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Immune System

A host defense system comprising many biological structures and processes within an organism that protects against disease.


To funciton properly, what must the immune system do?

To function properly, an immune system must detect and destroy a wide variety of agents, known as pathogens, from bacteria to viruses to parasitic worms, and distinguish them from the organism's own healthy tissue.


What are the subsystems of the immune system?

  • Innate Immune System
  • Adaptive/Acquired/Specific Immune System



What are the characteristics of the innate immune system?

  • Response is non-specific
  • Exposure leads to immediate meximal response
  • No immunological Memory
  • Found in nearly all forms of life



What are the characteristics of the adaptive immune system?

  • Pathogen and antigen specific response
  • Lag time between exposure and maximal response
  • Exposure leads to immunological memory
  • Found only in jawed vertebrates



Inna (non-specific) Immunity

General response with no memory; first, inflammatory response brings blood and "fighter" cells to infection.



Part of the innate response that can eat up pathogen; use cell receptors to "identify" foreign or dead/unusable material.



Organelles that fuse with pathogen vesicle, digest inner material (pathogen) with lysozymes (digestive enzymes).


What heppens to the pieces digested by lysosomes (in phagocytes)?

Pieces of degraded material (say, a piece of a viral protein) will then be attached to an MHC Type II protein and it will be presented on the surface of the cell.


What type of cell are phagocytes when related between the two subsystems?

Phagocyte is thus an "antigen presenting cell". Now, specific or acquired immune system can do its thing.


What are the types of phagocytes?

  • Neutrophils (most abundant; fast responders)
  • Macrophages (do much of the heavy lifting)
  • Dendritic Cells (nothing to do with nervous system; look like they have dendrites - best activators of acquired immune system).

All are considered white blood cells or leukocytes.


Which subsystem arose first?

Specific/adaptive/acquired immune system is though to have arison more recently, while the innate immune system was thought of as arising earlier in evolution. 


Who are the main players of acquired immune system?

Main players are lymphocytes (also considered a WBC/leukocyte like phagocytes). These are divided into B cells and T cells.


Where do the lymphocytes originate from?

B cells produced in bone marrow, while T cells are born in bone marrow but mature in thymus. (Remember, RBCs carries oxygen, WBCs are everything else)


In which reponse do B and T cells participate?

B lymphocytes participate in the humoral response. T cells participate in cell-mediated response. Helper T cells and Cytotoxic T cells both carry out this cell-mediated response.


Where does the humoral response (and cell-mediated) act?

Humoral Response deals with pathogens outside of the cells. Once, inside, cell-mediated.


Humoral Response

B cells have antibodies on their surface that can recognize "antigens". Each cell has a different antibody on its surface. With variable portions approximately 1011 or 1012 combinations. 


How does the variation in the antibody occur?

DNA rearrangment of exons (including variable regions; like differential splcing) This occurs during development of the B cells (once they are born, recombination events occur).



The part that is recognized by antibody; self-responding combinations are weeded out so they do not cause damage to own body. 


What happens when antibody binds a pathogen?

After antibody binding to pathogen, B cell becomes activated (need help form helper T cells for this to happen). Now, the B cell will proliferate (amplify its population). 


What cells results form the proliferation of the B cells?

Some amplified cells will become memory cells for future exposures to pathogen, others will become effector (plasma) cells.


What is the role of effector cells?

Effector cells become antibody factories that get secreted. Now, these antibodies can bind to pathogen (say, virus) in the fluid around the cells (humoral response). Targets viruses for attach by phagocytes.


Besides producing antibodies, what else can B cells do?

B cells (like phagocytes) can also present anitgens on surface; helper T cell can recognize antigen complex and then becomes activated (proliferate). 


What results from the proliferation of the helper T cells?

Third class of lymphocyte becomes either effector or memory T cell, also aided by helper T cells.