Original (antigenic) sin

(First of two parts)

No! This is not about what that Couple did in the Garden, which many believe is the cause of all the misery that we are now suffering on Earth. This is about what our immune system does when responding to attack by certain pathogens that are causing us a lot of misery.

When a pathogen manages to enter our body, our immune system tries vigorously to get rid of it. One of the actions of the immune system is to produce antibodies that would bind to the pathogen (and any toxin it may produce), prevent it from entering its target cell, or otherwise cause its demise. The antibodies bind specifically to the antigens of the pathogen (or to its toxins). Now, antibodies can be produced against essentially any exposed part of an antigen, but some parts attract a greater antibody response than others; those are the so-called “immunodominant epitopes.”

It takes a few days for our immune system to mount an effective response to invasion by a pathogen that it has never seen before. (In the meantime, we are sick.) If we survive those few days, our immune system will not only get rid of the pathogen, but will also be ready to meet another invasion by the same pathogen. (Our immune system has memory.)

But some pathogens are very clever. They mutate. When that happens, the antibodies and the other components of the immune system that were generated to specifically counter a particular pathogen, will no longer work — not very well, anyway. (We get sick again.) And often it’s because of “original antigenic sin.”

(The Doctrine of the Original Antigenic Sin was proposed by Thomas Francis Jr. and colleagues about 50 years ago to explain the persistence of the antibodies, which had been produced against the particular strain of a pathogen encountered early in life, even after later exposure to other strains of the same pathogen.)

(To be concluded)

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Eduardo A. Padlan is a corresponding member of the NAST and is an adjunct professor in the Marine Science Institute, College of Science, University of the Philippines Diliman. He can be reached at [email protected].