Dr. Elie Metchnikoff

Hello! In this comprehensive article, we will focus on the extraordinary life of Dr. Elie Metchnikoff, his revolutionary contributions to immunology, and the process that led him to win the Nobel Prize in Medicine. A renowned scientist who shared the 1908 Nobel Prize in Medicine with Paul Ehrlich, Metchnikoff is known for pioneering work in the field of immunology, particularly with his phagocytosis theory, which laid the cellular foundations of the immune system, and his insight into the potential of probiotics, thereby shaping the development of modern immunology.

Biography of Dr. Élie Metchnikoff: Life, Education, and Career

Elie Metchnikoff (born Ilya Ilyich Mechnikov), born on May 15, 1845, in Ivanovka village, Kharkov Governorate of the Russian Empire (now Ukraine), was the youngest child of a family of five. His father, a Moldovan serving in the Imperial Guard, was often absent during his childhood and education due to his duties. His mother, Emilia Nevahovna, encouraged her son to pursue a scientific career in life sciences. A private tutor who taught the family motivated Metchnikoff particularly towards studying natural history, including botany and geology.

By the age of six Metchnikoff was already teaching his siblings and other children. At eleven, in 1856, he enrolled at the Kharkov Gymnasium, and at fifteen he became acquainted with the microscope. He then worked on cells and took private lessons in histology, the study of the microscopic structure of tissues. During this period he read Henry Thomas Buckle's History of Civilization in England and embraced its main thesis that the progress of civilization depends on the progress of science.

Throughout his life Metchnikoff held to an optimistic philosophy. He believed deeply that science had the power to solve society's problems and to contribute to the moral development of civilization. The outbreak of the First World War in 1914, however, horrified and distressed him, shaking his faith in the curative power of science. Metchnikoff was also interested in thanatology (the study of death) and believed that death could be regarded as a natural end.

Education Life

Metchnikoff graduated from the Kharkov Gymnasium in 1862. His mother wished to direct him toward medical studies, but reasoned that, given his sensitive nature, biology would be more suitable and persuaded him to take up that field. Metchnikoff agreed and enrolled at Kharkov University in 1863. During this time he published his first scientific paper, on the histology of a protozoan genus, Vorticella. He completed his university coursework in two years and then moved to Giessen, Germany, in 1865.

Academic Career

Metchnikoff completed his doctorate in 1867 and served as professor of zoology and comparative anatomy at Odessa University (1870–1882). However, he fell into disagreement with his colleagues and soon left Odessa to return to work at St Petersburg University. Living in poverty and isolation, Metchnikoff's eyesight and mental health deteriorated. During this period — when he was known by the nickname "Mercury" — he attempted suicide twice. He met Ludmilla Fedorovna and married her in 1869; because of Fedorovna's tuberculosis, he had to nurse her until her death.

In 1882, due to increasing political unrest in Russia, he left Odessa with his wife and established a private research laboratory in Messina, Italy. In Messina, observing mobile cells surrounding foreign substances in transparent starfish larvae, he developed the phagocytosis theory. Metchnikoff noted that the process resembled an inflammatory response found in animals with circulatory systems.

In 1886, he returned to Odessa and took charge of a bacteriological station designed to vaccinate people against rabies based on Louis Pasteur's initiatives in France. However, due to his colleagues' hostility towards him for claiming inadequate medical education and qualifications, he resigned from this position after a year.

In 1888, he began working at the Pasteur Institute, where he stayed for 28 years. He continued his research alongside his wife Olga and published numerous articles and books; most notably, "Immunity in Infectious Diseases," which was published in 1901.

Death

In his final days at the Pasteur Institute in Paris, he was moved to rooms adjacent to those where Pasteur spent his last days from their country house outside Paris in 1916, and died on July 15, 1916, due to heart failure at the Pasteur Institute. Historians have described Metchnikoff as a tall, unkempt-haired figure with pockets full of scientific notes and papers.

Groundbreaking Research in Immunology

Metchnikoff is regarded as the "father of natural immunity." He was interested in microorganisms and especially in the immune system. He discovered phagocytosis after carrying out experiments on starfish larvae in Messina.

