Campbell, Pressman, Pauling and the Binding of Antibodies

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

Dan Campbell first collaborated with Linus Pauling on a fellowship at Caltech in 1940, during which time the duo tried to explain how antibodies are formed. At the time, Pauling believed that antibodies were proteins in-the-making that needed to bind to antigens in order to fold and complete their structure. If this principle was correct, Pauling thought, it might be possible to create artificial antibodies by simply denaturing proteins and allowing them to bind and refold in the presence of antigens.

Despite the fact that Campbell’s initial test results cast doubt on his collaborator’s theories, Pauling went ahead and published his ideas on how antibodies work, hoping that further research could support his paper. Thus began a lengthy study of antigen-antibody binding in which Pauling and Campbell attempted to develop a complete theory. Along the way, Dan Campbell’s research at Caltech would become very important to the Institute as well as to Pauling.

In 1943 a Caltech research fellow named David Pressman agreed to join Campbell and Pauling in their study of immunology. Starting with work that had previously been published, Pressman, Pauling and Campbell refocused their studies to explain how antigens and antibodies bind, a change in focus from Campbell and Pauling’s earlier inquiries into how antibodies and antigens are formed. The decision to focus on previous research was made after Pauling had mistakenly announced that antibodies had successfully been synthesized at the Gates and Crellin Laboratories. As it turned out, attempts to create synthetic antibodies using Pauling’s proposed methods were completely unsuccessful. Pauling thus decided to start from scratch by developing a theory of antigen-antibody binding, which he would use to further investigate the chemistry of this interaction.

In July 1943, the three men published “The Nature of the Forces Between Antigen and Antibody and of the Precipitation Reaction,” appearing in the journal Physiological Reviews. The paper attempted to make more educated predictions about antigen-antibody binding.  In doing so, the article begins by referencing the concept of structural complementarity, which posits that antigen-antibody binding is driven by the close complementary physical shapes of the two molecules, which fit together like two adjoining pieces in a jigsaw puzzle. Commonly referred to as “the lock and key mechanism,” this idea was developed in the early 1930s, and served as Pauling and Campbell’s starting point in their initial investigations.

The 1943 study also drew from outside theories, such as the framework theory of precipitation, to suggest that antigen-antibody binding results in the formation of a precipitate; that is, that the two structures react to form an insoluble compound. Using these points as their foundation, the three researchers developed a new theory of antigen-antibody binding.

Pauling and Campbell, 1943.

Pauling and Campbell, 1943.

Campbell, Pressman and Pauling’s breakthrough came by way of their proposal that structural complementarity is an especially important feature for reactions that depend on Van der Waals forces. Van der Waals forces are weak forces of attraction that bind together molecules located in close proximity to one another. The Caltech researchers believed that the close complementary geometry of antibodies and antigens was significant enough to enable these molecules to fit together using the weak Van der Waals attraction as a binding force. In other words, the summation of Van der Waals forces present along the binding site of an antibody worked to bind it to its antigen, specifically because the shapes of antibodies and antigens complimented each other so closely. This theory explained much of what had been observed by immunologists across the discipline in multiple investigations of antigen-antibody reactions.

From here, the three researchers also asserted that two propositions placed forth in Pauling’s 1940 paper should still be considered for further study: the multivalence of antigen-antibody interactions and the probability of hydrogen bonds acting between the two molecules. The trio also concluded that the antigen-antibody mechanism would require at least two supplementary types of forces: Coulomb attraction and polar attraction.

Of the conclusions published by Campbell, Pressman and Pauling in 1943, the multivalence of antigen-antibody interactions and the three proposed forces (Van der Waals, Coulomb and polar) between the two molecules are still considered to be contributing factors to the functioning of the human immune system. With this publication, Campbell, Pauling and Pressman also showed that the immune system relies heavily on both structural and chemical features to carry out its processes.

The important conclusions derived from research conducted by Campbell, Pauling and others established Caltech as a leader in the field of immunology. Over the years that followed, Campbell and Pauling continued to develop their theory of antibody formation, which remained widely accepted until the 1950s. Even when the duo’s work began to be disproven by findings in the genetics field, the understanding of antigen-antibody interactions suggested by research done at Caltech remained undisputed.

Dan Campbell and Linus Pauling went on to publish more than twenty articles relating to immunology, exchanging ideas on the topic until the end of Pauling’s tenure at Caltech in the early 1960s. The attention that their work brought to the Gates and Crellin Laboratories at Caltech prompted the creation of a separate department, one that was entirely dedicated to immunochemistry. (The first of its kind on the west coast.)

