Chemical defenses are a crucial aspect of the innate immune system, providing protection against infection and disease. These defenses can be categorized into two main types: endogenous mediators, which are produced by the body’s own cells, and exogenous mediators, which are produced by resident microbes that are part of the microbiome.
Key Facts
- Chemical warnings and alarm pheromones: Many marine invertebrates, such as clams and blue shell crabs, use chemical warnings and alarm pheromones as a defensive strategy.
- Phagomimicry: Sea hares employ a form of chemical defense called phagomimicry, where they mimic the chemical defenses of their prey to deter predators.
- Enzymes in body fluids: The innate immune system of organisms uses chemical mediators, such as enzymes, to inhibit microbial invaders. These enzymes can be found in body fluids like saliva, mucus, and urine.
- Sebum: Sebum, an oil secreted by sebaceous glands in the skin, acts as a chemical mediator to protect the skin from invading microbes. It also creates a mildly acidic environment that is inhospitable to many pathogenic microbes.
- Oleic acid: Oleic acid is an exogenously produced mediator that is produced by resident microbes on the skin. It helps create an acidic environment on the skin’s surface, which inhibits the growth of pathogenic microbes.
- Lactoperoxidase enzymes: Saliva contains lactoperoxidase enzymes, which have antibacterial properties and help inhibit the growth of microbes in the oral cavity.
- Lysozyme: Lysozyme is an antibacterial enzyme found in mucus secreted by the esophagus and produced by specialized cells in the intestines. It helps kill or inhibit the growth of bacteria.
Enzymes in Body Fluids: A Chemical Barrier
Body fluids, such as saliva, mucus, urine, and sebum, contain various chemical mediators that exhibit antimicrobial properties. Sebum, an oil secreted by sebaceous glands in the skin, acts as a protective barrier against invading microbes. It also helps create a mildly acidic environment on the skin’s surface, which inhibits the growth of pathogenic microbes. Oleic acid, an exogenously produced mediator produced by resident microbes on the skin, contributes to the acidic environment and further inhibits microbial growth.
Saliva contains lactoperoxidase enzymes, which have antibacterial properties and help inhibit the growth of microbes in the oral cavity. Lysozyme, an antibacterial enzyme found in mucus secreted by the esophagus and produced by specialized cells in the intestines, also plays a role in killing or inhibiting the growth of bacteria.
Antimicrobial Peptides: A Diverse Arsenal of Defense
Antimicrobial peptides (AMPs) are a class of nonspecific cell-derived mediators with broad-spectrum antimicrobial properties. These peptides can be produced routinely by the body or primarily in response to the presence of an invading pathogen. AMPs may induce cell damage in microorganisms by inflicting damage to membranes, destroying DNA and RNA, or interfering with cell-wall synthesis. Some notable AMPs include defensins, bacteriocins, dermicidin, cathelicidin, and histatins.
Plasma Protein Mediators: A Cascade of Protection
Plasma, the fluid portion of blood, contains various proteins that serve as chemical mediators, including acute-phase proteins, complement proteins, and cytokines. Acute-phase proteins, such as C-reactive protein, serum amyloid A, ferritin, transferrin, fibrinogen, and mannose-binding lectin, are produced in the liver and secreted into the blood in response to inflammatory molecules from the immune system. These proteins inhibit or destroy microbes in various ways.
Complement proteins, a group of more than 30 proteins, circulate as precursor proteins in blood and become activated in the presence of microorganisms. This process, known as complement activation, can be triggered through three different mechanisms: the alternative, classical, and lectin pathways. The complement system provides protective outcomes such as opsonization, inflammation, chemotaxis, and cytolysis.
Cytokines, soluble proteins that act as communication signals between cells, play a crucial role in the nonspecific innate immune response. They stimulate the production of chemical mediators, cell proliferation, cell differentiation, inhibition of cell division, apoptosis, and chemotaxis. Interleukins, chemokines, and interferons are important classes of cytokines.