The Origin of Fagotage Theory

In 1882, while working in Messina, Italy, he made groundbreaking contributions to immunology through his experiments on starfish larvae. By inserting small foreign objects (such as citrus nematodes) into the transparent starfish (bipinnaria) larvae' bodies, he observed that mobile cells gathered around these objects shortly thereafter. He hypothesized that these "eating" cells might be the primitive equivalent of leukocytes in higher organisms, engulfing and destroying foreign substances entering the body. Metchnikoff named these cells phagocytes (from the Greek phagein, meaning "to eat") and called the process they carried out phagocytosis. In 1883, he presented this finding to scientists in Odessa, demonstrating that inflammatory responses could occur through cell migration even in an acellular starfish.

Elie Metchnikoff suggested that the process resembled an inflammatory response found in animals with circulatory systems. He presented his findings at Odessa University in 1883. His theory that some white blood cells could engulf and destroy harmful particles like bacteria was met with skepticism by leading experts, including Louis Pasteur, Emil von Behring, and others. At the time, many bacteriologists believed that white blood cells ingested pathogens and then disseminated them throughout the body.

He proposed the term "phagocyte" to Professor Carl Friedrich Wilhelm Claus at Vienna University for a cell that could surround and kill pathogens. The theory that some white blood cells could engulf and destroy harmful objects such as bacteria was met with skepticism by leading experts including Louis Pasteur, Emil von Behring, and others. At that time, most bacteriologists believed that white blood cells ingested pathogens and then disseminated them throughout the body.

Ilya Ilyich Metchnikoff proposed that the motile cells found in starfish larvae served as an ancestral defense mechanism against foreign organisms, similar to the primitive digestive function seen in higher animals, which originated from mesodermal cells.

The Role of Fagocytosis in the Immune System

Phagocytosis is an essential component of the immune system. Various immune cells such as neutrophils, macrophages, dendritic cells, and B lymphocytes perform phagocytosis. The act of phagocytosing pathogenic or foreign particles enables immune cells to know what they are fighting against. By recognizing the enemy, immune cells can specifically target similar particles circulating in the body. Another function of phagocytosis in the immune system is to engulf and eliminate pathogens (such as viruses and bacteria) and infected cells. Metchnikoff was also the first person to distinguish between macrophages and microphages.

Phagocytosis is the primary mechanism used by the immune system of multicellular organisms to remove pathogens and cellular debris. Swallowed material is then digested in the phagosome. Bacteria, dead tissue cells, and small mineral particles are examples of objects that can be phagocytosed. Some protozoans use phagocytosis to obtain food.

Phagocytosis is today described in detail as a basic component of immunity. Phagocytic cells (e.g. neutrophils, macrophages) recognize microbes through receptors on their surfaces. Direct recognition can occur through pattern-recognition receptors (e.g. toll-like receptors, scavenger receptors) that detect molecular motifs common to pathogens. In addition, mediators called opsonins facilitate phagocytosis: coating microbes with antibodies (especially IgG) or complement proteins enables phagocytes to bind their targets more tightly through Fc and C3b receptors. After binding to the microbe, the phagocyte reorganizes its actin cytoskeleton to form pseudopods and takes the microbe into a vesicle called a phagosome. The phagosome then fuses with the cell's lysosomes to form a phagolysosome, in which antimicrobial molecules such as acidic enzymes (e.g. lysozyme) and reactive oxygen species become active and break down the microorganism. The resulting waste material is expelled from the cell by exocytosis. Although this molecular mechanism was unknown in Metchnikoff's day, it is the basis of the "cell that eats foreign material" phenomenon that he observed.

The Debate Between Humoral and Cellular Immunity

At the end of the 19th century and at the beginning of the 20th century, immunology was the scene of intense debate between cellular and humoral theories. While Russian zoologist Elie Metchnikoff argued that immunity essentially originated from cells, his contemporaries such as German physician Paul Ehrlich and Emil von Behring advocated for the humoral theory, which posited that soluble molecules in the blood serum (antibodies) fought off infections.

The theory of heterochrony explained that the body produced antibodies in a chain-like structure specific to each pathogen, neutralizing toxins by producing them. Von Behring demonstrated the power of humoral immunity in rendering toxins ineffective without killing the disease-causing agents themselves through his antitoxin sera developed for diphtheria and tetanus in 1890. In contrast, Metchnikoff and his supporters argued, based on experimental evidence, that cellular immunity was responsible for eliminating microorganisms, as phagocytic cells engulfed and destroyed them.

