IMMUNOLOGY

Immunology A branch of biomedical science that covers the study of all aspects of the immune system in all organisms. It deals with the functioning of the immune system in states of both health and diseaseAlso adresses malfunctions of the immune system in immunological disorders (autoimmune diseases, hypersensitivities, immune deficiency, transplant rejection)

ImmunityDescribes a state of having sufficient biological defences to avoid infection, disease, or other unwanted biological invasion. Involves both specific and non-specific components. The non-specific components act either as barriers or as eliminators of wide range of pathogens irrespective of antigenic specificity.Specific components adapt themselves to each new disease encountered and are able to generate pathogen-specific immunity

Three Lines of Defense Against Infection

PHAGOCYTOSIS

Derived from the Greek words Eat and cell. Phagocytosis is carried out by white blood cells: macrophages, neutrophils, and occasionally eosinophils.Neutrophils predominate early in infection.Wandering macrophages: Originate from monocytes that leave blood and enter infected tissue, and develop into phagocytic cells.Fixed Macrophages (Histiocytes): Located in liver, nervous system, lungs, lymph nodes, bone marrow, and several other tissues.

Phagocytic Cells: Macrophages (Monocytes), Neutrophils, and Eosinophils(Macrophages)

Stages of Phagocytosis

1. Chemotaxis: Phagocytes are chemically attracted to site of infection.2. Adherence: Phagocyte plasma membrane attaches to surface of pathogen or foreign material. Adherence can be inhibited by capsules (S. pneumoniae) or M protein (S. pyogenes). Opsonization: Coating process with opsonins that facilitates attachment. Opsonins include antibodies and complement proteins.

Phagocytes are Attracted to Site of Infection by Chemotaxis

Stages of Phagocytosis (Continued) 3. Ingestion: Plasma membrane of phagocytes extends projections (pseudopods) which engulf the microbe. Microbe is enclosed in a sac called phagosome.4. Digestion: Inside the cell, phagosome fuses with lysosome to form a phagolysosome. Lysosomal enzymes kill most bacteria within 30 minutes and include:Lysozyme: Destroys cell wall peptidoglycanLipases and ProteasesRNAses and DNAsesAfter digestion, residual body with undigestable material is discharged.

Process of Phagocytosis

Phagocytes as Antigen-Presenting CellsTakes place after phagocytosis

Antigen presentation : - Phagocyte moves parts of the ingested material back to its surface. - This material is then displayed to other cells of the immune system. - Some phagocytes then travel to the body's lymph nodes and display the material to white blood cells called lymphocytes.

Important in building immunity. However, many pathogens have evolved methods to evade attacks by phagocytes

Mast cellsAlso known as mastocytes and labrocytes

A resident cell of several types of tissues and contains many granules rich in histamine and heparin.

Best known for their role in allergic reactions (eg. Eczema) and anaphylaxis (a severe systemic reaction to allergens, such as nuts, bee stings or drugs)

Also play an important protective role because they are intimately involved in wound healing and defense against pathogens

Mast cells continuedConnective tissue cells Normal function is unknown

Frequently injured in allergic reactions, releasing chemicals including histamine that are very irritating and cause itching, swelling, and fluid leakage from cells. These allergic chemicals may also cause muscle spasm and lead to lung and throat tightening, as in asthma

HistamineAn organic nitrogen compound involved in local immune responses Produced by basophils and mast cells found in nearby connective tissues. Increases the permeability of the capillaries to white blood cells and some proteins, in order to allow them to engage foreign invaders in the infected tissues.Found in virtually all animal body cells.

Complement System Large group of serum proteins that participate in the lysis of foreign cells, inflammation, and phagocytosis.Two mechanisms of complement activation:1. Classical Pathway: Initiated by an immune reaction of antibodies.2. Alternative Pathway: Initiated by direct interaction of complement proteins with microbial polysaccharides.

Consequences of Complement Activation: 1. Cytolysis: Due to the formation of a membrane attack complex (MAC) which produces lesions in microbial membranes.2. Inflammation: Complement components trigger the release of histamine, which increases vascular permeability.3. Opsonization: Complement components bind to microbial surface and promote phagocytosis.4. Inactivation of Complement: Regulatory proteins limit damage to host cells that may be caused by complement.

Home WorkRead with the following in mind: - Define the term immune response - Compare the origin and maturation of B- and T- lymphocytes-Read up on the humoral and cell-mediated immune responses

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