In theory there is no limit. Our immune system can “withstand” stresses from countless foreign, non-self molecules (called antigens), and this is because it has the ability to create an extraordinary repertoire of antibodies and T lymphocyte receptors. In fact, thanks to the mechanisms of gene re-arrangement that have developed during the evolution of our species (and, in general, of mammals), theoretically our immune system is able to recognize over 100,000 billion different molecules. So if a person lives 100 years, he could see over 30,000 molecules per second, for a lifetime. It can be easily deduced that a vaccine, which contains a few dozen portions of molecules recognizable by the immune system, does not cause particular stress. As an example, just think that at the moment of birth an individual is almost sterile as he is protected by the maternal environment, but in a few hours he comes into contact with millions of micro-organisms that he is perfectly able to control. And the antigenic load of the first hours of life is much higher than that of the following hundred years.
Send your questions to [email protected]
*Andrea Cossarizza is Full Professor of Pathology and Immunology at the University of Modena and Reggio Emilia