The Blood System. Serology

The hormone-carrying function of blood was only one of the new virtues of the fluid discovered as the nineteenth century drew to its close. It served as a carrier of antibodies as well, and could thus serve as the general enemy of infection. (It is hard to believe now that a century and a half ago, physicians actually thought that the best way to help a sick patient was to deprive him of some of his blood.)

The use of blood against microorganisms came into its own with the work of two of the assistants of Koch. These were the German bacteriologists, Emil Adolf von Behring (1854-1917)andPaul Ehrlich (1854-1915). Von Behring discovered that it was possible to inject an animal with a particular germ and induce him to form antibodies against it which would be located in the liquid part of the blood ("blood serum"). If a sample of the blood were then taken from the animal, the serum containing the antibody could be injected into another animal, who would then be immune to the disease for a while at least.

It occurred to Von Behring to try this idea on the disease, diphtheria, which attacked children in particular and was almost sure death. If a child survived the disease it was immune thereafter, but why wait for the child to build its own antibodies in a race against the bacterial toxin? Why not prepare the antibodies in an animal first and then inject the antibody serum into the sick child? This was tried during a diphtheria epidemic in 1892 and the treatment was a success.

Ehrlich worked with Von Behring in this experiment and it was probably Ehrlich who worked out the actual dosages and techniques of treatment. The two men quarreled and Ehrlich worked independently thereafter, sharpening the methods of serum utilization to the point where he might be considered the real founder of serology, the study of techniques making use of blood serum. (Where these techniques involve the establishment of an immunity to a disease, the study may be called immunology.)

The Belgian bacteriologist, Jules Jean Baptiste Vincent Bordet (1870-1961), was another important serologist in the early days of that science. In 1898, while working in Paris under Mechnikov, he discovered that if blood serum is heated to 55° C, the antibodies within it remain essentially unaffected, for they will still combine with certain chemicals ("antigens") with which they will also combine before heating. However, the ability of the serum to destroy bacteria is gone. Presumably some very fragile component, or group of components, of the serum must act as a complement for the antibody before the latter can react with bacteria. Bordet called this component "alexin", but Ehrlich named it, straightforwardly, "complement" and it is so known today.

In 1901, Bordet showed that when an antibody reacts with an antigen, complement is used up. This process of "complement fixation" proved important as a diagnostic device for syphilis. This was worked out in 1906 by the German bacteriologist, August von Wassermann (1866-1925), and is still known as the "Wassermann test."

In the Wassermann test, a patient's blood serum is allowed to react with certain antigens. If the antibody to the syphilis microorganism is present in the serum, the reaction takes place and complement is used up. The loss of complement is therefore indicative of syphilis. If complement is not lost, the reaction has not taken place, and syphilis is absent.