الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
The immune system refers to a collection of cells and proteins that function to protect the skin, respiratory passages, intestinal tract and other areas from foreign antigens, such as microbes (organisms such as bacteria, fungi, and parasites), viruses, cancer cells, and toxins.
The immune system can be simplistically viewed as having two “lines of defense”: innate immunity and adaptive immunity.
Innate immunity represents the first line of defense to an intruding pathogen. It is an antigen-independent (non-specific) defense mechanism that is used by the host immediately or within hours of encountering an antigen.
Adaptive immunity, on the other hand, is antigen-dependent and antigen-specific and, therefore, involves a lag time between exposure to the antigen and maximal response. The hallmark of adaptive immunity is the capacity for memory which enables the host to mount a more rapid and efficient immune response upon subsequent exposure to the antigen.
Recognition of a wide range of molecular structures that presents in different microorganisms is dependent on a diverse set of germ line encoded receptors, termed pattern recognition receptors (PRRs). These receptors are expressed by a variety type of cells — especially the innate immune system cells, such as dendritic cells (DCs) and macrophages — and they act to sense danger or damage signals.
Toll-like receptors (TLRs), the best characterized PRRs, were first reported in humans in 1998 These receptors are a family of type I transmembrane glycoproteins comprised of an extracellular domain with leucine-rich repeat (LRR) motifs, and a Toll/interleukin-1 receptor (IL-1R) - interacting (TIR) domain with at least 11 members in human and 13 in mouse, which leads to intracellular signaling and play an important role in both innate and acquired immune responses.