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3.2.2 Antiviral defense

These are the responses against viral infection and are mediated by cytokines and natural killer cells. Pathogens which are able to survive against inflammation and antiviral defense in turns enter into blood circulation. Blood contains another important component of innate immunity called complements. The pathogens are destroyed by typical classical and alternate pathways of the complement system (lecture 4). The innate immune responses many time fails to eradicate the pathogens. In those cases the immune system is evolved with more robust and powerful cells and antibodies of adaptive immune system.

 

3.3 Recognition system of innate immunity

Innate immune system recognizes the structures present on the microbial pathogens and are collectively called pathogen associated molecular pattern (PAMP). Similarly innate immune system also recognizes the molecules produced by the damaged cell and are collectively called damage associated molecular pattern (DAMP). The PAMP and DAMP are collectively called pattern recognition receptors . The receptors for innate immune system are developed at the level of germline (adaptive are generated by somatic recombination). The innate immunity does not react with the normal and healthy cells.

 

3.4 Toll like receptors

Toll like receptors (TLRs) are the families of PAMP expressed in many cell types and are involved in the recognition of various kind of antigens. The gene for TLR was first discovered in Drosophila. There are nine different kinds of TLRs (TLR1-9) each recognizing different antigenic molecules. TLR contains leucine repeats and cysteine rich motif at their extracellular domain while intracellular domain contains toll IL-1 receptor (TIR). The extracellular part of TLR is involved in ligand binding while the intracellular domains are involved in the downstream signaling cascade.