In any branch of science there are moments when conventional wisdom is overturned. One of those moments has just occurred in immunology as a result of research at Stanford University. Our previous understanding was too simplistic. Things are even more complicated than we thought.
For years now everyone has believed that lymphocytes can learn to recognise specific molecules but that each type of lymphocyte can only learn a single lesson. One kind of lymphocyte can learn to recognise measles virus, another can learn to spot whooping cough bacterium on sight and another can only be activated by a particular protein made by prawns. Once a lymphocyte has had its initial exposure it will produce memory lymphocytes (CD4 cells) that will hang around for the rest of your life, waiting patiently to deal with a second encounter. This is how adaptive immunity and, of course, vaccination works.
But the one lymphocyte = one lesson theory has just been blown out of the water. It seems that lymphocytes can generalise their learning.
The human brain can generalise easily. Learner drivers are taught to negotiate road junctions. Once the basic skill is there, they will be able tackle all kinds of road junctions. No two junctions are identical but nevertheless the competent driver tackles them all confidently. The learning has been generalised.
Now it seems that memory lymphocytes have some ability to do the same kind of thing. They are even cleverer than we thought. They can recognise not only the microbe that first activated them, but some other types as well.
We knew the immune system was magnificently complicated and now we have to acknowledge the existence of a whole new level of complexity. This new knowledge may shine a light several aspects of how the immune system learns about its environment, such as how benign bacteria help the immune system to develop in childhood.