The disagreement between the two sides sparked a sharp debate in the scientific community, known as the "antibody wars." Some leading bacteriologists of the time (including figures such as Louis Pasteur and von Behring) initially approached Metchnikoff's ideas with skepticism; while many accepted that phagocytes consumed bacteria, they claimed this was harmful rather than beneficial, arguing that it helped spread the microbe. Despite criticism, Metchnikoff continued his work, insisting that cellular mechanisms played a decisive role in fighting infection.

In 1908, the Nobel Committee effectively declared a ceasefire by awarding the Nobel Prize in Medicine to both Metchnikoff and Ehrlich, thereby validating that both approaches were complementary components of immunity. This led to official recognition for the cellular theory of immunity.

Ultimately, modern immunology integrated innate and adaptive immunity concepts by combining Metchnikoff's cellular theory with Ehrlich's humoral theory, thereby embracing the comprehensive understanding that the immune system functions through both cells and molecular factors, which is the scientific legacy of this historical debate.

Cellular Immune Acceptance and Tolerance Process

Initially, the majority of the scientific community, particularly due to the success of serum treatments, gave weight to the humoristic view. The miraculous effect of diphtheria antitoxin in the 1890s and the ability to measure antibodies in the laboratory increased interest in the liquid components of immunity. By the early twentieth century, some scientific findings narrowed the gap between the two views. In 1895, Belgian Jules Bordet showed that a component he called complement in blood serum could break down bacteria; complement was a serum factor that enhanced the effectiveness of antibodies in killing microorganisms. Shortly after, British researcher Almroth Wright reported that immune serum contained substances called opsonins that made bacteria more ingestible for phagocytes.

These findings revealed that antibodies (humoral) actually work together with phagocytes (cellular) by collaborating, reconciling both theories. It was now understood that antibodies help phagocytes recognize and engulf microbes more easily by encapsulating them. This led to the concept that the immune response consists of both cellular and humoral components.

Effects on Modern Immunology

Cellular and humoral immunity debates laid the foundations for the principles of immunology. The opposing views of Metchnikoff and Ehrlich accelerated immune research from two sides. Ultimately, both approaches were partially correct, and today the distinction between innate immunity (natural/cellular) and adaptive immunity (acquired/humoral) has become a central concept in immunology.

The Productive Studies at Pasteur Institute

Inspired by the work of Metchnikoff, Louis Pasteur embarked on developing practical solutions against infectious diseases.

Contributions to Rabies Vaccine and Infectious Diseases

After successfully applying the rabies vaccine in 1885, Metchnikoff returned to his homeland Russia and established a rabies vaccination station in Odessa based on Pasteur's method. However, due to lack of formal medical training, he faced obstacles from his colleagues and left this position. In 1888, he joined the newly founded Pasteur Institute in Paris at Pasteur's invitation and conducted research there until the end of his life (1916).

At the institute, he worked alongside other prominent microbiologists of the time (for example, Émile Roux, Charles Chamberland, Emile Duclaux). In addition to immunological theories, Metchnikoff was also interested in preventing and treating various diseases directly here. For instance, he researched ways to develop immunity against epidemics such as cholera and typhoid fever along with his students. Metchnikoff also contributed to finding practical solutions for difficult diseases like syphilis: he tested whether a mercury compound-based remedy could prevent or prevent the spread of syphilis with his colleague Émile Roux. Although this work did not prove as effective as Ehrlich's magic bullet (Salvarsan) later on, it drew attention as an early initiative in prophylaxis against sexually transmitted diseases.

Elie Metchnikoff's work at the Pasteur Institute was known for producing ideas on diseases such as plague, cholera, typhoid fever, and tuberculosis that were prevalent during his time, as well as publishing articles related to strategies for conferring immunity against these diseases. Consequently, his research at the Pasteur Institute touched not only theoretical immunology but also public health and preventive medicine.

Breakthroughs That Led to the Nobel Prize and Their Scientific Impact

In 1908, when Metchnikoff received the Nobel Prize in Physiology or Medicine together with Paul Ehrlich, the Nobel Committee announced that it was awarded to him for his work and discoveries in immunology. Specifically, the discovery by Metchnikoff of phagocytic cells similar to amoebas in animals that consume foreign particles and their role in fighting infections was the most significant step towards the award.

