What You Will Learn in This Article

The 1908 Nobel Prize in Physiology or Medicine was jointly awarded to Paul Ehrlich of Germany and Ilya Mechnikov of Russia. Ehrlich established the concepts of antibodies and chemotherapy, while Mechnikov discovered phagocytosis. Their contributions form the two pillars of modern immunology: humoral immunity and cellular immunity. The first two chapters of a university-level immunology textbook begin with the stories of these two individuals.

Immunity Was Not One Thing

There are two main ways our body fights pathogens. One is when cells directly engulf and destroy the enemy (cellular immunity). The other is by creating chemical substances called antibodies that neutralize the enemy (humoral immunity). In the late 19th century, these two mechanisms were discovered separately, and the immunology community engaged in a heated debate for some time about “which one is the real immunity.”

If we use a CS analogy, this is a dual-layered security architecture. Mechnikov's phagocytes are like a firewall – they immediately block and eliminate any suspicious packet that comes in, regardless of its pattern. Ehrlich's antibodies are like the signature rule set of an IDS (Intrusion Detection System) – they precisely recognize a specific pattern (antigen) and provide a targeted response. Just as modern security is not complete with only a firewall or only an IDS, immunity is complete only when these two systems work together.

The Landscape of the Times — Europe on the Brink of War

1908 was the year that Europe stood on the countdown to World War I. The Bosnian Crisis erupted when Austria-Hungary annexed Bosnia and Herzegovina. Six years later, the assassination of an Austrian Archduke in Sarajevo, Bosnia, triggered World War I.

In Korea, the armed resistance movement was at its peak. Following the disbandment of the army in 1907, armed groups rose up across the country, and Japan suppressed them with the "South Korean Great Sweep Operation." Two years later (1910), the loss of sovereignty was imminent.

The awarding of the Nobel Prize to Ehrlich and Mechnikov reflects the scientific landscape of that era. Germany (Ehrlich) and Russia (Mechnikov) were politically antagonistic, but in science, they had to acknowledge each other's discoveries. Interestingly, Mechnikov left Russia and conducted his research at the Pasteur Institute in Paris. The nationality of a scientist and the location of their research are not always the same.

A Revolution That Began with Starfish — Mechnikov's Phagocytosis

Ilya Mechnikov (1845-1916) was born near Kharkiv, Russia. From an early age, he showed an almost obsessive interest in nature and taught zoology at the University of Odessa.

In 1882, while observing starfish larvae in Messina, Sicily, Mechnikov made a fateful discovery. He observed cells floating freely within the transparent body of the larvae, and when he inserted rose thorns into them, he saw the cells gather around the thorns and engulf them. "These cells eat the enemy!" Mechnikov named this phagocytosis. It means "eating cell" in Greek.

If we use a CS analogy, phagocytes are similar to a garbage collector. They automatically detect and remove objects (bacteria, dead cells) that are no longer useful or dangerous in the program (body). It doesn't use precise judgment like a reference count, but sweeps based on a simple criterion: "this is not mine (non-self)." However, this analogy breaks down here. Garbage collectors do not accidentally remove living objects, but phagocytes sometimes attack their own cells – this is an autoimmune disease.

However, at the time, the academic community, especially the Ehrlich faction in Germany, strongly opposed Mechnikov's phagocytosis theory. Ehrlich argued that "immunity is not caused by cells, but by chemical substances (antibodies) in the blood."

The Magic Bullet — Ehrlich's Chemotherapy

Paul Ehrlich (1854-1915) was born in Strehlen (now Poland) into a Jewish family. From his medical school days, he was fascinated by chemical dyes and devoted himself to experiments staining various tissues. This "dye obsession" became the root of all his subsequent achievements.

Ehrlich's key idea was the side-chain theory. The theory states that cells have receptors (side chains) on their surface, like keyholes, and that toxins or antigens bind to these keyholes, causing the cells to react and overproduce antibodies. Although the theory itself is not accurate from a modern perspective, the core insight that "antigen-antibody binding is based on chemical specificity" became the foundation of modern immunology.

If we use a CS analogy, Ehrlich's side-chain theory is the archetype of API endpoint matching. Receptors on the cell surface are API endpoints that accept only requests (antigens) of a specific shape, and antibodies are middleware that block requests that match those endpoints. "Not just any drug works for just any disease, but a specific chemical structure binds only to a specific target" – this was the principle that Ehrlich established.

The concept that emerged from this principle is chemotherapy. Ehrlich set a goal to find a "magic bullet" – a chemical substance that would precisely target pathogens without harming human cells. In 1901, Behring used "weapons from nature" (antitoxins), while Ehrlich sought "artificially created weapons" (synthetic drugs).

The result of this was Salvarsan (compound 606) in 1910 – the first case of a disease (syphilis) being treated with a synthetic chemical substance. The fact that it took 606 compounds to succeed shows how arduous a process drug development is. Ehrlich received the Nobel Prize in 1908, but his most famous achievement (Salvarsan) came two years later.

Cell vs. Humoral — The End of a 100-Year Debate

The debate between Ehrlich (humoral immunity) and Mechnikov (cellular immunity) was the most productive debate in the history of immunology. That's because they were both right.

Modern immunology knows that the two systems are not separate, but closely cooperate. Phagocytes engulf pathogens and then present the fragments to T cells (antigen presentation), and T cells activate B cells to produce antibodies. Mechnikov's phagocytes call Ehrlich's antibodies. Cellular immunity and humoral immunity were the front and back ends of the pipeline.

It is no exaggeration to say that Ehrlich is credited with "the whole world owes him" in his obituary in The Times. The principle he established, "that specific chemical substances attack only specific targets," is the foundation of the entire modern pharmaceutical industry. Targeted cancer therapies, monoclonal antibody drugs, and immune checkpoint inhibitors – all have their origins in Ehrlich's concept of the "magic bullet."

The Dual Defense of Immunity: Mechnikov's phagocytes (cellular immunity) are the first line of defense, immediately engulfing pathogens, and Ehrlich's antibodies (humoral immunity) are the second line of defense, precisely eliminating specific targets. Modern immunology understands the cooperation of these two systems integratively.