Acquired immunity is also known as adaptive or specific immunity. As the name specifies, it is capable of recognizing and selectively eliminating specific pathogens. Acquired immunity is a characteristic of vertebrates only. This kind of defense system is triggered in response to an exposure to a microorganism. However, specific defense mechanisms require several days to be activated. Following are some of the acquired immunity features:
Specificity: The immune system is capable of distinguishing various foreign molecules.
Diversity: It has the ability to recognize and distinguish a vast variety of foreign molecules.
Discrimination between self and non-self: It is able to recognize molecules that are foreign or non-self. In addition, it also recognizes self-bodies and does not harm them.
Memory: When the immune system first encounters a microbe or any foreign agent, it generates an immune response and finally eliminates the invader. The immune system retains the memory of its encounter with a particular pathogen. So, when the same pathogen comes in contact with the immune system, it recognizes it and evokes a heightened immune response.
Specific immunity is associated with two major groups of cells, which are lymphocytes and antigen-presenting cells. A healthy human body possess about a trillion lymphocytes. The lymphocytes are categorized into two types, which are T lymphocytes or T cells and B-lymphocytes or B cells. All these lymphocytes are produced in the bone marrow and the process of their production is called haematopoiesis.