We, humans, live in a world full of microorganisms like bacteria, viruses many of whom cause infectious diseases. But, although we are exposed to these pathogens all the time, we rarely get infected or fall ill. Why? Our body has an immune system consisting of defense mechanisms that protect us against infections. The branch of biology devoted to studying our body’s defenses against infection is called immunology.
Immunology is a relatively new scientific discipline that arose during the latter half of the 18th century. The concept of immunity from disease, though, can be traced back to Greece in the 5th century BC. Thucydides, the famous Greek historian, wrote about individuals who had suffered and recovered from the plague and as a result, became immune to the disease. One of the earliest documented attempts at intentionally inducing immunity to a particular disease came from China. The process was called variolation. It involved exposing healthy people to substance collected from sores or lesions caused during diseases like smallpox, either by scratching it into the skin or blowing into the nostrils. Variolation went on to be practiced in different countries until vaccines started being developed.
Edward Jenner, an English physician developed a vaccine for smallpox using material obtained from pustules caused by cowpox, a milder disease that affected dairy maids who milked cows. He took the bold step of inoculating a young boy with cowpox. After six weeks, he observed that even after inoculation with smallpox, the boy did not develop the disease. Thus, inoculation with cowpox provided protection against smallpox, a dreaded disease of that era.
Jenner called this procedure ‘vaccination’. Gradually, vaccination became the widely accepted method of immunization for a number of infectious diseases. Almost two centuries and widespread immunization programmes later, in 1980, the World Health Organization declared the world free of smallpox.
Although the credit for introducing vaccines goes to Jenner, he did not know much about the infectious agents that caused diseases. It was the work of bitter scientific rivals Louis Pasteur, a French microbiologist and Robert Koch, a German physician in the late 19th century that helped shape the world’s understanding of infectious diseases. Their experiments had proven that the various infectious diseases that human beings suffered from were actually caused when different microscopic organisms invaded our bodies. These tiny yet harmful invaders were called germs or pathogens. The ‘germ theory of disease’ eventually became the accepted scientific theory for many diseases.
When the germs invaded, how did our bodies that act as host, defend itself? The germ theory did not answer this question. Ilya Metchnikoff, a Russian zoologist did while studying starfish larvae. He found a type of cell in the host that could engulf and digest the germs or particles that he had injected into the larva. Metchnikoff called them phagocytes meaning “devouring or eating cells”. Since these cells are always present in the body and ready to act, he believed them to be the first line of defence against pathogens.
It was around the same time that German biologist Emil Von Behring together with Shibasaburo Kitasato, a guest researcher from Japan discovered in Berlin that serum of animals immune to diphtheria contained soluble molecules that have an anti- diphtheria toxin activity. Today, we call these molecules ‘antibodies’. These discoveries gave rise to the study of immunology as we know it now, a study of the immune system’s component cells and molecules.
Over the decades, vaccination has been effective in protecting us from a number of devastating infectious diseases. Widespread immunization programmes against diseases have saved numerous lives. One such success story is the well-known Polio vaccination programme in India which led to WHO declaring the country to be polio- free in 2014. However,myths regarding harmful effects of vaccines continue to circulate in many countries all over the world causing many families to not vaccinate their children thus putting them at risk from many infectious diseases.