Allergy questions

[mith]

The digestion of proteins should begin in stomach(3-6 hours) and end in intestines(another 3-6 hours). If it's not digested then it's passed out. If it is an allergic reaction there should be a response as soon as it gets into the bloodstream.

[aharown07]

The digestion of proteins should begin in stomach(3-6 hours) and end in intestines(another 3-6 hours). If it's not digested then it's passed out. If it is an allergic reaction there should be a response as soon as it gets into the bloodstream.

OK... but it's my impression that digestion involves extracting proteins from the food (along w/dissoving sugars and starches).. but what does it do (if anything) to the proteins?
I believe I've read that at least some of them are needed "intact" in the bloodstream. I just don't know how common that is, or how fast they are usually consumed by cells once in the bloodstream... could proteins of a particular sort (milk proteins for example) accumulate there over time?

[aharown07]

I gather that at least some proteins are denatured (which I think means the folds of the protein are altered while the peptide structure remains intact?) in the stomach via enzymes... maybe some of them actually coming apart, so to speak, at that point.
But I have no idea what happens to them after that.

[mith]

No, digestion is chemical breaking down of food. Stomach churning will effectively expose all proteins to proteases and acid. Those not cleaved in stomach are cleaved in duodenum. Then it's off to the rectum, I don't see where you could "store" the proteins.

Unless your proteins are coated like asprin tablets/fish oil capsules, they would become processed in teh stomach. http://www.drugdeliverytech.com/cgi-bin ... rticle=162

[aharown07]

No, digestion is chemical breaking down of food. Stomach churning will effectively expose all proteins to proteases and acid. Those not cleaved in stomach are cleaved in duodenum. Then it's off to the rectum, I don't see where you could "store" the proteins.

Unless your proteins are coated like asprin tablets/fish oil capsules, they would become processed in teh stomach. http://www.drugdeliverytech.com/cgi-bin ... rticle=162

Along those lines, I just read something similar...
"Complex carbohydrates are broken down into simple sugars (mainly glucose) by the enzymes amylase, lactase, sucrase and maltase. Fats are broken down to fatty acids and glycerol by lipase enzymes, and protein is degraded to amino acids by pepsin, trypsin and chymotrypsin."

But if this is the case, how can an ingested protein ever trigger an allergic reaction? One would never reach the bloodstream.

I must be missing something pretty big here.

[aharown07]

I think I may have found the answer.
http://www.emedicine.com/ped/topic1908.htm

Here's an excerpt

Pathophysiology: The major food allergens are water-soluble glycoproteins (molecular weight [MW] 10,000-60,000) that are resistant to heat, acid, and enzymes. The gastrointestinal tract is permeable to intact antigens. The antigen uptake is an endocytotic process involving intracellular lysosomes. Some antigens can move through intercellular gaps; however, the penetration of antigens through the mucosal barrier is not usually associated with clinical symptoms. Under normal circumstances, food antigen exposure via the gastrointestinal tract results in a local immunoglobulin A (IgA) response and in an activation of suppressor CD8+ lymphocytes that reside in the gut-associated lymphoid tissue (oral tolerance).

In some children who are genetically susceptible, or for other as-yet-unknown reasons, oral tolerance does not develop and different immunologic and inflammatory mechanisms can be elicited. Whether nonimmunologic mechanisms can have a role in the development of specific intolerances to food proteins is still disputed. ...

So.... what I think they're saying is that some proteins (glycoproteins?) don't get dissolved by protease, etc., but rather, pass through the intestinal wall and then may become allergens in some people.

I'm guessing nobody knows for sure how long these glycoproteins might last (and/or accumulate) in the bloodstream? Seems that immune system will go after them pretty quickly and either dispose of them "normally" or in some dysfunctional "allergic" way?

[mith]

Assume you have an allergen protein that is small enough to be absorbed and you lack an enzyme to cleave it, and it is somehow stable enough to withstand all other digestive means.

If it goes into your bloodstream and interacts with mast cells to produce histamine, you'll have your reaction. Antibodies may be produced to neutralize it. You might have some macrophages eat it or whatever.

But I don't think there's any sort of latency period for allergies.