Thread: Immunology: Why can't small molecules trigger allergic reactions?

Some small molecules such as penicillin cannot trigger an allergic response themselves (haptens). But why is it that the IgE can't be triggered by small molecules ( penicillin monomer, ethanol, water, carbon dioxide) ? I thought it was the shape that was required, not size, to trigger a reaction.

I don't know, why can't we start a boxing match with a Plasmodium vivax schizont?

Originally Posted by FrankBaker

Some small molecules such as penicillin cannot trigger an allergic response themselves (haptens). But why is it that the IgE can't be triggered by small molecules ( penicillin monomer, ethanol, water, carbon dioxide) ? I thought it was the shape that was required, not size, to trigger a reaction.

Imagine having a 4 meter diameter metal hoop, to stop objects from going somewhere. A square, with the same surface as the hoop will never pass, neither will a pentagon or a triangle. Neither will a circle with 4,1 meter diameter. However, if you throw golfballs at it, they will all pass.


Point is, size does still matter. Immunoglobuline will still need a certain size, or it can't connect. And it needs at least 2 recognizable positions that do not occur in the body. This way this molecule needs to be of considerable size.


The "arms" on an immunoglobuline has a minimum detection size. I don't exactly know what it is, but this depends on the structure, the originality, and some rarer elements, such as sulfur, zinc or nickel.

Frank/gaia, whats your overall push with all the short immune system thread. you are clearly working towards a larger goal with these questions.

But brain receptors can bind to things such as melatonin, i.e very small molecules.

1. What is the minimum size?
2. Why is size of a molecule so important to an IgE when brain receptors have no issue with size?

The blood brain barrier is key to keeping a VERY tight control on what actually touches the brain.

Originally Posted by Paleoichneum

Frank/gaia, whats your overall push with all the short immune system thread. you are clearly working towards a larger goal with these questions.

I predict it will be "so you can spontaneously catch on fire."

I'm trying to refute this woman who says she can't drink anything containing water without going into shock.

Originally Posted by FrankBaker

I'm trying to refute this woman who says she can't drink anything containing water without going into shock.

Why? Is she scamming people? Does she form a threat for herself and/or others? Does she actively spread misinformation about her condition?

Nah, she leaves that to SHC nutjobs like "Frank"...

Originally Posted by FrankBaker

I'm trying to refute this woman who says she can't drink anything containing water without going into shock.

It's a simple fact that everything you eat contains water, even crackers. So to solve this, all she has to do is eat ice cream all day. But yeah, she is incorrect. Noone is allergic to water, but hypersensitive to water saturation and saline levels is a thing.

Crackers don't contain very much water at all. People allergic to latex can often handle small amounts of it naturally found in some fruits for example.

I'm asking why size is allegedly so important to IgE receptors, when there are protein receptors in the brain which can bind melatonin, and other very small, non-protein molecules.

Originally Posted by FrankBaker

Crackers don't contain very much water at all. People allergic to latex can often handle small amounts of it naturally found in some fruits for example.

I'm asking why size is allegedly so important to IgE receptors, when there are protein receptors in the brain which can bind melatonin, and other very small, non-protein molecules.

No, latex is no allergen. And crackers still contain water...

melatonin has very specific shapes, and it binds in a totally different way then an IgX does. Antigenes have not been specifically created to bind to antibodies. However melatonin has..

To develop an allergic reaction in our body some basic fundamental things are needed.

1. The pathogen or foreign peptide as well as allergen have to be foreign and must not be recognized as self tissue.
2. The experience of our immune cells (Adaptive immunity) with the foreign pathogen or peptide. If our immune cells had experienced once then in case of secondary attack the memory B/ T cells will be generated in a large scale to destroy the pathogenic substance.
3. Yes the size matters and when the antigens can't enhance the immunogenicity because of this, then adjuvants are added to the antigen. Adjuvants are substances when mixed with an antigen and injected with it, enhance the immunogenicity of that antigen.

Due to last point the IgE and other antibodies / immunoglobulins will be more effective and can enhance our immunogenicity if administration of an antigen occurs with adjuvants.

But to understand the proteins (antigen) interact with our host immunoglobulins or antibodies, we need to do different immunoassay techniques with ELISA. In ELISA or enzyme immuno assay we used to make a protein protein interaction between the serum or antigen and the high quality antibodies (high quality proteins we buy for) specific to an antigenic protein. If that antigen is present in the serum specific for the antibody we are using, then the Ag-Ab interaction in ELISA plate gives the positive result with color reaction.