pathogen

Examples of pathogen in the following topics:

• WBC Function

  • The innate immune system is non-specific and refers to the general ability of the body to prevent pathogen entry and destroy pathogens that do enter the body.
  • Phagocytosis of pathogens.
  • It involves the binding of an Fc receptor to a tail on a pathogen, engulfing the pathogen, and using enzymes and free radicals inside the leukocyte to destroy the pathogens.
  • When pathogens are encountered, granule dependent apoptosis (a mechanism of cytotoxicity) may be induced in the pathogen by releasing perforins, granzymes, and proteaseases from their granules.
  • The adaptive immune system is specific to each pathogen on the basis of antigens, which are molecular components of pathogens that are used by leukocytes to recognize that specific pathogen.

• Types of Adaptive Immunity

  • T-cells will then circulate through the body to destroy pathogens in several ways.
  • Helper-T cells facilitate the immune response by guiding cytotoxic T-cells to pathogens or pathogen-infected cells, while the cytotoxic T-cells will kill the pathogens or pathogen-infected cells.
  • Some of the ways in which cytotoxic T-cells kill pathogens include the release of granules that contain the cytotoxins perforin and granzyme, which lyse small pores in the membrane of a pathogen.
  • The overall functions of antibodies are to bind to pathogens to opsonize them, which makes it easier for phagocytic cells to bind and destroy the pathogen.
  • They can also neutralize the toxins produced by certain pathogens.

• Overview of Adaptive Immunity

  • This mechanism allows the immune system to mount stronger attacks each time the pathogen is encountered, thus preparing itself for future challenges and preventing reinfection by the same pathogen in the future.
  • The generation of responses that are tailored to maximally eliminate specific pathogens or pathogen-infected cells
  • The development of immunological memory, where each pathogen is "remembered" by a signature antibody , which can then be called upon to quickly eliminate a pathogen should subsequent infections occur
  • An antigen is any molecule that induces an immune response, such as a toxin or molecular component of a pathogen cell membrane, and is unique to each species of pathogen.
  • Pathogens that undergo mutation will often have different antigens than the ones known by memory B and T cells, meaning that different strains of the same pathogen will still be able to avoid the memory enhanced immune response.

• Immunological Memory

  • These memory cells will remember all specific pathogens encountered during the animal's lifetime and can thus call forth a stronger response, called the secondary immune response, if the pathogen ever invades the body again.
  • Newborn infants are particularly vulnerable to infections since they have no prior exposure to pathogens.
  • During a vaccination, the antigen of a pathogen is introduced into the body and stimulates the immune system to develop a specific immunity against that pathogen.
  • It doesn't cause the disease that the pathogen brings because the vaccine uses an "attenuated", or weakened form of the pathogen that contains the same antigen but doesn't have the capacity for replication.
  • These memory cells will remember all specific pathogens encountered during the animal's lifetime and can thus call forth a strong response if the pathogen ever invades the body again.

• Structure and Function of Antibodies

  • An antibody (formally called immunoglobulin) is a large Y-shaped glycoprotein produced by B-cells and used by the immune system to identify and neutralize pathogens.
  • Eliminates pathogens in the early stages of B cell mediated (humoral) immunity before there is sufficient IgG.
  • Antibodies contribute to immunity in three ways: preventing pathogens from entering or damaging cells by binding to them (neutralization); stimulating removal of pathogens by macrophages and other cells by coating the pathogen (opsonization); and triggering destruction of pathogens by stimulating other immune responses such as the complement pathway.
  • The immune cell will then bind to the antibody's Fc tail instead of the pathogen itself, which speed up the process of finding pathogens to phagocytize.
  • Additionally, because antibodies have two or more paratopes, they can sometimes link pathogens together, which makes phagocytosis more efficient.

• Phagocytes

  • A receptor on the phagocyte's cell membrane binds to a foreign particle, such as a pathogenic microbe, or a toxin.
  • The Fc receptor is typically the receptor of use, which binds to antibodies that have opsonized (marked) a pathogen or toxin.
  • The engulfed pathogen is kept in a vacuole called a phagosome, which then binds to the lysosomes inside the cell.
  • These are the general mechanisms used by phagocytosis to engulf and kill pathogens, however some variations can occur.
  • For instance, other receptors may be used to engulf pathogens, and other non-oxidative methods (such as lysozyme) exist to kill the phagocytized pathogen.

• Skin and Mucosae (Surface Barriers)

  • The three layers of the skin provide a barrier to entry of the body through pathogens.
  • While the skin simply prevents pathogen entry, more specialized structures like the mucocilliary escalator in the trachea work by trapping pathogens in mucus secretions, and use cilia to push them out of the trachea to prevent entry into the lungs.
  • The barrier system also refers to chemical barriers that prevent pathogen entry.
  • The barrier system is the first line of defense against pathogen invasion, through it is not perfect.
  • Not every pathogen is caught nor inhibited in mucus, and some may infect the mucosal epithelium directly.

• Tonsils

  • The tonsils are one of the immune system's first line of defense against ingested or inhaled foreign pathogens.
  • They function similarly to other types of secondary lymphoid organs and also act to capture antigens from respiratory tract pathogens.
  • The primary function of the tonsils is to facilitate adaptive immune responses in the upper respiratory tract, which is one of the most common pathways for pathogen entry in the body.
  • In a way, the tonsils are the "first line of defense" against potential respiratory pathogens.
  • The tonsils contain specialized "M cells" that collect antigens produced by respiratory tract pathogens.

• Active and Passive Humoral Immunity

  • Secreted antibodies bind to antigens on the surfaces of invading pathogens, which flag them for destruction.
  • It also refers to the effector functions of antibodies, which include pathogen and toxin neutralization, classical complement activation, and opsonin promotion of phagocytosis and pathogen elimination.
  • Natural active immunity generally occurs as a result of infection with a pathogen, in which memory cells that remember the antigen of the infectious agent remain in the body.
  • During vaccination, the body is exposed to a weakened form of a pathogen that contains the same antigens as the live pathogen, but cannot mount an infection against the body in its weakened state.
  • Passive immunity provides immediate protection, but the body does not develop memory; therefore, the patient is at risk of being infected by the same pathogen later.

• Role of the Complement System in Immunity

  • The complement system is the ability of antibodies and phagocytic cells to remove pathogens from an organism.
  • The complement system helps or "complements" the ability of antibodies and phagocytic cells to clear pathogens from an organism.
  • The antibody binds to an antigen on the surface of a pathogen, activating the C1 complement protein.
  • The pathogenic antigen (such as LPS) activates C3 so it creates a C3B complex
  • It is an acute phase reactant produced in the liver and binds to the carbohydrates on the surfaces of many pathogens.