For thirty years, Campbell headed Caltech’s immunochemical research and his fame as an immunologist grew to the point where, in 1972, he was named president of the American Association of Immunologists. Two years later, in 1974, Campbell passed away at the age of 67, the victim of a heart attack.  Over the course of his career, he published more than 200 papers as well as several books, and he served on editorial boards of four scientific journals related to immunology.


The Arrival of Dan Campbell at Caltech

Dan Campbell, ca. 1940s.

Dan Campbell, ca. 1940s.

[Part 1 of 2]

As a scientist, Linus Pauling is remembered by many for combining his expertise in chemistry with other fields. Often times Pauling would start off thinking about a problem from a chemical perspective and end up learning about a field entirely new to him, like cellular biology or medicine. Though this sort of cross-disciplinary work is more commonplace today (partly because of the example that Pauling provided), in the 1930s it was fairly rare for scientists to combine different fields of study. This given, pioneers of the cross-disciplinary approach often found it difficult to identify like-minded researchers with whom to collaborate. Fortunately for Pauling, a man with a very wide network, other researchers often found him.

After delivering a talk about hemoglobin in 1936, Pauling was pleasantly surprised to be consulted by Austrian medical researcher Karl Landsteiner. For many years, Landsteiner had been trying to understand how antibodies in the immune system work, and he believed that Pauling’s knowledge of medicine and chemistry could help him in his investigations. An antibody is a disease-fighting macromolecule that targets and rids the body of unwanted foreign substances, such as viruses and incompatible blood types. Landsteiner wanted to know how antibodies can target specific foreign substances with such precision. This encounter drew Pauling’s attention to the field of immunology, which would eventually become an important part of his research and would remain so for many years to come.

Pauling’s communications with Landsteiner spurred an interest in looking into the chemistry of antibodies and their substrates, antigens. At the time, however, most of Pauling’s focus was necessarily occupied with finishing up his previous program of grant-funded research on protein structures. Furthermore, Pauling was not an immunologist and the demands on his time were such that he could do little more than keep immunology in the back of his mind.

It wasn’t until 1939 that Landsteiner once again brought Pauling’s full attention back to antigens when he used Pauling’s theory of protein structure in a discussion about antibodies. Reading Landsteiner’s article sparked several ideas for Pauling which quickly led to his drafting a rudimentary theory of antibody chemistry. Six months later he found the perfect opportunity to test some these ideas.

Image extracted from a glass plate display, “Pictures of Antibodies,” prepared for the First International Poliomyelitis Conference, New York, 1948. The caption accompanying this image reads: “…[An] antibody-antigen framework which may precipitate from a solution or be taken up by phagocytic cells.”

In January 1940, immunologist Dan Campbell first visited Caltech on a fellowship. Campbell was an Ohio native who had been trained at Wabash College in Indiana and George Washington University in St. Louis, before receiving a doctoral degree from the University of Chicago, where he was subsequently hired as an assistant professor. During his tenure at Chicago, Pauling invited Campbell to spend a fellowship period at Caltech.  Campbell was only scantly familiar with the Institute, but was aware of the reputation of its chemistry department and accepted Pauling’s offer largely on this basis.

Due to his unfamiliarity with the institution, by the time of his arrival in Pasadena Campbell had still not yet identified a research project on which to collaborate. Pauling advised Campbell to consider different researchers before making his final decision on where and with whom he might work. In the end, after asking around, Campbell chose to collaborate with Pauling on his theory of immunology.

This was a fortuitous decision, for several reasons.  First, in addition to immunology, Campbell had a background in biophysics and chemistry, which made him a perfect candidate to test and develop Pauling’s antigen theory. More importantly, as Campbell began his initial investigations, it became apparent that Pauling’s ideas were flawed and that Pauling’s knowledge of chemistry alone would not be sufficient to make further progress in immunological research.

Campbell and Pauling, 1943.

Pauling had alleged that antibodies were similar to denatured proteins; that is, a protein that has lost its secondary and tertiary structures and has unfolded into an amino acid chain. Pauling’s theory anticipated that antibodies were an unfinished protein that required specific antigens in order to fold into the proper secondary and tertiary structures.

According to this model, antibodies would only form hydrogen bonds and thus would coil around chemically complementary antigens. As such, the theory explained how antibodies are able to bind unambiguously to their complementary molecules. However, Campbell’s results did not support all of Pauling’s ideas. Though his research showed that antibodies were in fact proteins, their physical structure before and after binding to antigens remained unclear.