Inflammation-Eliciting Mediators: A Symphony of Signals
Inflammation-eliciting mediators contribute to the inflammatory response, which is a key aspect of the innate immune system. Histamine, a proinflammatory compound released by mast cells and basophils, promotes vasodilation, bronchoconstriction, smooth muscle contraction, increased secretion, and mucus production. Leukotrienes, lipid-based proinflammatory mediators, are more potent and longer-lasting than histamine. Prostaglandins, also produced by mast cells, promote inflammation and fever. Bradykinin, another inflammatory mediator, increases vasodilation and vascular permeability, leading to edema.
Conclusion
Chemical defenses are a diverse and multifaceted aspect of the innate immune system, providing protection against infection and disease. These defenses include enzymes in body fluids, antimicrobial peptides, plasma protein mediators, and inflammation-eliciting mediators. These chemical mediators work together to inhibit microbial colonization and infection, ensuring the body’s defense against harmful pathogens.
References
- “Chemical Defense – Wikipedia.” https://en.wikipedia.org/wiki/Chemical_defense. Accessed 10 Mar. 2023.
- “Chemoreception – Chemical Defense, Signaling, Receptors | Britannica.” https://www.britannica.com/science/chemoreception/Chemical-defense. Accessed 10 Mar. 2023.
- “17.2: Chemical Defenses – Biology LibreTexts.” https://bio.libretexts.org/Bookshelves/Microbiology/Microbiology_(OpenStax)/17%3A_Innate_Nonspecific_Host_Defenses/17.02%3A_Chemical_Defenses. Accessed 10 Mar. 2023.
FAQs
What are chemical defenses?
Chemical defenses are a multifaceted approach employed by organisms to protect themselves against infection and disease. These defenses can be endogenous (produced by the organism’s own cells) or exogenous (produced by resident microbes).
What are some examples of chemical defenses in the human body?
Examples of chemical defenses in the human body include enzymes in body fluids (e.g., lysozyme in saliva and mucus), antimicrobial peptides (e.g., defensins and bacteriocins), plasma protein mediators (e.g., complement proteins and cytokines), and inflammation-eliciting mediators (e.g., histamine and prostaglandins).
How do enzymes in body fluids act as chemical defenses?
Enzymes in body fluids, such as lysozyme, lactoperoxidase, and digestive enzymes, exhibit antimicrobial properties. They can kill or inhibit the growth of microbes by damaging their cell walls, membranes, or DN
What are antimicrobial peptides (AMPs), and how do they contribute to chemical defense?
Antimicrobial peptides (AMPs) are a diverse group of cell-derived mediators with broad-spectrum antimicrobial activity. They can induce cell damage in microorganisms by disrupting membranes, destroying nucleic acids, or interfering with cell wall synthesis.
What is the complement system, and how does it participate in chemical defense?
The complement system is a group of plasma proteins that become activated in the presence of microorganisms. This activation leads to a cascade of events that result in the opsonization of pathogens, chemotaxis of leukocytes, inflammation, and cytolysis through the formation of a membrane attack complex (MAC).
What are cytokines, and how do they contribute to chemical defense?
Cytokines are soluble proteins that act as communication signals between cells. They play a crucial role in the nonspecific innate immune response by stimulating the production of chemical mediators, cell proliferation, cell differentiation, apoptosis, and chemotaxis.
What are inflammation-eliciting mediators, and how do they contribute to chemical defense?
Inflammation-eliciting mediators are chemical substances that contribute to the inflammatory response, a key aspect of the innate immune system. These mediators, such as histamine, leukotrienes, prostaglandins, and bradykinin, promote vasodilation, increased vascular permeability, and the recruitment of immune cells to the site of infection or tissue damage.
How do chemical defenses work together to protect the body?
Chemical defenses work together in a coordinated manner to protect the body against infection and disease. Enzymes in body fluids provide a first line of defense by directly killing or inhibiting the growth of microbes. Antimicrobial peptides and plasma protein mediators, such as the complement system and cytokines, enhance the immune response by opsonizing pathogens, attracting immune cells, and promoting inflammation. Inflammation-eliciting mediators contribute to the inflammatory response, which helps to isolate and eliminate pathogens and promote tissue repair.