Competitive ELISA

The fourth type of ELISA is competitive ELISA. As the name suggest there is going to be a competition between someone. Now let�s see between whom is this competition exactly going to be.

Competitive ELISA

Let�s take an example wherein we have to detect HIV antibodies from a serum sample.

For detection of HIV antibodies, the wells of micro titre plate are coated with HIV antigen followed by incubation of antibodies from the sample. After incubation detection antibodies specific to HIV antigens are added.

Now, if the sample contains HIV antibodies then antigen-antibody complexes are formed. No antigen  is left for detection antibody to bind.

Hence, these detection antibodies remain free and are washed off.  Addition of substrate to such a well gives no colour change indicating a positive result.

On the other hand, if the sample does not contain HIV antibodies then there is no antigen-antibody complex formed. Thus, the detection antibodies bind to the antigen which will show a colour change on addition of substrate indicating a negative result.

Thus, competitive ELISA involves a competition between detection antibody and sample antibody to bind with the sample antigen.

Also, in other types of ELISA colour change detected a positive result and no colour change detected a negative result whereas in competitive ELISA it�s exactly opposite!

Written by Komal M Kadam
Illustration by Immense Immunology Insight

Immunoglobulin A and IgA deficiency mnemonic

IgA occurs as a monomer in the bloodstream and as a dimer when secreted (linked by the secretory component or a J chain attained from epithelial cells before secretion).

IgA is secreted onto mucosal surfaces (gastrointestinal, genitourinary, and respiratory) to block attachment of pathogens to mucous membranes.

Mnemonic: �ABCDE�
A: Alone (Monomer)
B: in Blood
C: Component (Secretory component) or Chain (J chain) makes
D: Dimer
E: in Epithelial surfaces

What happens in IgA deficiency? Mnemonic!

The Immune System

Hello...

I don't know why one is so often tempted to address an audience, particularly one that is invisible and possibly imaginary. Anyway. Hello all of you out there who are attracted by the title. I am a scientist studying the immune system, and while i may have issues with life in science and the conduct of it, not to mention the establishment, I find the immune system fascinating. So I've decided to write about it. I read a lot of papers (at least I should) published in the immunology journals of today, and often I find things that are so interesting that I just want to discuss them. So I plan to summarize, try to explain and wonder about some of the coool things I read about in immunology

I do take requests, let me know if there's something you'd like me to post about in the comments. Always, I am NOT a medical professional, these are just my personal opinions, formed by the reading of published journal papers. They are not representative of anything other than my private personal opinions. They are shaped by my background in research, and my specialties. I am not omniscient, so I do not know or understand everything.

That said, let the immunology begin!

Direct ELISA

Direct ELISA is performed by attaching the sample antigens on a surface (walls of wells) then a specific antibody is applied so that it can bind to its corresponding antigen.

Direct ELISA

The antibodies used in ELISA are special they are known as Detection antibodies. These antibodies have an enzyme linked on its surface. The detection antibody being specific for a particular antigen it will bind only if that particular antigen is present in the sample.

After applying antibodies the next step is to wash off the unbound antibodies.

Now, there are 2 possibilities

1. The sample is positive for a particular antigen: In this case, it will have detection antibodies bound to it. The sample is then treated with the substrate of enzyme linked to the detection antibody. The enzyme converts the substrate into a product, which will give a colour change.

This colour change is directly proportional to the amount of antigen present in the given sample.

2. The sample is negative for a particular antigen: In this case, all the detection antibodies will be washed off as the specific antigen is absent. The enzyme bound to the detection antibody will also be lost. Hence, when substrate is added it will not be converted into product, giving us no colour change.

This is how direct ELISA works!

Written by Komal Kadam
Illustration by Immense Immunology Insight