When an animal is infected, either naturally or by experimental injection, with a bacterium, virus, or other foreign body, the animal recognises this as an invader and acts in such a way as to remove or destroy it.

I wasn't a particularly brilliant student, but on the other hand, I was very active in Student Union affairs and in student politics.

Back in 1962, when I had by accident become the supervisor of Roberto Celis in Argentina, it occurred to me that antibody diversity might arise from the joining by disulphide bridges of a variety of small polypeptides in combinatorial patterns.

As we returned to Argentina, I started seriously to work towards a doctoral degree under the direction of Professor Stoppani, the Professor of Biochemistry at the Medical School.

The study of the amino acid sequence around the disulphide bonds of the immunoglobulins was my own short-cut to the understanding of antibody diversity.

What attracted me to immunology was that the whole thing seemed to revolve around a very simple experiment: take two different antibody molecules and compare their primary sequences.