Pauling’s lack of evidence for his theory of antibody structure and composition limited him to publishing only a single theoretical paper in which he explained his ideas about antibodies. In July 1940 the Journal of the American Chemical Society featured Pauling’s “A Theory of the Structure and Process of Formation of Antibodies.” The article received much attention and, despite the lack of evidence, was widely acclaimed, though it failed to provide a definitive explanation for antibody structure.

After the publication of the piece, Campbell once again tested Pauling’s theory, and this time his results were much more confusing, to say the least. Initially, it appeared that Campbell had succeeded in creating artificial antibodies by simply denaturing beef globulins (a protein found in blood) and later allowing them to refold around an antigen.

Word of these results greatly excited Pauling, who began to envision the mass production of antibodies using Campbell’s method. Reality turned out to be not so simple; when students and postdoctoral fellows tried to replicate Campbell’s experiment, they were unable to obtain the same results. Looking back now, it seems most likely that Campbell’s research assistants had misinterpreted the results of his experiment.

Pauling knew that he would need more time with Campbell to refine his theory, but that could only happen if Campbell’s position at Caltech was secured. In 1942 Pauling arranged for the Institute to offer Campbell an assistant professorship, which he accepted. By 1950 Campbell had become a full professor.

Combining immunology and chemistry proved to be a commendable approach for tackling many health concerns of the time. Likewise, Campbell’s presence was crucial to the development of Caltech’s immunochemistry department, which over a span of five years grew from a single office (Campbell’s) to a space occupying most of the third floor of Caltech’s Church Laboratory. Students and professors alike flocked to the growing department to discuss questions and engage in research on immunology, using chemistry as the basis of their approach. From the outset, both Pauling and Campbell benefited from one another’s expertise while colleagues at Caltech, and their partnership would continue to yield fruit for many years.

On the Formation of Antibodies

By the 1940s, Linus Pauling’s research interests had expanded to include many subjects generally outside the purview of a typical chemist. In particular, immunology was rapidly becoming a fascination of his – one that would come to devour more and more of his time both in and out of the lab. For Pauling, much of the human body could be viewed as a gigantic set of very complicated chemistry problems, and he derived great joy from being able to solve some of these problems. Among his most important immunological discoveries were his elucidation of the role that hemoglobin plays in sickle cell anemia and his theory of antibody formation.  The latter is the topic of today’s post.

In 1940 Pauling published a paper – now his ninth most cited – in the Journal of the American Chemical Society on the subject of antibodies and antigens. This manuscript, titled “A Theory of the Structure and Process of Formation of Antibodies” is fundamentally based around one important assumption that Pauling made about antibody structure, “…that all antibody molecules contain the same polypeptide chains as normal globulin, and differ only in the configuration of the chain; that is, in the way that the chain is coiled in the molecule.”

Antibodies are protein molecules that play an extremely important role in the human body. Their main function is to identify and neutralize foreign objects, called antigens, that have been taken up by the body. Antigens come in many varieties, including high-molecular-weight carbohydrates, lipids, pollen and bacterial cells. It is important to note too that only antigens marked by the body’s systems as “foreign” will set off an antibody response; antigens marked as “self” are tolerated by the body.

Pauling with Dan Campbell, a primary colleague in Pauling's antibody work.

Antigens play an important role in Pauling’s theory, which argues that antigens alone determine the configuration of a specific portion of the antibody molecule. For example, without the presence of an antigen, a normal globulin protein will be synthesized. In the presence of an antigen however, a specific antibody will be produced, a portion of which will be complementary in structure to the antigen that in question. In describing this process, Pauling’s paper first details the four steps that occur in the formation of a normal globulin molecule, which are summarized below.

  1. The polypeptide chain is synthesized. The two ends of the chain are free, but the center of the chain is still attached at the site of synthesis.
  2. The ends coil into either their most stable, or another very stable, configuration. Hydrogen bonds and other weak forces between amino acids in the polypeptide chain stabilize the two ends.
  3. The center of the chain is freed from the site of synthesis.
  4. The center coils into its most stable configuration, and the globulin molecule is completed.

Because antibodies are simply modified globulin molecules, the process for their formation is closely related to that of globulin. Summarized below then, are Pauling’s six steps of antibody formation.

  1. An antigen is held in place at the site of antibody production and the antibody is synthesized around the antigen molecule.
  2. The ends of the newly synthesized antibody coil into a configuration complementary to groups on the antigen and attach to these complementary groups.
  3. The center of the chain is freed from the site of synthesis, causing one of two things to happen. If the forces between the ends of the chain are sufficiently strong, both ends will continue to be attached to the antigen, and the antibody will never be completed.
  4. If they forces between the ends of the chain and the antigen are weak, one end will dissociate from the antigen.
  5. Assuming one end of the chain dissociates from the antigen, the center of the chain coils into its most stable configuration, making a complete antibody.
  6. Eventually, the antibody will dissociate from the antigen and float away.

