Components of Innate Immune System

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The page below is a sample from the LabCE course An Update on Basic Concepts of Immunity. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Components of Innate Immune System

There are many components of the innate immune system. A partial list along with a brief description of their function is listed in Tables 4-6. The following pages will then focus on just a few of these which might be less familiar to the reader: NK Cells, Complement, and Toll-like Receptors.
Table 4. Selected Cells of the Innate Immune System and their Function.
Cells
NeutrophilsPhagocytic cells which quickly enter site of infection in large numbers
MacrophagesPhagocytic cells resident in most tissues; have multiple receptors and are capable of antigen presentation to T lymphs, release of cytokines, and recruitment of other immune cells
NK CellsLarge non-specific granular cytotoxic lymphocytes; recognize intracellular infections and tumor cells and then kill them by inducing apoptosis.
Table 5. Selected Proteins and Peptides of the Innate Immune System and their Function.
Proteins/Peptides
Complement
A series of innate plasma proteins which become activated in a cascade fashion; these activated proteins then can enhance (“opsonize”) the pathogen for phagocytosis or directly perforate the pathogen cell membrane.
CytokinesA large variety of proteins secreted by cells which attach to receptors on other cells and lead to a specific activity in those other cells. For instance, cytokines will determine how a CD4 T Cell will differentiate.
Antimicrobial peptides
Soluble effector molecules, also known as “defensins” that protect mucosal surfaces by directly penetrating microbial membranes which can lead to destruction of many types of pathogens.
Other plasma proteins
Many proteins whose function is not directly part of the immune system, but play a role in defense; examples include fibrin, platelet granules, kinins, protease inhibitors, and others.
Table 6. Selected Receptors of the Innate Immune System and their Function.
Receptors
Toll-like receptors (TLRs)
A family of receptors found on macrophages, dendritic cells, neutrophils, and others which sense types of pathogen molecules called PAMPs - pathogen associated molecular patterns - (such as lipopolysaccharide from bacterial walls) and lead to the activation of that cell. These activities are also important for initiating the adaptive immune response.
Innate receptors
A wide variety of receptors such as complement receptors, lectins, and scavenger receptors (which can recognize pathogens’ nucleic acids and leipoteichoic acid.)