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Learning objectives

  • Describe how enzymes in body fluids provide protection against infection or disease
  • List and describe the function of antimicrobial peptides, complement components, cytokines, and acute-phase proteins
  • Describe similarities and differences among classic, alternate, and lectin complement pathways

In addition to physical defenses, the innate nonspecific immune system uses a number of chemical mediators that inhibit microbial invaders. The term “chemical mediators” encompasses a wide array of substances found in various body fluids and tissues throughout the body. Chemical mediators may work alone or in conjunction with each other to inhibit microbial colonization and infection.

Some chemical mediators are endogenously produced, meaning they are produced by human body cells; others are produced exogenously, meaning that they are produced by certain microbes that are part of the microbiome. Some mediators are produced continually, bathing the area in the antimicrobial substance; others are produced or activated primarily in response to some stimulus, such as the presence of microbes.

Chemical and enzymatic mediators found in body fluids

Fluids produced by the skin include examples of both endogenous and exogenous mediators. Sebaceous glands in the dermis secrete an oil called sebum that is released onto the skin surface through hair follicles. This sebum is an endogenous mediator, providing an additional layer of defense by helping seal off the pore of the hair follicle, preventing bacteria on the skin’s surface from invading sweat glands and surrounding tissue ( [link] ). Certain members of the microbiome, such as the bacterium Propionibacterium acnes and the fungus Malassezia , among others, can use lipase enzymes to degrade sebum, using it as a food source. This produces oleic acid , which creates a mildly acidic environment on the surface of the skin that is inhospitable to many pathogenic microbes. Oleic acid is an example of an exogenously produced mediator because it is produced by resident microbes and not directly by body cells.

A micrograph and diagram both show a large hair follicle (a vase-shaped pocket) with a hair projecting out past the epidermis. On the side of the hair follicle is the sebaceous gland, which is a lumpy structure.
Sebaceous glands secrete sebum, a chemical mediator that lubricates and protect the skin from invading microbes. Sebum is also a food source for resident microbes that produce oleic acid, an exogenously produced mediator. (credit micrograph: Micrograph provided by the Regents of University of Michigan Medical School © 2012)

Environmental factors that affect the microbiota of the skin can have a direct impact on the production of chemical mediators. Low humidity or decreased sebum production, for example, could make the skin less habitable for microbes that produce oleic acid, thus making the skin more susceptible to pathogens normally inhibited by the skin’s low pH. Many skin moisturizers are formulated to counter such effects by restoring moisture and essential oils to the skin.

The digestive tract also produces a large number of chemical mediators that inhibit or kill microbes. In the oral cavity, saliva contains mediators such as lactoperoxidase enzymes, and mucus secreted by the esophagus contains the antibacterial enzyme lysozyme . In the stomach, highly acidic gastric fluid kills most microbes. In the lower digestive tract, the intestines have pancreatic and intestinal enzymes, antibacterial peptides (cryptins), bile produced from the liver, and specialized Paneth cells that produce lysozyme. Together, these mediators are able to eliminate most pathogens that manage to survive the acidic environment of the stomach.

Questions & Answers

Explain about enzyme transportation
Shahla Reply
Enzyme transportation
it looks reallllyyyyy coooooooollll. i love enzymes theyre so cooll and i also like protein transportation so i think it would be really cool so an enzyme transport something so ill do some research and come back to ya in that
what is the infectious disease process
Patience Reply
what are differences between endotoxins and exotoxins
sabote Reply
endo toxins work in the nuceus. i think
tell me if im right tho
Exotoxins are toxic substances secreted by bacteria and released outside the cell. Both gram positive and gram negative bacteria can produce and secrete exotoxins. Whereas Endotoxins are bacterial toxins consisting of lipids that are located within a cell. Only lysed gram negatives.
Remebr the Lipid A portion of LPS is what's toxic.
oh yeah. thanks
Your welcome :)
How did you learn this?
For me personally the best book is 'microbiology made ridiculously simple'
I got my basics from there and slowly added information from other sources.
thats cool! yeah i like microbiology too! especially the molecular proteins theyre sooooooooooo cool!
what are the prokaryotic
Lungu Reply
prokaraytotic is a unicellular organizm that lacks membrane bound nucleus
and whats eukaryotic
eukaryotic cell are cell which contain anuclues and organells
eukaryotes are the cells that have organells which are protected by membranes
eukaryotic is are multicellular organisms which are open nucleus.
Explain on the Francisco reddi did to prove the theory of spontaneous generation
Diana Reply
what is parasite
Abdirizack Reply
parasite are organisms feeds on a host for food and survival.e.g round worm for animal, Dodder for plant parasites.
parasite are organisms that feeds on a host for food and survival.e.g round worm for animal and mistletoe for plant parasites.
parasite are organisms that feed on their host
designing of aseptic area
Aashish Reply
I don't know
what is rickettsia
what is microbiology
Is the science that works with microorganisms.
richettsa is small microorganisms that cause disease in human like typhus; they are like viruses that can grow only inside living cells, they're transmitted by mites, ticks or lices.
what is plasmid?
plasmid is extra chromosomal body present in bacteria...which have additional genetic functions example... antibiotic resistance genes....etc etc
state the theory of spontaneous generation of micro oranisms and germ theory of disease
what are the advantages of high note numerical aperture
Genius Reply
list if non flagellated pritozoa
Mepung Reply
Can someone that's understanding of the Kreb Cycle please explain & breakdown it down to me in the simplest way without giving me the dictionary version or Google version. Basically in there own words of knowledge....!
please can someone help explain positive and negative feedback in simple term
negative feedback is the arresting of reaction or reverse of the reaction according to the response and postive feed back is the direct response without reversing or arresting a reaction.
pls can someone explained Kinney stone in memorising in shot time
what tyoebif microorganism will be killed by antibiotic trwatmeant
Mary Reply
I don't really don't understand aerobic respiration anaerobic respiration and fermentation. Can someone explain & breakdown this in the simplest way please.
Anaerobic Respiration in which foodstuffs are partially oxidized, with the release of chemical energy, in a process not involving atmospheric oxygen, such as alcoholic fermentation, in which one of the end products is ethanol.
aerobic respiration A type of respiration in which foodstuffs are completely oxidized to carbon dioxide and water, with the release of chemical energy, in a process requiring atmospheric oxygen.
please can someone explain what pseudomonas species and biofilm is?
Fermentation is the growth of cells or microorganisms in bioreactors (fermenters) to synthesize special products. Fermentation in biochemistry refers to the biodegradation of carbon compounds by cells or organisms under anaerobic (lack of oxygen) conditions.
Please under which conditions does pathogens become established in the human tissues and can cause diseases
please the life cycle of plasmodium parasite
who is John Needham
Mary Reply
John Needham is one of the researcher in microbiology. He also experimented when scientists did not believe animals could arise spontaneously ,but did believe microbes could.
okay is he late
by the way what are the list of courses offered by a newly admitted student for microbiology
Needham's experiments with beef gravy and infusions of plants material reinforced this idea.
what drugs are given to a person with Otis nerve problem(ear problem)
Gum Reply
good morning to you all.
Muhammad Reply
Dr.A.K.S.P.G. college Akbarpur Ambedkar Nagar
Shailesh Vishwakarma BSc 1st year
Practice MCQ 5

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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