The Nobel Prize honored the two founders of immunology, Metchnikoff (cellular immunity) and Ehrlich (humoral immunity), by emphasizing the comprehensive development of immunology. Metchnikoff's discovery revealed an innate mechanism that living organisms had evolved to defend themselves against microbes for the first time.

In summary, Metchnikoff's work that extended to the Nobel Prize included the discovery of phagocytes' ability to eliminate microorganisms, among many fundamental concepts related to the immune system. His research laid the groundwork for an approach that considers both cellular and humoral components of immune responses together. The Nobel Prize has highlighted the magnitude of Metchnikoff's scientific legacy and elevated him to the status of father of natural immunity.

The General Scientific Atmosphere at Pasteur Institute and the Role of Metchnikoff

The late 19th century was the golden age of fighting infectious diseases; the Pasteur Institute was at the forefront of this fight. When Metchnikoff arrived in Paris, rabies vaccinations were already being administered here, and treatments for diphtheria were being developed using serums. This environment allowed him to test his own theories and stay close to practical application.

The Pasteur Institute, being an environment where interdisciplinary interaction is high, allowed Metchnikoff to situate his work within a broad perspective. For example, he began to think that infection was related not only to the interaction between microbes and hosts, but also to environmental and life factors. His work at the Pasteur Institute contributed to controlling deadly diseases such as rabies during that time, while also providing deep insights into the nature of the immune system. The presence of Metchnikoff at the Pasteur Institute served as an inspiration for young scientists; researchers who would later make significant discoveries were influenced by his laboratory and ideas. As a result, Metchnikoff did not only develop his own theories at the Pasteur Institute, but also laid the groundwork for a generation of scientists and made lasting progress in fighting infectious diseases.

Gut Microbiota and Probiotics Research Studies

In the last years of his life Metchnikoff turned to considering the concept of immunity from a broader perspective of biological integration. He was particularly drawn to the relationship between intestinal flora and aging.

Exploring the Connection Between Gut Bacteria and Healthy Living

In the early 1890s, during a cholera outbreak in France, he made an interesting observation: while people exposed to the same conditions of cholera bacteria did not fall ill at all, others suffered severely. Metchnikoff thought that this difference might be due to the microbial communities in their intestines (microbiota). To test his hypothesis, he conducted a bold experiment: he ingested a culture containing cholera vibrios himself; he remained unaffected. He also performed the same experiment on two volunteers, one of whom showed no symptoms while the other fell seriously ill with cholera. Based on these results, Metchnikoff concluded that beneficial and pathogenic bacteria could coexist in the gut, and that individuals with a rich population of beneficial bacteria would experience milder illnesses. This was his first scientific inference regarding the impact of gut microbiota on human health.

Following this, he also examined aging and general health in relation to microbiota. According to Metchnikoff, certain proteolytic bacteria living in the colon produce toxic metabolites over time, causing harm to the body and contributing to aging. He proposed that blocking these harmful effects could be achieved by dominating beneficial bacteria in the gut. Notably, the observation of Bulgarian villagers consuming large amounts of yogurt and living healthy and long lives caught his attention. He believed that the lactic acid-producing bacteria contained in yogurt (Lactobacillus delbrueckii subsp. bulgaricus, known as Bulgarian bacillus) prevented putrefaction in the gut.

In his 1903 work The Nature of Man, and in his 1907 publication The Prolongation of Life, Elie Metchnikoff presented detailed views on how human lifespan could be extended through manipulation of gut flora. In this context, he made fermented milk (sour milk/yogurt) a daily habit, believing it to be beneficial for his health. He named the concept of suppressing pathogenic bacteria in the intestines with lactic acid bacteria orthobiotics, essentially referring to establishing a balance between microorganisms and a healthy lifestyle.

Elie Metchnikoff was one of the scientists who discovered the concept of gut microbiota and its relationship to host health. Although his ideas were not fully understood at that time, he was quite visionary for his era: He had already proposed the idea of protecting health through friendly bacteria even back then.

Impact on Modern Probiotic Research

Ilya Mechnikov's predictions about gut bacteria were largely overlooked by the scientific community for decades after his death. With the discovery of antibiotics and hygiene theories gaining prominence in the mid-20th century, the idea of beneficial microbes fell into the background. However, experimental studies on microbiota from the 1990s revived Mechnikov's century-old ideas.

