Host response

• Immunology


  The study of the immune system and the immune response
• Properties that make an antigen immunogenic


  • Foreignness and genetic composition
  • Chemical composition and complexity
  • Molecular size and stability
  • Mode of entry of the antigen
• Bovine Serum Albumin (BSA)


  • Protein which is not immunogenic
• The more foreign the antigen is, the more is its immunogenicity
• Antigens can be chemically classified as

  • Relatively complex polysaccharide
  • Associated with protein carriers
  • Not immunogenic by themselves but become immunogenic if conjugated to protein carriers
• Greater the molecular weight, the more is the immunogenicity
• According to FDA


  In general, intradermal, subcutaneous, and intramuscular routes of administration are associated with increased immunogenicity compared to intravenous routes
• The immune system


  • Composed of molecular and cellular components derived from the lymphoid organs
  • The central lymphoid organs are the primary sites for differentiation and maturation of the cells
• The central lymphoid organs

  • Lymph nodes
  • Spleen
  • Mucosa-associated lymphoid tissues (MALT)
• White Blood Cells (WBC)

  • Granulocytes (e.g. Neutrophil): 50% - 80% of WBC
  • Lymphocytes: 20 - 45% of WBC
  • Monocytes and Macrophages: 3% - 8% of WBC
• Role of different WBC

  • Neutrophils play a major role in acute inflammation and bacterial infections
  • B cells, macrophages and dendritic cells are the professional antigen presenting cells
  • Lymphocytes and macrophages are mainly involved in chronic inflammation
  • Lymphocytes are the predominant inflammatory cells in viral infections
  • Macrophages are predominant in chronic inflammation
• Eosinophils


  • Possess eosinophilic granules that play an important role in type I hypersensitivity reaction or allergy
  • Role in producing basic protein which is toxic to parasites (e.g. Helminths or worms)
• Origin of the cells of the immune system

  1. Multipotent hematopoietic stem cell (hemocytoblast)

  2. Myeloid stem cell

  3. Lymphoid stem cell

  4. Differentiation into various cell types
• White blood cells that play an important role in the body's immune responses

  • Granulocytes
  • Agranulocytes
  • Neutrophil
  • Eosinophil
  • Basophil
  • Monocyte
  • Lymphocyte
• B Cells and T Cells

  • Most important cells of the immune system
  • Involved in adaptive immunity
• Maturation of B cells and T cells

  1. Plasma cells (antibody producing)

  2. Memory B Cells

  3. Helper T cells

  4. Regulatory T cells

  5. Cytotoxic T cells
• Innate Immunity


  Known as natural immunity, the immunity is non-specific
• First Line of Defense

  1. Physical and chemical barriers prevent attachment and entry of the organisms

  2. Normal flora of the skin form a biological barrier
• Second Line of Defense

  1. Inflammation is activated as well as the natural killer cells

  2. Recognized by innate immune cells and soluble mediators due to their molecular patterns called pathogen-associated molecular patterns

  3. Inflammatory cells possess pattern recognition receptors which allow them to act on these pathogenic microorganisms
• Important components of innate immunity

  • Neutrophils
  • Macrophages
  • Interferons
  • Complement System
  • Inflammatory response
• Adaptive Immunity


  1. Involves the T cells and B cells

  2. Microbes able to escape the second line of defense are acted upon by the final line of defense which is the immune response
• First line of defense

  Microorganisms that penetrate it are prevented from multiplying inside the body by the second line of defense
• Second line of defense

  Inflammation is activated as well as the natural killer cells
• Innate immune cells and soluble mediators

  Recognize microorganisms due to their molecular patterns called pathogen-associated molecular patterns (PAMPs)
• Inflammatory cells


  Possess pattern recognition receptors which allow them to act on these pathogenic microorganisms
• Factors that limit the entry of microorganisms

  • Mode of action
• Factors that limit growth of the microorganisms


  • Mode of action within the body
• Neutrophils


  • Ingest and destroy microbes
• Macrophages


  • Ingest and destroy microbes; presents antigens to T cells
• Interferons


  • Inhibit viral replication; produce anti-viral state
• Complement System


  • Membrane attack complex creates holes in bacterial cell membrane; components activate inflammation
• Inflammatory response


  • Limits spread of microbes by destroying them
• Adaptive immunity


  Specific acquired response to an antigen that is initiated by recognition of specific epitopes of the foreign invaders; possesses memory
• Types of immunity


  • Active
  • Passive
• Antibodies


  Globulin proteins (immunoglobulins) that react specifically with the antigens that stimulate their production
• Functions of antibodies


  • Neutralize toxins and viruses
  • Opsonize microbes so they are readily recognized and more easily phagocytosed
  • Activate complement system
  • Prevent attachment of microbes to mucosal surfaces
• Antigen binding


  Fab, Biological mediation, Interchain disulfide bonds, Intrachain disulfide bonds
• Antibody classes


  • IgG
  • IgM
  • IgA
  • IgE
  • IgD
• Complement system


  Consists of a group of soluble proteins (C1 to C9) which are proteases that cleave and activate one another in a sequential manner
• Complement system pathways


  • Classical pathway
  • Alternative pathway (properdin pathway)
  • Mannose binding lectin or MBL pathway