T cells, B cells - antibodies - intervene when viruses and bacteria make us ill and they wipe out intruders effectively but cause collateral damage in the body's own tissue, which has to be repaired.

In order for our immune system to not be in a constant state of 'red alert', causing chronic inflammation, there is a second defense system switched in series between our bodies and the outside world, essential because because there are trillions of bacteria on the barrier tissue like our lungs and skin. The majority of these microorganisms have been living with our body's cells as good neighbors for millions of years and the complex symbiosis of very different microorganisms supplies us with important natural substances such as vitamin B12.

I've lamented multiple times the negative influence on scientific culture of some trends in the use of computational tools to analyze large datasets, particularly in biology.

Over at Nobel Intent, John Timmer brings up another issue related to computational models of complex phenomena: reproducibility: