The Cause of Allegies and Autoimmune Diseases

Keyhole Limpet Hemocyanin (KLH): Internalized Antigen

Scanning the literature for a common protein that can be used as an experimental antigen, it becomes quickly obvious that a favorite is KLH. This would seem to be an odd choice -- why a keyhole limpet protein? But that is the wrong question.

Why is KLH such a good antigen, i.e. why is it readily presented to the host immune system? If you have been reading my posts, you might be thinking about triplets of basic amino acids and that is the answer.

As soon as I remembered the prominent use of KLH as an antigen, I checked the NCBI protein database and immediately found an unusual KKK (triple lysine) near the amino terminus of hemocyanin II ( it comes in two pieces). This triplet explains why KLH is such a good experimental antigen, because it is internalized into antigen presenting cells by its strong heparin-binding domain. Other components, adjuvants, are typically added to the KLH for injection to make sure that a strong local inflammation occurs.

Autoantigens Have Strong Heparin-Binding Triplet

I also learned that Hashimoto’s thyroiditis is an autoimmune disease mediated by the autoantigen thyroid peroxidase. A quick search reveals that thyroid peroxidase is an autoantigen, because it also has a triplet of basic amino acids that can enhance presentation under inflammatory conditions. Grave’s disease of hyperthyroidism is an autoimmune disease in which the thyroid receptor (with a basic triplet) is an autoantigen. The same kind of triplet of basic amino acids was found when I searched today for fire ant antigens and mosquito antigens.

I have also looked for the triplets in protein databases. The triplets are rare in cytoplasmic and extracellular proteins. The proteins that have triplets are usually identified as autoantigens in some disease. The triplets are common in nuclear proteins, since heparin-binding and nucleic acid-binding share the same basic amino acid domains. The nuclear internalization signal also results in rapid cellular internalization, e.g. HIV-TAT, heparanase, IGF-binding proteins. Nuclear proteins are common autoantigens in lupus.

Inflammation Plus Heparin-Binding Internalization: Allergy, Autoimmunity

Chronic inflammation can produce antibodies against proteins (foreign or self) with strong heparin-binding domains (triplets or sometimes neighboring pairs of basic amino acids, lysine or arginine). The generalization explains why particular proteins in pollens, foods, insects, pets, mites, asthma, MS, lupus, celiac, etc. produce antibody responses.

Lactoferrin: Natural Anti-Microbial Milk Protein

Nosocomial infections happen when the immune system is compromised through a medical procedure and common bacteria, such as Staphlococcus aureus, get introduced. From my perspective, that means that the walking bacterial reservoirs, i.e. gut flora of healthcare practitioners, provide an inoculum directly to the damaged tissue, or indirectly by contaminating the patients gut flora and then spreading the pathogens from the patient’s digestive tract to the damage site. This is what happens with ventilator-associated pneumonia and sepsis in critically ill patients.

The trick is to keep the patient’s gut flora healthy -- healthy as a breastfed baby’s. The typical medical approach is to kill off lurking pathogens with a dose of antibiotics. The problem with this approach is that it is both indiscriminant and selective, i.e. it kills both pathogens and beneficial bacteria, but it also provides a selective advantage for the antibiotic resistant hospital strains of opportunistic pathogens.

Humor break: Why do babies spit up half-digested breastmilk and then smile? Answer: Pepsin produces antimicrobial peptides from milk proteins. The baby smugly acknowledges that she knows that she has just protected her upper respiratory and digestive tracts against bacterial pathogens.

Pepsin hydrolyzes proteins next to aromatic amino acids and away from the basic amino acids, arginine and lysine. That means that heparin-binding domains, which consist of groups of basic amino acids in a hydrophobic environment, are clipped out intact from proteins by pepsin. Thus, babies sucking down milk make their own isolated peptides with heparin-binding domains.

Lactoferricin with basic amino acids in blue.

Many organisms, from fruit flies to frogs to humans, produce anti-microbial peptides. They also produce proteins with nucleic acid-binding domains and nuclear localization signals and heparin-binding domains and IP3-binding domains. If all of those binding domains are clipped out by pepsin and the peptides are compared to the anti-microbial defensive peptides, amazingly they are all the same. All have groups of basic amino acids among hydrophobic neighbors, and all are toxic to bacteria.

Lactoferrin is a major component of milk whey. It binds iron and heparin. It can be digested by pepsin into an an anti-microbial peptide, lactoferricin. Baby’s smile and spit-up on your shoes when you say lactoferrin.

Transgenic mice that produce porcine lactoferrin in their milk, transfer extra lactoferrin their little suckling mouse pups and that extra lactoferrin gives extra protection against bacterial and yeast pathogens. That is the experimental justification to suggest that treating patients at risk of nosocomial infections (I guess that would mean every patient in contact with a nurse or doctor) with oral lactoferrin should selectively eliminate the pathogens. Lactoferrin is prebiotic and supports the growth of probiotic gut flora.

ref:
Yen CC, Lin CY, Chong KY, Tsai TC, Shen CJ, Lin MF, Su CY, Chen HL, Chen CM. Lactoferrin as a natural regimen for selective decontamination of the digestive tract: recombinant porcine lactoferrin expressed in the milk of transgenic mice protects neonates from pathogenic challenge in the gastrointestinal tract .J Infect Dis. 2009 Feb 15;199(4):590-8.