Thinking about the Creation of Antibodies

Drawings of the interaction between an antibody and azoprotein by Linus Pauling. 1940s.

[Part 1 of 3]

During a period of about a decade, beginning in 1936, my principal research effort was an attack on the problem of the nature of life, which was, I think, successful, in that the experimental studies carried out by my students and me provided very strong evidence that the astonishing specificity characteristics of living organisms…is the result of a special interaction between molecules…

-Linus Pauling, 1991

As one would expect, the Great Depression made it extremely difficult to acquire funding for scientific research. Luckily for Linus Pauling, he had on his side the patronage of the Rockefeller Foundation, and a close friendship with Warren Weaver, the head of the foundation’s Physical Sciences Division. Weaver wanted Pauling to get more involved in biological research, specifically protein research. Pauling was hesitant, but Weaver controlled the funding and convinced Pauling to move forward.

Alfred Mirsky

By 1933 Pauling was heavily involved in research on proteins, specifically their shape and function. In 1935 he began working with Alfred Mirsky, a Rockefeller Foundation scientist, with whom Pauling concluded that all proteins are structured as chains, and that the shape of a given protein determines its function and behavior.

A large component of Pauling and Mirsky’s research was on protein denaturation, effectively the breakdown or death of proteins. It was known that modest heating, mild acids, milk alkalis, or agitation, such as beating eggs with a fork, all serve to denature a protein. However, Mirsky discovered that proteins that were slowly denatured at lower temperatures could be resuscitated and the process reversed.

Karl Landsteiner

In the Spring of 1936, Pauling began another collaboration, this time with Karl Landsteiner, an Austrian scientist who won a Nobel prize for discovering and developing the field of blood typing. Landsteiner invented the ABO system, and uncovered methods for making blood transfusions safe. In this research Landsteiner observed that, in instances where the wrong blood type is used in a transfusion, antibodies attacked the transfused blood. Pauling was intrigued by Landsteiner’s work, and began reading about antibodies; he was interested and puzzled by what he found. While the scientific community knew that antibodies worked, how exactly they worked and how exactly they were formed were still unknown.

At the time, there were four main schools of thought regarding the creation of antibodies: the Antigen-Incorporation theory, the Side-Chain theory, the Instruction theory, and the Selection theory.

The Antigen-Incorporation theory, originally proposed by Hans Buchner in 1893, proposed that antibodies were actually the byproduct of antigens “splintering” in the human body and becoming incorporated into it. Despite the fact that this theory had been largely disproven at the time, it was proposed again by E. Hertzfeld and R. Klinger in 1918, by W.H. Manwaring in 1926, by Locke, Main, and Hirsch also in 1926, and finally once more by Gustave Ramon in 1930.

The Side-Chain theory was posited by the famous Paul Ehrlich in 1897, who argued that the body’s immunological reaction to antigens was “only a repetition of the processes of normal metabolism.” Ehrlich thought that cells would digest certain antigens in the same way that they digested nutrients. After repeated assimilations, or too large of an assimilation, the cells would overcompensate and release antibodies. His theory included a number of issues that the scientific community could not solve at the time, and it took over sixty years for the model to be improved upon.

The Instruction theory states that the body uses antigens as a template, then manufactures antibodies to specifically combat the antigen that the antibody is based off of. Pauling eventually belonged to this school of thought, as did Landsteiner, Michael Heidelberger, Felix Haurowitz, and Jerome Alexander. This group was far from unified however; the only point on which adherents to this school agreed was that antigens acted as templates. How antibodies worked, and how they were produced, was still a highly contentious question.

The final theory was the Selection theory, which was in concept almost identical to Ehrlich’s Side-Chain theory, except that its explanations were based on more modern mechanisms. Instead of general metabolic processes, quantum mechanical forces were proposed to be the cause of the attraction between antigens and antibodies. This school of thought became more popular near the end of World War II and in the post-war era.

Pauling described Antibodies as “fantastically precise little weapons,” and found it fascinating that they could identify and attack invading molecules that were different from safe molecules by only a few atoms. Antibodies are made of pure protein, are remarkably similar to one another, are relatively enormous, and also attack vastly different types of molecules.

Pauling and Landsteiner were especially vexed by how antibodies could target varied molecules so precisely when they were so similar. Pauling proceeded to read Landsteiner’s book on antibodies, and began to wonder if shape affected antibodies as much as it affected regular proteins. Landsteiner had arrived at a similar conclusion, and in 1939 published a note in Science suggesting that shape was what determined the effect of antibodies.

Diagram included in Pauling’s article, “A theory of the structure and process of formation of antibodies.” 1940.

Pauling expanded upon this idea, and in 1940 published a paper in which he hypothesized that antibodies were built as chains of non-specific proteins which collided with antigens, then compressed and shaped themselves around the antigen, “like wet clay pressed against a coin.” The paper created quite a stir, and generated a lot of support for the notion of using chemistry to solve biological questions. Unfortunately for Pauling, it later turned out that his hypothesis was deeply flawed.

Another argument developed in the 1940 paper was that antibodies are bivalent – that is, they have two sites which can bind to antigens. In addition to being bivalent, Pauling hypothesized that each of the “arms” of an antibody could latch onto different kinds of antigens. While Pauling was incorrect on the latter part – antibodies can only grab onto one type of antigen – he was correct that they are bivalent.

Pauling had gotten off to a strong and noticeable start in the field of immunology. Whether correct or incorrect, he was making progress towards a greater understanding of how the body protects itself. As the clouds of war began to reach across the Atlantic and Pacific towards the United States, Pauling’s new and growing knowledge was going to be put to the test.

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