In 1888, Dr. Paul Ehrlich, who worked in Robert Koch’s laboratory in Berlin, was in Egypt when he treated a boy who had been bitten by a snake. The boy’s father told Ehrlich that he himself had survived several snakebites and that the symptoms had become milder each time he was bitten. Ehrlich realized that the man had developed a lasting immune response to the venom: an antivenin.

On his return, Ehrlich met the biologist Emil von Behring, who was conducting experiments in which he used the serum of an animal infected with tetanus or diphtheria to confer immunity on another animal. Ehrlich speculated that when a toxin bound itself to a cell, the cell produced more of the antibody (a word Ehrlich coined) to defend itself. With repeated exposures the antibody was secreted into the blood, creating lasting immunity. The substance that created the antibody was known as the antigen.

It was almost seventy years before an Australian immunologist called Frank Macfarlane Burnet realized how antibodies were created. Ehrlich, and other scientists such as the Nobel laureate Linus Pauling, had thought that antigens contained instructions to create specific antibodies. Burnet proposed that the cells that bind to antibodies contain only one receptor for an antigen, meaning that the cell, not the antibody, is selected and grows when bound to the antigen. As the author remarks: “Proteins don’t grow on command, but cells do.”

The chapter concludes with an account of the ongoing attempts to make antibodies into drugs. In particular, Ron Levy, an immunologist at Stanford University, has attempted to use cancer cells fused with plasma cells to create enduring antibodies, resulting in the development of the drug Rituxan.