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There are numerous other AMPs throughout the body. The characteristics of a few of the more significant AMPs are summarized in [link] .
| Characteristics of Selected Antimicrobial Peptides (AMPs) | ||||
|---|---|---|---|---|
| AMP | Secreted by | Body site | Pathogens inhibited | Mode of action |
| Bacteriocins | Resident microbiota | Gastrointestinal tract | Bacteria | Disrupt membrane |
| Cathelicidin | Epithelial cells, macrophages, and other cell types | Skin | Bacteria and fungi | Disrupts membrane |
| Defensins | Epithelial cells, macrophages, neutrophils | Throughout the body | Fungi, bacteria, and many viruses | Disrupt membrane |
| Dermicidin | Sweat glands | Skin | Bacteria and fungi | Disrupts membrane integrity and ion channels |
| Histatins | Salivary glands | Oral cavity | Fungi | Disrupt intracellular function |
Many nonspecific innate immune factors are found in plasma , the fluid portion of blood. Plasma contains electrolytes, sugars, lipids, and proteins, each of which helps to maintain homeostasis (i.e., stable internal body functioning), and contains the proteins involved in the clotting of blood. Additional proteins found in blood plasma, such as acute-phase proteins, complement proteins, and cytokines, are involved in the nonspecific innate immune response.
There are two terms for the fluid portion of blood: plasma and serum. How do they differ if they are both fluid and lack cells? The fluid portion of blood left over after coagulation (blood cell clotting) has taken place is serum . Although molecules such as many vitamins, electrolytes, certain sugars, complement proteins, and antibodies are still present in serum, clotting factors are largely depleted. Plasma, conversely, still contains all the clotting elements. To obtain plasma from blood, an anticoagulant must be used to prevent clotting. Examples of anticoagulants include heparin and ethylene diamine tetraacetic acid (EDTA). Because clotting is inhibited, once obtained, the sample must be gently spun down in a centrifuge. The heavier, denser blood cells form a pellet at the bottom of a centrifuge tube, while the fluid plasma portion, which is lighter and less dense, remains above the cell pellet.
The acute-phase proteins are another class of antimicrobial mediators. Acute-phase proteins are primarily produced in the liver and secreted into the blood in response to inflammatory molecules from the immune system. Examples of acute-phase proteins include C-reactive protein , serum amyloid A , ferritin , transferrin , fibrinogen , and mannose-binding lectin . Each of these proteins has a different chemical structure and inhibits or destroys microbes in some way ( [link] ).
| Some Acute-Phase Proteins and Their Functions | |
|---|---|
| C-reactive protein | Coats bacteria (opsonization), preparing them for ingestion by phagocytes |
| Serum amyloid A | |
| Ferritin | Bind and sequester iron, thereby inhibiting the growth of pathogens |
| Transferrin | |
| Fibrinogen | Involved in formation of blood clots that trap bacterial pathogens |
| Mannose-binding lectin | Activates complement cascade |
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