Immune system has been a complicated field of medicine ever studied. A lot of input was required to understand the various components of the immune system. Although Pasteur had proved that vaccination worked but he did not understand how.

Later, the experimental work of Shibasaburo Kitasato and Emil von Behring in 1890 gave the first insight into the mechanism of immune system, that earned von Behring the Nobel prize in Medicine in the year 1901.Von Behring and Kitasato had established that serum (this is the liquid, noncellular component of coagulated blood) from animals that were previously immunized to diphtheria could transfer the immunity to unimmunized animals. This experimental observations lead to the search of the protective agents in serum. Various researchers during the next decade verified that an active constituent of the immune serum had the tendency of deactivation and precipitation of toxins, and could even agglutinate bacteria. The active agents so found were named after the activity they exhibited, for example antitoxin, precipitin, and agglutinin, respectively.

Humoral Immunity
Formerly, it was thought that a different serum component was responsible for each activity, but during the 1930s, through the efforts of Elvin Kabat, it was established that only a fraction of serum which was first called gamma-globulin and now called as immunoglobulin responsible for all these activities. These immunoglobulin fractions consisted of active molecules called antibodies. Because the immunity was interceded by antibodies contained in body fluids which were known at the time as humors, it was called humoral immunity.

Cell-mediated Immunity
In the year 1883, before the discovery that immunity could be transferred by a serum component, Elie Metchnikoff had demonstrated that immune state of an animal can be also contributed by the cells. It was observed by him that certain white blood cells, which he phrased as phagocytes, were able to gulp down micro organisms and other foreign material. It was noted that these phagocyte cells were more vigorously active in animals that had been immunized; Metchnikoff hypothesized these cells as major effector of immunity rather than serum components. The active phagocytic cells that were identified by Metchnikoff were likely blood monocytes and neutrophils.

A controversy had developed between those who held to the notion of humoral immunity and those who settled with Metchnikoff’s perception of cell-mediated immunity. It was later shown that both are correct—immunity requires both cellular and humoral responses. Because of the technical problems, due to the lack of modern scientifically established biochemical techniques, much of the information about cellular immunity lagged behind findings that concerned humoral immunity.

In 1940s, in an experiment by Merrill Chase, it was successfully established that transferring immunity against the tuberculosis organism can be mediated by transferring white blood cells between guinea pigs. This demonstration helped to reawaken interest in cellular immunity.

In the 1950s, with the emergence of improved cell culture techniques, the lymphocyte was identified as the cell liable for both cellular and humoral immunity in the animals.
Soon thereafter, at Mississippi State University, experiments pioneered by Bruce Glick specified that there were two types of lymphocytes:
. T lymphocytes derived from the thymus mediated cellular immunity, and
. B lymphocytes derived from the bursa of Fabricius

The controversy concerning the functions of humoral and cellular immunity was resolved when the two systems were shown to be entwined, and that both systems were essential for the immune response.

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Lucas Beaumont
Generalist. Wikipedia contributor. Elementary school teacher from Saskatchewan, Canada.