In 1906, a young Viennese pediatrician, Clemens von Pirquet coined the word “allergie” to define the essential features of an immune response, namely, as an “acquired, specific, altered capacity to react”. According to Igea (The history of the idea of allergy.), Von Pirquet’s revolutionary insight was in conceptualizing the function of the immune system as one whose contact with an antigen changes the reactivity of an individual not as one that rids the body of disease.

To appreciate how revolutionary Von Pirquet’s concept was, let’s remember that even today we are taught that the immune system functions to rid the body of disease, particularly disease caused by microbes. Implicit in this definition is the notion that germs cause disease, i.e. Germ theory of disease. Yet today, thanks to exponential technology breakthroughs and large government initiatives like the Human Microbiome Project, we are being forced to confront an essential limitation of the Germ theory based definition of immune system function. The Germ theory is predicated on an adversarial and confrontational approach towards microbes. Then how did we evolve to be multi-cellular organisms that house trillions of microbes? We obviously didn’t evolve multi-cellularity in a vacuum or on a non-microbial planet, and then drop down onto earth to become associated with microbiota de novo. Multicellular evolution and microbiota obviously went hand in hand. How to reconcile our microbiome with the Germ theory based definitions of immune system function. Can we? Should we?

It is one thing to say that germs can and do cause disease, quite another to hold onto a theory that implies that they only cause disease. Maybe it’s time to bring Von Pirquet’s original concept back into play? Let’s think about that for a bit: Per my understanding of Von Pirquet, the immune system does not function to rid the body of disease, rather when the immune system responds, it changes the body’s reactivity. Such a definition does not suggest that the immune system is not capable of ridding the body of disease. It instead suggests that ridding the body of disease is an ancillary, not primary, goal of the immune system. The Von Pirquet definition could be surprisingly a propos: it does not require convoluted posturing to explain how our immune system accommodates our body’s microbiota. With such a definition of immune function, our microbiota could have starring or supporting roles as need be. Our immune system and our microbiota working together could explain some scenarios while their relationship breakdown could explain others. All said, accommodating and working with our microbiota would be a given for an immune system functioning not to rid our body of disease but rather to calibrate in real time our body’s reactivity to its environment. With such a definition, our immune system would navigate our body-microbiota landscape without contradicting the evolutionary dictate.

Post by Tirumalai Kamala:

Towards a germophilic definition of the immune system

Towards a germophilic definition of the immune system