**2. The human immune system**

The immune system plays an important role to protect the host from infectious agents such as bacteria, viruses, fungi and parasites. In addition, it is also important in the identification and

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elimination of tumor cells as well as in response to injury and trauma. Thus, an effective and efficient immune system is essential as a host defense mechanism against infectious diseases and cancer. The immune system can be further subdivided into innate and acquired or adaptive immunity (Table 1).


**Table 1.** Components of the innate and acquired immune systems [1].
