The early work on the organism and the toxoid vaccine reads like the ‘Who Is Who’ of microbiology: Klebs, Loeffler, Koch, Roux, Yersin, Behring, Kitasato, Schick, and T. Smith were all involved in bringing this deadly disease under control.
In those days bacteria and diseases were referred to by the names of researchers, discoverers, and clinicians. Corynebacterium diphtheriae was referred to as the Klebs-Loeffler bacillus. TB was known as Morbus Koch and leprosy as Morbus Hansen. This tradition has been fading into oblivion esp. as the etiology has become clearer, but we still call Crohn’s disease, Sjogren’s syndrome and Behcet’s by their eponyms. Other names have become obsolete; few would nowadays associate Morbus Boeck with sarcoidosis or Morbus Bechterev with ankylosing spondylitis.
After Klebs discovered the diphtheria bacillus, Loeffler developed a specific growth medium now called Loeffler medium and recognized that it was this particular bacillus that causes diphtheria. He also made some very astute observations: having found the organism only in the diphtheric membranes but nowhere else in the bodies of infected children, he suggested the systemic disease manifestations were being caused by a bacterial product, the toxin later identified by Behring and his coworkers.
As vividly described by Paul de Kruif, Behring had to kill a lot of guinea pigs in his lab to prove that protection against the diphtheria toxin can be generated and a toxoid preparation can induce long-lasting immunity in humans.[1] De Kruif’s book chapter on Roux and Behring has the subtitle “Massacre the Guinea Pigs” describing the travails of researchers introducing a new treatment, in this case an inactivated vaccine for a deadly disease.
In those days there was no FDA, CDC, GCP, or ICH, no governmental oversight over human testing. None of these gentlemen had training in research ethics. Diphtheria antitoxin was first given to a child in 1891, equivalent to a 2-3 year development timeline!
The vaccine made a huge impact on morbidity and mortality worldwide.
Diphtheria research is not finished. We know a lot about the toxin’s structure and MoA. It is an A/B type peptide consisting of 2 chains: B for cellular binding and A for disruption of intracellular protein synthesis. Peptide A binds to EF2, blocks its action,
and leads to cell death. This is an abbreviated explanation for a very unusual interaction between DT and a post-translationally modified histidine on EF2 called diphthamide. It is the A-toxin of C. diphtheriae that modifies diphthamide on EF2 by ADP-ribosylation. This inactivates EF2, blocks protein synthesis and leads to cell death.[2]
Clinicians wondered early on why the diphtheria toxin has such a profound effect on the heart.[3] Effects on the vagus nerve, conduction system, and myocardial cells in general were considered. The most common findings of conduction abnormalities were documented in many cases (as in the ECG below) and histopathology pointed towards a toxic myocarditis.
We did not find studies that would explain the particular sensitivity of the heart for EF2 blockade by diphtheria toxin. If any of you have an explanation, please share it with our readers.
Last, a bit of trivia:
Friedrich Loeffler, was a German microbiologist and a “microbe hunter whose mustache was so militaristic he had to keep pulling it down to see through the microscope”.[1] Indeed, he had an impressive beard!
In contrast, Wilhelm Löffler (note the different spelling!) was a Swiss clinician known for studies on eosinophilic myocarditis and tropical eosinophilic pneumonia.[4] Pictures show him with a moustache but never a full beard, making it easy not to confound him with his namesake. We do not know whether his moustache got in the way when studying eosinophils under the microscope.
ABBREVIATIONS
DT diphtheria toxin
EF2 elongation factor 2
REFERENCES
[1] De Kruif, P. Microbe Hunters. 1926
[2] Su, X. The biosynthesis and biological function of diphthamide. Crit Rev Biochem Mol Biol, 2013; 48: 515, 2013
[3] Marvin H. The effect of diphtheria on the cardiovascular system. Am J Dis Children. 29: 433, 1925
[4] Löffler, W. Endocarditis parietalis fibroplastica mit Bluteosinophilie. Ein eigenartiges Krankheitsbild. Schweizerische Medizinische Wochenschrift 66: 817, 1936
