Human beings have co-evolved with a myriad of pathogens. Gladly. We co-exist and live with thousands of species of viruses, bacteria, fungi. Many viruses embed and dis-embed their genetic material into ours in a natural way. In fact, our own DNA contains ancient viral sequences of genetic material which we will pass on to the next generation. More than 100.000 trillion microorganisms inhabit our guts and influence our lives, for the better. The air around us has quadrillions of bacteria and viruses: millions of them floating in each cubic meter. We breathe in a few hundred thousand viruses every minute. Most of them are neutral to us, but part of them are human pathogens: they can cause infections to humans. And yet, we get such infections very rarely. Say thanks to the immune system: the human immune cells can identify pathogens and neutralize them, either by direct attack or by synthesizing antibodies complementary to each available pathogen particles (antigens); and there are more than one quintillion unique types of antibodies.
The immune system’s function is due to its unique genetic/molecular machinery, capable of taking advantage of genetic rearrangements. But this is not enough; its function is also dependent on the interactions between our body and microorganisms. This can be proven in at least two ways….