Eli Metchnikoff – Cellular and Humoral Immunity, A Historical View

Metchnikoff Von Behring Kitasato: Animal Responses to Infection

Animals survive surrounded, inside and outside, by hordes of primitive microbes. How this is done is a mystery scientists sought to know and discover.

Early experiments in the 1900’s opened the door to the understanding of how animals and humans can exist and thrive in the presence of normal and pathogenic bacteria.

In life, much is assumed. People live, unaware that within them a host of cells and billions of specialized molecules and chemicals keep them alive and well. There is a constant and strong defense against some dangerous, potential foes that can cause disease, the pathogenic microbes. Here see the dawn of insights into host cell and molecular defenses against microbes.

Eli Metchnikoff, Cellular Immune Defense Theory

He was a Russian microscopist, an experimenter, an imaginative and wise scientist. Amidst an odd zoo of sponges, clear starfish larvae and a copepod named Daphnia, Metchnikoff peered into and through their bodies. He described the feeding details and cell responses in his microscopic zoo world.

Metchnikoff soon noted a theme, active microscopic cells within each organism could detect and then eat or completely surround infecting objects such as tiny splinters and ever-present microbes. In Daphnia, he noted an occasional pointed yeast, shaped like a spear at both ends, penetrate the primitive stomach of this flea-like copepod. Ameboid cells immediately surrounded and began to ingest these pointed cells. This is phagocytosis or eating by cells. Human white blood cells (monocytes and neutrophils) eat similarly. These leukocytes (white cells) ingest, then destroy common and uncommon pathogens in our own bodies. Metchnikoff proposed the concept of cellular immune defense as the principal way animals are protected against infectious disease agents.

Emil Von Behring and S. Kitasato, Humoral Immune Defense Theory

The German and the Japanese scientist experimented with rabbits and horses injected with heated cells and broths of diphtheria bacilli, Corynebacterium diphtheriae.

Rabbits injected with the inactive toxin (toxoid) were protected or immunized. Later, when deadly toxigenic C. diphtheriae cells were injected, the immunized thrived and were protected from the toxin of the pathogen. Control, unimmunized rabbits died in a day or two.

Also, when immune serum alone was injected into non-immunized rabbits they were resistant to the virulent bacteria or the toxin. Von Behring and Kitasato proposed the humoral theory of immunity: the acellular, fluid portion of the blood protects against virulent microbes.

Metchnikov versus von Behring and Kitasato

Opposing or conflicting theories are not uncommon in science. Debates, discussion and disagreements may become quite personal. Such was the case with Metchnikoff versus the von Behring and Kitasato team. Each side accused the other of a false or improper theory. Each side held strongly to their viewpoints.

Years passed. The fervor of the debate receded in the face of mounting evidence that showed both sides were right! There were protective phagocytes and there were protective antibodies (humoral factors). Each was important to host survival. Melding of the two views into a new and unified theory settled the issue long after the proponents of the contrasting and apparent divergent views had died.

The Scientific Method Works for All the Sciences

In science, opinions are fine, but solid proof and results are always needed. That is how experimental science works.In the scientific method there is:

  • an observation; e.g. that animals are protected against microbes somhow.
  • hypothesis or speculation as to how this immunity occurs; e.g. It iscellular, or fluid alone.
  • experiment(s); designed and done to test the hypothesis.
  • result(s); analysis, conclusions are made and, if worthy, the results and methods and the whole basics of the process are published for all to see and evalaute.

The work of Metchnikoff and von Behring and Kitasato were each thoughtful and planned well. The results differed because more variables needed to be addressed. Later, other research built on these ideas and showed that yet other kinds of white cells were important.

One can imagine these three meeting to discuss the latest researches in immunity. There they are now- smiling, laughing, shaking hands and noting how remarkable immunity is now and where it was then, and where the world’s understanding will be a decade hence. That seems to be the nature of science and life.

Laughter while learning seems good for the mind and heart.

To those with good scientific minds and a real inclination, education at the college and graduate levels and professional schools is encouraged. Pursue the dream!

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