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Learning objectives

  • Describe various types of assays used to find antigen-antibody complexes
  • Describe the circumstances under which antigen-antibody complexes precipitate out of solution
  • Explain how antibodies in patient serum can be used to diagnose disease

Laboratory tests to detect antibodies and antigens outside of the body (e.g., in a test tube) are called in vitro assays. When both antibodies and their corresponding antigens are present in a solution, we can often observe a precipitation reaction in which large complexes (lattices) form and settle out of solution. In the next several sections, we will discuss several common in vitro assays.

Precipitin reactions

A visible antigen-antibody complex is called a precipitin , and in vitro assays that produce a precipitin are called precipitin reactions . A precipitin reaction typically involves adding soluble antigens to a test tube containing a solution of antibodies. Each antibody has two arms, each of which can bind to an epitope. When an antibody binds to two antigens, the two antigens become bound together by the antibody. A lattice can form as antibodies bind more and more antigens together, resulting in a precipitin ( [link] ). Most precipitin tests use a polyclonal antiserum rather than monoclonal antibodies because polyclonal antibodies can bind to multiple epitopes, making lattice formation more likely. Although mAbs may bind some antigens, the binding will occur less often, making it much less likely that a visible precipitin will form.

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Polyclonal antiserum binds to multiple epitopes on an antigen, leading to lattice formation that results in a visible precipitin. Monoclonal antibodies can only bind to a single epitope; therefore, less binding occurs and lattice formation generally does not occur.

The amount of precipitation also depends on several other factors. For example, precipitation is enhanced when the antibodies have a high affinity for the antigen. While most antibodies bind antigen with high affinity, even high-affinity binding uses relatively weak noncovalent bonds, so that individual interactions will often break and new interactions will occur.

In addition, for precipitin formation to be visible, there must be an optimal ratio of antibody to antigen. The optimal ratio is not likely to be a 1:1 antigen-to-antibody ratio; it can vary dramatically, depending on the number of epitopes on the antigen and the class of antibody. Some antigens may have only one or two epitopes recognized by the antiserum, whereas other antigens may have many different epitopes and/or multiple instances of the same epitope on a single antigen molecule.

[link] illustrates how the ratio of antigen and antibody affects the amount of precipitation. To achieve the optimal ratio, antigen is slowly added to a solution containing antibodies, and the amount of precipitin is determined qualitatively. Initially, there is not enough antigen to produce visible lattice formation; this is called the zone of antibody excess. As more antigen is added, the reaction enters the equivalence zone (or zone of equivalence), where both the optimal antigen-antibody interaction and maximal precipitation occur. If even more antigen were added, the amount of antigen would become excessive and actually cause the amount of precipitation to decline.

Questions & Answers

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compare and contrast similar structures found in prokaryotic and eukaryotic cells
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genital herpes caused by a virus called herpe simplex virus
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classification of gram positive
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classify gram positive
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gram positive staph is further differentiated on sensitivity test and manitol salt fermentation test while gram positive strep is differentiated on hemolysis pattern
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taxonomy
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oils and waxes are not sterilized in autoclave
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what is the function of paraffin
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@ MAHI because they can grow all over the media from surface to the bottom as they can utilize oxygen or conduct fermentation in its absence.
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2.@MAHI Autoclave uses steam under pressure. The steam cannot penetrate through oil and wax. Thus, dry heat sterilization is preferred than autoclave .
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how nutirent agar can converted into blood agar
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take a nutrient agar ........and add 5ml blood and put in it ...........!
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nutrient agar +blood 5ml+ distilled water =blood agar .
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why agar is not a neutrient source?
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because it's a general purpose agar only use for growing bacteria
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way is antigen
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what is antigen
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antigen is a foreign body that cause activation of antibody?
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Antigen is a toxin or other foreign substance which induces an immune response in the body, especially the production of antibodies.
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a science that studies about the drug
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Work hard
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bacteria kya hai
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content of their cell wall
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koi mujhse basic microbiology ki study k Lea book suggest kro .
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Harley prescott
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1. long term exposure to diseases, that the body immunity weakens.
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2. Nature Of some diseases to weaken body immunity such as, AIDS.
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3. Use of immuno-suppresive drugs.
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Low immune is the major cause eg for kaposis sarcoma
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suitable conditions e.g temp,
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morphological and genetic classification of bacteria
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morphologycal is defined as relating to the branch of biology that deals with the form of living organisms,and with relationship between their structures.
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relating to the form or structure of things .
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iam from iraq
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is the study of invisible micro organism
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microbiology is the study of very too small organisms which we can't see with naked eyes ......in other words ....study of microorganism is called microbiology.
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Hello! How Can Microorganisms Be Isolated From The Skin?.. 5 ways if possible. (briefly)
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from skin swabbing is the prefer method worldwide
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thanks Muhammad Nauman very much!
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Any question or ideas, Meek?😊
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and if a patient have any blister or abscess on the skin then first cut the blister or abscess. inside material is taking by syringe.
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in case of fingernail or toenails simply cut a small piece of nail and culture on the appropriate media at a required temperature and time
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Again, thanks Mr. Muhammad! I appreciate the help.
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what are the media use for skin swab?
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blood and macckonkey mostly usededia for skin bacteria
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used media*
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@ SIEH mostly fungal infection occurs in skin so SDA ( Sabouraud Dextrose Agar) or MEA ( Malt extract agar) are common.
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Sieh-Mlanwin
Microbiologicam source of vitamins
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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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