Probiotics, which refers to beneficial microorganisms for human health, has become popular in modern medicine and directly stems from the work of Metchnikoff. For example, certain strains of bacteria such as Lactobacillus and Bifidobacterium are used in probiotic products to maintain gut balance and provide protective effects against diseases. Metchnikoff's recommendation to consume yogurt has found its way into probiotic yogurts and kefirs today. Research has shown that some probiotics can prevent diarrhea, correct antibiotic-related gut imbalances, and even investigate approaches in the areas of mental health (microbiome-gut-brain axis) and immunological disorders.

Notably, Metchnikoff was one of the pioneers in the field of gerontology (gerontology, the study of aging) in the early 20th century, being among the first to use this term, and he proposed gut microbiota modulation as a solution for this area.

The Impact of Metchnikoff's Work on Modern Medicine

Elie Metchnikoff's theories and findings have become one of the fundamental bases for today's clinical applications.

The Legacy of Metchnikoff in Clinical Immunology

The importance of phagocytic cells in resistance to infections is well known in clinical practice. Patients suffering from severe neutropenia (neutrophil deficiency) can contract serious infections even with minor microbes, thereby confirming the vital role of phagocytosis as shown by Metchnikoff. Doctors assess a patient's defense status by performing white blood cell and neutrophil counts; if these are insufficient, appropriate protective measures are taken.

In modern clinical immunology, the concept of innate immunity is based on the ideas of Metchnikoff. In chronic granulomatous diseases such as Granulomatosis with Polyangiitis, patients frequently develop abscesses and granulomas due to defects in the killing mechanisms of phagocytes; this syndrome demonstrates that genetic disorders of the phagocytic mechanism can lead to immune system collapse, thereby validating Metchnikoff's findings in a clinical context.

Gut Microbiota and Immune System

Elie Metchnikoff's suggestion that beneficial gut bacteria support health has striking implications in modern immunology. Research has shown that the gut microbiome plays a critical role not only in digestion but also in the development and regulation of the immune system. The composition of gut flora enables the education and tolerance of immune cells. For example, a healthy microbiota stimulates the production of IgA antibodies in the intestinal mucosa, thereby preventing the entry of harmful microorganisms; it also competes against pathogens such as Clostridium difficile by inhibiting their excessive proliferation and even reducing the effects of cholera toxin. Disbiosis, or an imbalance in the microbiota, has been linked to various issues including inflammatory bowel diseases, allergies, and autoimmune disorders. Metchnikoff intuitively grasped this reality and proposed the concept of microscopic helpers within us.

Recent scientific studies in this field have been confirming his predictions made years ago: The gut microbiota not only forms a defense barrier against infections but also plays a crucial role in ensuring our immune system functions properly.

Current Research on Fagocytes and Macrophages

Metchnikoff's phagocytes, which he named, remain at the center of ongoing research today. Specifically, macrophages take on critical roles not only in infections but also in cancer, autoimmunity, and tissue regeneration among various other conditions.

Cancer immunotherapies involve strategies to reprogram macrophages (TAMs) that dominate around tumors, which can aid tumor growth, by modulating their activity.

Metchnikoff's legacy can also be seen in vaccine research: It has been understood that to achieve a strong vaccine response, antigen-presenting cells such as macrophages and dendritic cells need to be properly stimulated. This is why many modern vaccines contain adjuvants – substances that trigger innate immunity.

These examples demonstrate how extensively Metchnikoff's discovery of cellular immune mechanisms has impacted medicine. Researchers continue to study the intricacies of phagocytosis, seeking to develop treatments that enhance or inhibit this process.

The Legacy of Metchnikoff in Infection Diseases, Autoimmune Diseases, and Vaccine Development Processes

Infection prevention and control strategies have been deeply influenced by the findings of Metchnikoff. The knowledge that phagocytes are the cells that first encounter pathogens at the onset of an infection has led to numerous applications, from antimicrobial treatments to immunostimulatory methods. For example, immunostimulation therapies administered to patients with severe bacterial infections (such as increasing neutrophil production using granulocyte colony-stimulating factors) are based on Metchnikoff's principles.

The general approach to preventing infectious diseases through vaccination (immunization) and treatment (immunotherapy), balancing the immune system in autoimmune disorders, and immunological approaches to cancer all follow the trail of Metchnikoff's discoveries.