To summarize, Pauling’s theory of antibody formation argues that every antibody has the same configuration in the center of its polypeptide chain, and that the configuration of the ends of the chain are dependent on which antigen is present at the time of the antibody’s synthesis.  In present day, even with our better understanding of antibody synthesis, the core principles of Pauling’s theory – most prominently the idea that each antibody shares a common structure – remain sound.

The entirety of Pauling’s manuscript is available here.  In it, he discusses other topics related to his theory, including the formation of different structures based on antibody to antigen ratios, the characteristics that define a molecule or substance as an antigen, and the compatibility of his theory with experimental results. For more information on Pauling’s immunological work, visit It’s in the Blood: A Documentary History of Linus Pauling, Hemoglobin, and Sickle Cell Anemia.

Thinking Between Disciplines: Immunological Interests and Beyond

I believe that chemistry will play a very important part in the golden age of biology that is now beginning.”
– Linus Pauling, “Molecular Structure and Biological Specificity,” July 17, 1947.

One of the reasons why Linus Pauling enjoyed such a prolific and diverse scientific career was his ability to combine and draw inspiration from rather disparate interests and research questions.

Indeed, structural chemistry – the discipline with which Pauling is most commonly associated – appealed to Pauling in part because it allowed him to consider the physical causes underlying the chemical nature of certain biological phenomena in concert with known principles of chemical interaction.  In other words, Pauling viewed structural chemistry as the avenue by which he could best utilize the tools not only of chemistry, but of physics and biology as well.

Many of Pauling’s laboratory experiments rested on knowledge and methods borrowed liberally from biology, medicine, chemistry and physics. In a 1946 proposal for a program of fundamental research in biology and medicine at Caltech, Pauling emphasized that the long-established cooperation of the Institute’s divisions of Biology, Chemistry, and Chemical Engineering were resulting in a vigorous and successful “attack” on the “great fundamental problems of biology and medicine.” As he sought to justify the expansion of these interacting programs, Pauling wrote that the “primary features” of their organization were “the presence of a group of men rigorously trained in the exact sciences and interested in attacking…broad problems.”

Of nearly-equal importance was an “unusual spirit of cooperation.” Such ‘unusual cooperation,’ in Pauling’s opinion, could be expected to produce work that was at once “sound but imaginative,” and indebted to “the transfer of ideas among different fields…ranging from quantum mechanics to animal physiology.” Pauling’s ideas on the nature of hemoglobin and sickle cell anemia were two of the ‘sound but imaginative’ ideas that arose out of the broader culture of interdisciplinary laboratory research.

In the 1930s Pauling came under the influence of a prominent immunologist, Karl Landsteiner, who helped to turn his attention and interest towards the mechanism of immunological response. To Pauling, the fundamentals of immune response in the body seemed reminiscent of the folding of hemoglobin in the presence of iron. Both mechanisms underscored the importance of the physical structure of a molecule in influencing its chemical interactions.

Pauling’s work on both the nature of hemoglobin as well as the immunological reaction to antigens and foreign proteins were linked practically, as well as conceptually, to his hemoglobin research. As he came to learn more about immune response, Pauling applied some of this knowledge to increasing the practical value of his work on the development of Oxypolygelatin, a blood substitute created as part of the Pauling’s contributions to the Allied effort during World War II.

An original container of 5% Oxypolygelatin in normal saline. Developed by Linus Pauling as part of his scientific war work research program, mid-1940s.

An original container of 5% Oxypolygelatin in normal saline. Developed by Linus Pauling as part of his scientific war work research program, mid-1940s.

This project, which was not completed to fruition until 1949, was vexed by certain problems having much to do with the nature of blood in the human body. In a handwritten note from 1945, Pauling suggested that foremost among his concerns vis-a-vis the creation of a suitable blood alternative were both a “lack of toxicity,” and a lack of “antigenicity.”

Pauling’s ideas on the nature of hemoglobin, sickle cell anemia and the blood substitute Oxypolygelatin were all born of his ability to fruitfully-combine the methods of several different disciplines with the expertise of his colleagues and fellow researchers. Even moreso, this remarkable body of work constitutes a clear example of the important place that interdisciplinarity can assume in scientific research.

To learn more about Pauling’s research on hemoglobin, immunology and Oxypolygelatin, please visit the website It’s in the Blood!  A Documentary History of Linus Pauling, Hemoglobin and Sickle Cell Anemia.