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Microbial agents and pathogens contain some molecules over their surface that act as foreign substance for the body and are collectively called as pathogen associated molecular pattern (PAMP). PAMP's are recognized by specific proteins and biochemical molecules produced by cells of innate immunity and these recognition molecules are called as pattern recognition receptors . The innate immune responses are produced against the specific structures present over the microbes and are common to many of them. Thus, they cannot distinguish the minute differences among microbes. In contrast, adaptive immunity is stimulated by constant exposure of infectious agents. The most characteristic feature of adaptive immunity is memory against the repetitive exposure of same pathogen. Furthermore, it has a capacity to distinguish between fine differences among microbes and hence also called as specific immunity . As specific immunity is gathered by constant exposure to the foreign agent, it is better termed as acquired immunity . The central components of adaptive immunity are

1)  Lymphocytes and their secreted products e.g. antibodies

2) Foreign substances that trigger specific immune responses and are identified by lymphocytes or antibodies are called as antigens .

 

Figure1.1 Graph showing the relation between innate and acquired immunity: