In search of the anti-rabbit

While working on a translation the other day, I happened to need to know what preposition the verb “to be constituted” takes (and don’t sit there looking so smug: do you know what preposition it takes?). Google, normally the fount of all knowledge, was uncharacteristically unhelpful with the matter, so I turned to the European Union’s online multilingual dictionary, IATE, where I typed in “costituito” (the Italian term that had thrown me) and got the shock of my life to be faced with this:

Chimica [EP]					Voce completa
IT	coniugato costituito da immunoglobulina anti-coniglio e isotiocianato di fluoresceina
	FITC
EN	FITC
	fluorescein isothiocyanate anti-rabbit immunoglobulin conjugate

In the midst of this lexical kaleidoscope, the only words that really swam into focus were “anti-rabbit”. So I decided to work with what I had and googled anti-rabbit. It turns out to be a term from the field of antibodies. And I was left well and truly speechless to discover, fourteen and a half million results later, that antibodies can be not only anti-rabbit but also anti-goat, anti-horse, anti-mouse, anti-rat, anti-sheep, anti-pig, anti-chicken, anti-donkey, anti-guinea-pig, anti-hamster and anti-cow (which is actually properly called anti-bovine). 

And it gets worse. Antibodies can also be goat anti-mouse, chicken anti-rat, donkey anti-pig, and all manner of startling combinations of animals.

But what does it all mean?

  

1)      Let’s start with immunoglobulin, which is another word for antibody.

An antibody (or immunoglobulin if you prefer) is a type of protein which functions within the immune system to identify and neutralise antigens.  They are produced by plasma cells, a type of white blood cell.

2)      What is an antigen?

An antigen is a foreign body which an antibody attacks.  Examples of antigens are microorganisms (e.g. bacteria, viruses, funghi and parasites), pollen, chemicals, bacterial toxins and tissue cells.

3)      What does an antibody look like?

An antibody looks like this:

but for the sake of comprehension, we will picture it like this:

It is made up of two heavy polypeptide chains (blue) and two light ones (pink) arranged in a Y shape.  For the most part, antibodies are all the same except for the tips of the Y (the light areas in the picture). These tips are the antigen binding sites – the parts of the antibody which attach themselves to the antigen, and they differ according to which antigen they bind to.

4)      What does an antibody do to an antigen?

An antibody has various methods of attack:

a)      Opsonisation

The antibody recognises and attaches itself to an antigen, then releases a chemical signal to attract phagocytic (devouring) cells to consume it.

b)      Neutralisation

Sometimes the antibody also neutralises the antigen directly by attaching itself to the part of the antigen that is used to cause infection, rendering it useless.

c)       Complement activation

The antibody calls phagocytic cells, and while it waits for them to arrive, it activates complement, a chain of proteins which helps destroy infected cells.

d)      Agglutination

Having two branches in its Y shape, the antibody can bind to two antigens.  So an antibody can join two antigens together, then another antibody can join another antigen to them, and so on, until a clump is formed. This clump becomes cumbersome and vulnerable to phagocytes.

An animation of neutralisation and opsonisation:

5)      Isn’t that amazing?

It is – when it works. But sometimes it doesn’t. Some immune disorders, for example, prevent the immune system producing the right antibodies or enough of them. Or with cancer, your immune system may not recognise the cancer cells as dangerous, because they are relatively similar to your body cells. Alternatively, it may recognise them as foreign but not be strong enough to fight them, or the immune system’s activity might be limited by substances given off by the cancer cells.

6)      Are we getting to the rabbits now?

Yes. Cases such as those described above can be treated by introducing foreign antibodies into the body. These antibodies are created in a laboratory by injecting animals with the antigen in question, inducing them to produce the appropriate antibodies. Mice are the animals most frequently used, but rabbits – and indeed goats, horses, rats, sheep, pigs, chickens, donkeys, guinea pigs, hamsters and cows – can also be used.

This is a clever idea in theory, but in practice, your body sometimes feels threatened by these foreign antibodies, and manufactures its own antibodies to attack them, producing an allergic reaction which can range from a rash to renal failure. These antibodies which you produce are called anti-mouse antibodies (or anti-rabbit or anti-chicken, or anti- whatever the animal in question is). And because you are human, they are called human anti-mouse (or human anti-chicken etc) antibodies. If you were a goat, the result would be goat anti-mouse antibodies. You get the idea.

Animals in our systems are not as infrequent as you might think. It is estimated that at least 10% of the general population carries some form of animal-derived antibodies, due to the widespread use of medicines manufactured using animal sera.

7)      Now we need to deal with fluorescein isothiocyanate. Stay with me…

Fluorescein is a dye which glows (“to fluoresce” means “to glow”), and it is used as a tracer (being introduced into a body or other system so that its distribution can be followed).

Isothiocyanates are a family of organic compounds, which are found in nature in certain strongly-flavoured vegetables such as horseradish and onions. (“Iso”=similar, “thio”=sulphur, “cyanate”=salt or ester of cyanic acid)These compounds can be synthesised, however, from, among other things, the fluorescein mentioned above.

Fluorescein isothiocyanate – the organic compound synthesised from fluorescein – is used to label and track cells, so that they can be identified under a microscope. It can be conjugated (connected) to antibodies, which help target specific proteins or structures (remember, antibodies are all about targeting: watch the video above again if you don’t remember).

8)      So in summary:

Fluorescein isothiocyanate anti-rabbit immunoglobulin conjugate need scare us no longer. We now know that it is an organic compound (isothiocyanate) derived from a fluorescing dye (fluorescein), connected (conjugated) to an antibody (immunoglobulin) which fights antibodies produced in rabbits (anti-rabbit).

9)      Where can I get it?

From Sigma Aldrich, purveyors of chemical and biochemical products. They advise you to store your fluorescein isothiocyanate anti-rabbit immunoglobulin conjugate as follows:

For continuous use, store at 2-8 °C for up to one month. For extended storage, the solution may be frozen in working aliquots.  Repeated freezing and thawing is not recommended.  Storage in "frost-free" freezers is not recommended.  If slight turbidity occurs upon prolonged storage, clarify the solution by centrifugation before use.

10)   And since you were probably wondering…

“Constituted by” and “constituted of” both exist. I went for “by” on this occasion.

SOURCES 

http://en.wikipedia.org/wiki/Polyclonal_antibodies

http://www.biology.arizona.edu/immunology/tutorials/antibody/structure.html

http://www.nlm.nih.gov/medlineplus/ency/article/002223.htm

http://www.nlm.nih.gov/medlineplus/ency/article/002224.htm

http://www.escience.ws/b572/L14/L14.htm

http://www.livestrong.com/article/19098-antibodies-work/

http://faculty.stcc.edu/AandP/AP/AP2pages/Units21to23/immune/abwork.htm

http://www.memidex.com/fluorescein

http://medical-dictionary.thefreedictionary.com/fluorescein

http://en.wikipedia.org/wiki/Fluorescein_isothiocyanate

http://www.news-medical.net/health/Antibody-What-is-an-Antibody.aspx

http://en.wikipedia.org/wiki/Fluorescein

http://www.cancer.org/Treatment/TreatmentsandSideEffects/TreatmentTypes/Immunotherapy/immunotherapy-immune-system

http://en.wikipedia.org/wiki/Human_anti-mouse_antibody