and II MHC

  Encode proteins that provide specific immune functions
• HLA proteins link to sugar, forming branchlike glycoproteins that extend from cell surfaces
• Some HLA glycoproteins latch onto bacteria and viral proteins, displaying them to alert other immune system cells
• Antigen processing

  First step in an immune response
• Antigen-presenting cell


  The cell that displays the foreign antigen
• T cells or T lymphocytes are also antigen-presenting cells
• A macrophage engulfs a bacterium, then displays foreign antigens on its surface
• Foreign antigens are held in place by MHC proteins
• Basic components of the immune system

  • Humoral response
  • Cellular response
• Physical barriers

  Structures and fluids that keep pathogens from entering the body
• Unbroken skin, mucous membrane, and waving cilia push debris and pathogens out of the respiratory tract
• Most microbes that reach the stomach are killed by gastric acid
• Physical barriers are non-specific
• Innate immunity


  Provides a rapid, broad defense if a pathogen breaches physical barriers
• Inflammation is a central part of the innate immune response
• Inflammation sends in cells that engulf and destroy pathogens
• Plasma accumulates at the infection site, diluting toxins and bringing in antimicrobial chemicals
• Three classes of proteins in innate immunity

  • Complement system
  • Collectins
  • Cytokines
• Mutations/polymorphisms in the genes that encode these proteins modify susceptibility to infection
• Certain polymorphisms in CR1 can confer protection from severe malaria
• Certain polymorphisms in IL10 can increase the risk of Kawasaki disease
• Certain polymorphisms in MBL2 can increase the risk of asthma
• Adaptive immunity


  May take days to respond, compared to minutes for innate immunity
• Adaptive immunity is highly specific and directed, involving B cells and T cells
• B cells produce antibodies in response to activation by T cells
• T cells produce cytokines and activate other cells
• B and T cells differentiate in the bone marrow and migrate to lymph nodes, spleen, thymus gland, bloodstream, and tissue fluid