The Contemporaries of Metchnikoff and His Scientific Legacy

Metchnikoff interacted with many of the leading scientists of his time and worked closely with some of them.

Collaborators and Names He Has Worked With

While working at the Pasteur Institute in Paris, I was under the same roof as the institute's founder Louis Pasteur and his right-hand man Émile Roux. At the institute, French immunologist Jules Bordet also worked alongside young researcher Elie Metchnikoff during the same period. British physician Sir Almroth Wright was a contemporary of Metchnikoff and discovered opsonins that aid phagocytes, contributing to cellular-humoral synergy. Although German physician Emil von Behring and Japanese microbiologist Shibasaburo Kitasato worked on diphtheria-tetanus antitoxins while being somewhat distant from Metchnikoff's cell-based views, they indirectly competed with him in shaping immunity science. Paul Ehrlich can be remembered both as a rival and colleague; his scientific correspondence and debates played a critical role in shaping immunology.

In summary, Metchnikoff interacted with many scientists from his generation to establish an immunity school, directly or indirectly influencing their work.

The Impact on Future Generations and Scientific Heritage

Ilya Ilyich Metchnikoff's work served as a source of inspiration for subsequent generations of immunologists. In 1996, Charles Janeway and Ruslan Medzhitov identified Toll-like receptors in human immunity, thereby revealing the molecular basis of innate immunity, which was initiated by Metchnikoff 100 years earlier. When their discovery was awarded the Nobel Prize in 2011, laureate Jules Hoffmann specifically highlighted Metchnikoff's work, emphasizing that he was the first researcher to study innate immunity. Indeed, Metchnikoff is now regarded as the father of natural immunity.

Reception of His Work in Historical Context

Metchnikoff's work initially received mixed reactions during his time. By the 1900s, he had become an international figure; he was even referred to as the "microbe eater" in popular media.

Historically, Metchnikoff's work is considered a cornerstone of immunology. His name lives on in many places today: The Odessa University in Ukraine has been named after him as Mechnikov University, while infection disease institutes in Russia and France bear his name. In the history of immunology, Metchnikoff is always mentioned alongside Louis Pasteur, Robert Koch, and Paul Ehrlich as one of its co-founders.

Other Areas of Interest: Aging and Probiotics

Elie Metchnikoff, aging issues with which he was also concerned. As the pioneer of gerontology, Metchnikoff is considered the first person to use the term "gerontology." He developed a theory that aging is caused by toxic bacteria in the intestines and that lactic acid can extend life. He believed that future generations could live up to 150 years old. He linked the longevity of Bulgarian peasants to their consumption of yogurt containing Bulgarian bacteria (now known as Lactobacillus delbrueckii subsp. bulgaricus). To verify his theory, he drank sour milk every day throughout his life. He believed that healthy and long life requires replacing harmful microorganisms in the intestines with beneficial ones (such as eating yogurt or drinking sour milk).

A Visionary for Modern Medicine

Elie Metchnikoff left behind an incredibly rich scientific legacy. His discovery of phagocytosis and the cellular immunity principle has not only influenced his contemporaries but continues to inspire current research even after passing a century. This legacy holds an indispensable position in shaping the concept of immunity in modern medicine and biology.

Metchnikoff supported his theories with experimental data and set out the basic principles of the immune system. His work is the forerunner of much of today's research on innate immunity. In particular, his investigations of phagocytosis and probiotics carry significant potential for the development of new therapeutic approaches and the prevention of disease.

Publications and Awards of Metchnikoff

Metchnikoff published his scientific work in many articles and books. His best-known works include:

• Immunity in Infectious Diseases (1901)
• The Nature of Man (1903)
• The Prolongation of Life (1907)

Beyond the Nobel Prize, Metchnikoff received many other awards and honors. These reflect the extraordinary contributions he made to the world of science.

Conclusion: The Bright Face of Immunology and a Humanist Scientist

Dr. Élie Metchnikoff is exemplary not only for his theory of phagocytosis but also for his scientific rigor, his vision, and his ideal of serving humanity. This visionary, who laid the foundations of modern medicine and shed light on the complex world of the immune system, has left behind an enduring legacy. His work will continue to inspire future scientists and medical professionals and to contribute to human health.