pathogen

Examples of pathogen in the following topics:

• Innate Immune Response

  • A host is the organism that is invaded and often harmed by a pathogen.
  • Mammalian immune systems evolved for protection from such pathogens.
  • Components of both immune systems constantly search the body for signs of pathogens.
  • When pathogens are found, immune factors are mobilized to the site of an infection.
  • Features of the immune system (e.g., pathogen identification, specific response, amplification, retreat, and remembrance) are essential for survival against pathogens.

• Plant Defenses Against Pathogens

  • Plants defend against pathogens with barriers, secondary metabolites, and antimicrobial compounds.
  • Pathogens are agents of disease.
  • Both protect plants against pathogens.
  • Additionally, plants have a variety of inducible defenses in the presence of pathogens.
  • Plants can close stomata to prevent the pathogen from entering the plant.

• Physical and Chemical Barriers

  • The innate immune response has physical and chemical barriers that exist as the first line of defense against infectious pathogens.
  • In the innate immune response, any pathogenic threat triggers a consistent sequence of events that can identify the type of pathogen and either clear the infection independently or mobilize a highly-specialized adaptive immune response.
  • Pathogens are killed or inactivated on the skin by desiccation (drying out) and by the skin's acidity.
  • Some pathogens have evolved specific mechanisms that allow them to overcome physical and chemical barriers.
  • Some of these include the low pH of the stomach, which inhibits the growth of pathogens; blood proteins that bind and disrupt bacterial cell membranes; and the process of urination, which flushes pathogens from the urinary tract.

• The Complement System

  • The innate immune system serves as a first responder to pathogenic threats that bypass natural physical and chemical barriers of the body.
  • An array of approximately 20 types of soluble proteins, called a complement system, functions to destroy extracellular pathogens.
  • They serve as a marker to indicate the presence of a pathogen to phagocytic cells, such as macrophages and B cells, to enhance engulfment.
  • These structures destroy pathogens by causing their contents to leak .
  • Pathogens lacking these regulatory proteins are lysed.

• Pathogen Recognition

  • Upon pathogen entry to the body, the innate immune system uses several mechanisms to destroy the pathogen and any cells it has infected.
  • When a pathogen enters the body, cells in the blood and lymph detect the specific pathogen-associated molecular patterns (PAMPs) on the pathogen's surface.
  • A macrophage is a large, phagocytic cell that engulfs foreign particles and pathogens.
  • Dendritic cells bind molecular signatures of pathogens, promoting pathogen engulfment and destruction.
  • A neutrophil is also a phagocytic leukocyte that engulfs and digests pathogens .

• Immunological Memory

  • The adaptive immune system has a memory component that allows for a rapid and large response upon re-invasion of the same pathogen.
  • As the infection is cleared and pathogenic stimuli subside, the effector cells are no longer needed; they undergo apoptosis.
  • Vaccination is based on the knowledge that exposure to noninfectious antigens, derived from known pathogens, generates a mild primary immune response .
  • When exposed to the corresponding pathogen to which an individual was vaccinated, the reaction is similar to a secondary exposure.
  • Vaccines, often delivered by injection into the arm, result in a secondary immune response if the vaccinated individual is later exposed to that pathogen.

• Humoral Immune Response

  • The humoral immune response defends against pathogens that are free in the blood by using antibodies against pathogen-specific antigens.
  • The humoral immune response fights pathogens that are free in the bodily fluids, or "humours".
  • It relies on antigens (which are also often free in the humours) to detect these pathogens.
  • Antibody neutralization can prevent pathogens from entering and infecting host cells.
  • The neutralized antibody-coated pathogens can then be filtered by the spleen to be eliminated in urine or feces.

• Antibody Functions

  • Antibodies, part of the humoral immune response, are involved in pathogen detection and neutralization.
  • The antibodies they secrete are particularly significant against extracellular pathogens and toxins.
  • Antibodies coat extracellular pathogens and neutralize them by blocking key sites on the pathogen that enhance their infectivity, such as receptors that "dock" pathogens on host cells .
  • The neutralized antibody-coated pathogens can then be filtered by the spleen and eliminated in urine or feces.
  • It would be expected to present a more challenging defense against the pathogen corresponding to the specific antigen.

• Antigen-presenting Cells: B and T cells

  • However, adaptive immunity is more specific to an invading pathogen and can fight back much more quickly than the innate response if it has seen the pathogen before.
  • Adaptive immunity occurs after exposure to an antigen either from a pathogen or a vaccination.
  • Upon infection, activated T and B cells that have surface binding sites with specificity to the molecules on the pathogen greatly increase in number and attack the invading pathogen.
  • Their attack can kill pathogens directly or they can secrete antibodies that enhance the phagocytosis of pathogens and disrupt the infection.
  • Meanwhile, T cell receptors are responsible for the recognition of pathogenic antigens by T cells .

• Fungi as Plant, Animal, and Human Pathogens

  • From crop and food spoilage to severe infections in animal species, fungal parasites and pathogens are wide spread and difficult to treat.
  • Many plant pathogens are fungi that cause tissue decay and eventual death of the host .
  • In addition to destroying plant tissue directly, some plant pathogens spoil crops by producing potent toxins.
  • Smuts, rusts, and powdery or downy mildew are other examples of common fungal pathogens that affect crops.
  • Give examples of fungi that are plant and animal parasites and pathogens