Introduction

The word Innate means something that has been present since the birth. Hence innate immunity is the first line of defence that our body has from foreign elements. This type of immunity is non-specific in nature that is it acts against a vast array of microorganisms, fungi and bacteria. In other words, we can say that this immunity is general in nature and protects against outside pathogens by working as a first line of defence barrier.

Immune system

The immune system works to give protection of our body from harmful pathogens by boosting our defence system. There are two different types of immunity- Innate (inborn) and adaptive (adapted within the body from outside by humans gradually).

Innate immunity

Definition: Innate immunity is the thing that is born immunity grown from the inside without any dependency on antigens. It is strong and passes from one generation to another.

The common physical barriers to innate immunity are skin, epithelial tissues, mucous etc. The main cellular components that are associated with innate immunity are dendritic cells, macrophages, neutrophils, eosinophils, monocytes, and phagocytic cell enzymes like lysozyme.

Recognition of pathogens

Pattern Recognition Receptors (PRRs)

Pattern Recognition Receptors are a class of protein which plays a crucial role in the innate immune system. These receptors help in the detection of pathogens by recognising the specific molecular patterns known as pathogen-associated molecular patterns (PAMPS) and damage-associated molecular patterns (DAMPS) which are present in many pathogens like bacteria, fungi and other pathogenic microorganisms. 

This receptor can identify all the pathogens that are associated with PAMPS and DAMPS. After recognition, the pathogens are carried through the PRRS, and activation of the PRRS on the immune cells starts by working as the first line of defence barrier of innate immunity.

There are different types of PRRs like Toll-like receptors, C-like Lectin Receptors, NOD receptors etc. Now mainly we should focus on TLRS.

TOLL-Like receptors (TLRS)

Toll-like receptors are different classes of proteins. The term toll comes from the toll gene of Drosophila which works as the first line of defence barrier in innate immunity. Some different classes of TLRS are

• TLR1 and TLR2 are located in the cell surface working as heterophilic dimers.
• TLR1 binds with TLR 2 and TLR 2 binds with TLR 1 and TLR 6.
• TLR 7 AND TLR 8 identify imidazoquinoline which is a type of synthetic compound located at endosome.
• TLR 5 is located at the endosome that activates lung epithelial cells to induce inflammatory cytokines.

 TLR Signalling

TLR works when transcription factors like NF-KB, IRF, and Dendritic cells work and dictate the immune cells to start the innate immune response.

Innate immune responses

• Interaction of innate immunity with adaptive immunity

Innate immunity can always interact with adaptive immunity by working through Antigen-presenting cells (APC).

Write about this APC and the 4 main types of cells 

• Role of Dendric Cells in innate immune response 

Dendritic cells are one of the major cells that work as major antigen-presenting cells (APC) where the cells can induce B cell and T cell response. With the help of T cells and B cells, the inflammatory response starts. CD 8 cells activate cytotoxic T cell activation and CD 4 cells activate naïve (what is this naive?) T cell activation and also the formation of B cells.

• Genetic Bases of Innate Immunity

The main genetic basis of innate immunity are activation of Pathogen Recognition Receptors (PRRS) like Toll-Like Receptors (TLR) where antigen-presenting cells like dendritic cells (DC) are activated and ultimately activate transcription factors like NF-KB, and IRF. All the PRR molecules are located in the pathogen and damage-associated molecular patterns (PAMPS) (DAMPS).

Disorders

Some of the disorders that can be found regarding innate immunity like asthma, allergies, and HIV infections. 

Drugs based on TLR therapies, and immunoglobulin therapies can treat immune disorders very well.

 Some Current Research on Innate Immunity 

• During the pandemic situations like to fight against the SARS-COV2 virus innate immunity, new mechanisms have arrived to fight against the virus.
• Regarding Toll-Like Receptors, what changes can be done and modifications can be done regarding the TLRS that was also going to be researched.
• PRRS binding mechanisms with the antigens were also a part of the current research topic.
• Research on what are the new modern strategies of innate immune responses is also going on.

Q&A

1. What is Innate Immunity?

Innate immunity is the inborn immunity that is not adapted from outside sources and it works as the first line of defence barrier to fight against the pathogens. Ex- cough, sneezing etc.

2. What is Innate Immunity specific?

Specific innate immune response means they are specific to the particular infected cells and works on those cells as the first line of defence barrier system.

3. Is Innate Immunity present at birth?

Innate Immune cells like neutrophils and monocytes are present in the neonatal stage but in lower working powers than in the adult stage.

4. When Innate Immunity is activated?

When the pathogens are infected inside the healthy cells then the APCs like DC, PRRS (TLRS) recognize the pathogens associated with PAMP and DAMP to activate the immune response by initiating the transcription factor immune response like NF-KB, IRF etc.

5. Does Innate Immunity produce antibodies?

When the transcription factors start their action for an immune response then the T cell activation and B cell formation also start to kill the pathogens. From the B cell antibody production starts.

6. What does Innate Immunity mean?

It means that are born built immunity inside our body and it is not adapted. Ex- cold, cough, etc.

Summary

• Innate immunity plays a great role in creating immune response 
• It works as the first line of defence system to fight against the pathogens. 
• Various defence mechanisms are there like pathogen recognition receptors, toll-like receptors etc. to activate transcription factors like NF-KB, and IRF.
•  Also the activation of T cells and B cells like activation of cytotoxic T cells and antibody production through B cells.
• Examples like cough, sneezing etc. Sometimes many disorders happen like asthma, allergy where it can be treated with TLR drugs, Immunotherapies etc.

References

1) Kuby Immunology.

2) Akira S, Uematsu S, Takeuchi O. Pathogen recognition and innate immunity. Cell (2006) 124:783–801. doi:10.1016/j.cell.2006.02.015

3) Collin M., Bigley V., Haniffa M., Hambleton S. Human dendritic cell deficiency: The missing ID? Nature Reviews Immunology. 2011;11:575–583.

Written By: Shreya Banerjee