Defense Mechanisms

Examples of Defense Mechanisms in the following topics:

• Plant Defenses Against Herbivores

  • Plants defend against herbivores with mechanical wounding, barriers, secondary metabolites, and attraction of parasitoids.
  • If the first line of defense is breached, the plant must resort to a different set of defense mechanisms, such as toxins and enzymes.
  • Mechanical wounding and predator attacks activate defense and protective mechanisms in the damaged tissue and elicit long-distancing signaling or activation of defense and protective mechanisms at sites farther from the injury location.
  • Some defense reactions occur within minutes, while others may take several hours.
  • The spines on cactus plants are modified leaves that act as a mechanical defense against predators.

• Predation, Herbivory, and the Competitive Exclusion Principle

  • These defenses may be mechanical, chemical, physical, or behavioral.
  • This type of defensive mechanism is called aposematic coloration, or warning coloration .
  • The (a) honey locust tree (Gleditsia triacanthos) uses thorns, a mechanical defense, against herbivores, while the (b) Florida red-bellied turtle (Pseudemys nelsoni) uses its shell as a mechanical defense against predators.
  • (d) The North American millipede (Narceus americanus) uses both mechanical and chemical defenses: when threatened, the millipede curls into a defensive ball, producing a noxious substance that irritates eyes and skin.
  • Distinguish between predation and herbivory and describe defense mechanisms against each

• Plant Defenses Against Pathogens

  • A plant's exterior protection can be compromised by mechanical damage, which may provide an entry point for pathogens.
  • If the first line of defense is breached, the plant must resort to a different set of defense mechanisms, such as toxins and enzymes.
  • Additionally, plants have a variety of inducible defenses in the presence of pathogens.
  • Mechanical wounding and predator attacks activate defense and protective mechanisms in the damaged tissue and elicit long-distancing signaling or activation of defense and protective mechanisms at sites farther from the injury location.
  • Some defense reactions occur within minutes, while others may take several hours.

• Biofilms and Disease

  • Biofilms, complex colonies of bacteria acting as a unit in their release of toxins, are highly resistant to antibiotics and host defense.
  • Once established, they are very difficult to destroy as they are highly resistant to antimicrobial treatments and host defense.
  • In healthcare environments, biofilms grow on hemodialysis machines, mechanical ventilators, shunts, and other medical equipment.
  • They are rarely resolved by host defense mechanisms.

• Host Range

  • The defenses mounted by the host may act directly on the virus or indirectly on virus replication by altering or killing the infected cell.
  • Non-specific host defenses function early in an encounter with a virus to prevent or limit infection, while the specific host defenses function after infection in recovery to provide immunity for subsequent challenges.
  • The host defense mechanisms involved in a particular viral infection will vary depending on the virus, dose, and portal of entry.
  • These represent the first line of defense, which functions to prevent or limit infection Examples of natural barriers include but are not limited to skin, the expression of surface receptors such as CD4, complement receptors, glycophorin, intercelullar adhesion molecule 1 (ICAM-1) , mucus, a ciliated epithelium, low pH, and humoral and cellular components.

• Herbivory and Pollination

  • Herbivory has favored the development of defense mechanisms in plants and avoidance of those defense mechanisms in animals.
  • Coevolution of herbivores and plant defenses is observed in nature.
  • Spines and thorns deter most animals, except for mammals with thick fur; some birds have specialized beaks to get past such defenses .

• Direct Damage

  • Direct damage to the host is a general mechanism utilized by pathogenic organisms to ensure infection and destruction of the host cell.
  • Direct damage to the host is a general mechanism utilized by pathogenic organisms to ensure infection and destruction of the host cell.
  • The ability to manipulate the process of phagocytosis is a mechanism often utilized by bacteria to ensure they effectively invade a host.
  • Phagocytosis is a process utilized by phagocytes (white blood cells) as a defense mechanism to protect from foreign bodies.
  • The mechanism(s) utilized by pathogens to avoid phagocytosis include avoiding both contact and engulfment.

• Antimicrobial Peptides

  • A first line of defense against pathogenic insult is called the innate immune system, which is followed by acquired immune responses associated with the activation of T and B cells aimed against specific antigens.
  • In contrast to the clonal, acquired adaptive immunity, endogenous peptide antibiotics or antimicrobial peptides provide a fast and energy-effective mechanism as front-line defense.
  • Once in a target microbial membrane, the peptide kills target cells through diverse mechanisms.

• Physical and Chemical Barriers

  • The innate immune response has physical and chemical barriers that exist as the first line of defense against infectious pathogens.
  • The adaptive immune response expands over time, storing information about past infections and mounting pathogen-specific defenses.
  • The skin is considered the first defense of the innate immune system; it is the first of the nonspecific barrier defenses.
  • Some pathogens have evolved specific mechanisms that allow them to overcome physical and chemical barriers.
  • Once inside, the body still has many other defenses, including chemical barriers.

• The Complement System and Heart Disease

  • In autoimmune heart diseases, the body's immune defense system mistakes its own cardiac antigens as foreign, and attacks them.
  • Autoimmune heart diseases result when the body's own immune defense system mistakes cardiac antigens as foreign, and attacks them, leading to inflammation of the heart as a whole, or in parts.
  • A typical mechanism of autoimmunity is autoantibodies, or auto-toxic T-lymphocyte mediated tissue destruction.