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INTRODUCTION

We constantly being attack by infectious agent and yet we still able to resist it. It is because the

response of our immune system. Our immune system is divide into two major subdivisions that

is innate immune system and adaptive immune system. Innate immune system is nonspecific and

acts as the first line defense against invading organism. Meanwhile, adaptive immune system or 

specific immune system acts as second line defense that attack specific to the invading pathogen.

The response is much slower than innate immunity but it will memorize the pathogen that has

 been countered and reacts more quickly when the same pathogen is found.

 

Background

The innate immune system serve as first line defense and have anatomic, humoral and cellular 

 barriers features that function as barriers to infection.

Anatomic barriers

The first line of defense of the body is the skin and other anatomic barriers to invasion. These

include tears, saliva, mucus and cilia in the intestinal and respiratory tracts.

Humoral barriers

If the pathogen able to penetrate the anatomic barriers, acute inflammation takes over which is

characterized by edema and phagocytic cells. These humoral factors are found in serum or they

are formed at the site of infection.

Cellular barriers

Part of the inflammatory response is the recruitment of 

 polymorphonuclear eosinophiles and macrophages to sites of infection. These cells are the main

line of defense in the non-specific immune system.

•  Neutrophils: These phagocytes patrol the body searching for pathogens, engulf and killinvading organisms and contribute to damage to healthy tissue during inflammation.

• Macrophages: These phagocytes engulf and kill microorganisms. They are able to travel

outside of the circulatory system by moving across the cell membrane of blood vessels.They contribute to tissue repair and can present antigens to elements of the adaptive

immune system. Macrophages also secrete chemicals that kill microorganisms and can

 provoke inflammation.

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• Dendritic cells: These phagocytes contact with the external environment. They are very

important in engulfing and presenting antigens to cells of the adaptive immune system;

they serve as a link between the innate and adaptive immune systems.

•  Natural Killer (NK) cells: These, and related cells, nonspecifically kill cells that have

 been infected by viruses or tumor cells. They are able to differentiate between self andforeign by the presence or absence of MHC-class I molecules. Healthy cells express

MHC class I molecules on their surface, but virus-infected and malignant cells greatlyreduce their expression, so natural killer cells will eliminate the infected cells. These cells

are an active subject of investigation because they are able to differentiate between self 

and nonself – a process that goes awry in autoimmune disease.

•  NKT cells: These cells exhibit characteristics that place them at the border betweeninnate and adaptive immunity. A growing number of autoimmune diseases have been

linked to a failure to regulate these cells.

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ANATOMICAL BARRIERS

A. SKIN

The skin, consisting of the epidermis and the dermis, is dry and acidic. These conditions

are not favorable to bacterial growth. Normal flora of the skin also inhibits potentially

harmful microbes. In addition, the dead, keratinized cells that make up the surface of the

skin are continuously being sloughed off so that microbes that do colonize these cells are

constantly being removed. Hair follicles and sweat glands produce lysozyme and toxic

lipids that can kill bacteria. Epithelial cells also produce defensins and cathelicidins to

kill microbes. Beneath the epidermis of the skin are Langerhans' cell which is immature

dendritic cells that phagocytose and kill microbes, carry them to nearby lymph nodes, and

  present antigens of these microbes to T-lymphocytes to bergin adaptive immune

responses against them. Finally, T-lymphocytes and B-lymphocytes are associated with

the epidermis and the mucosal epithelium. These cells recognize microbes common to the

epidermis and mucous membranes and start immediate adaptive immune responses

against these commonly encountered microbes.

B. MUCOUS MEMBRANES

Mucous membranes line body cavities that open to the exterior, such as the respiratory

tract, the gastrointestinal tract, and the genitourinary tract. Mucous membranes are

composed of an epithelial layer that secretes mucus, and a connective tissue layer. The

mucus is a physical barrier that traps microbes. Mucus also contains lysozyme to degrade

 bacterial peptidoglycan, an antibody called secretory IgA that prevents microbes from

attaching to mucosal cells and traps them in the mucous, lactoferrin to bind iron and keep

it from from being used by microbes, and lactoperoxidase to generate toxic superoxide

radicals that kill microbes. Resident normal flora of the mucosa also inhibit potentially

harmful microbes. In addition, the mucous membrane, like the skin, is constantly

sloughing cells to remove microbes that have attached to the mucous membranes.

Beneath the mucosal membrane is mucosa-associated lymphoid tissue (MALT) that

contains Langerhans' cells - immature dendritic cells that phagocytose and kill microbes,

carry them to nearby lymph nodes, and present antigens of these microbes to T-

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lymphocytes to bergin adaptive immune responses against them. Intraepithelial T-

lymphocytes and B-1 lymphocytes are associated with the epidermis and the mucosal

epithelium. These cells recognize microbes common to the epidermis and mucous

membranes and start immediate adaptive immune responses against these commonly

encountered microbes

MECHANICAL REMOVAL.

A. MUCUS AND CILIA

Mucus traps microorganisms and prevents them from reaching and colonizing the

mucosal epithelium. Mucus also contains lysozyme to degrade bacterial peptidoglycan,

an antibody called secretory IgA that prevents microbes from attaching to mucosal cells

and traps them in the mucus, lactoferrin to bind iron and keep it from from being used by

microbes, and lactoperoxidase to generate toxic superoxide radicals that kill microbes.

Cilia on the surface of the epithelial cells propels mucus and trapped microbes upwards

towards the throat where it is swallowed and the microbes are killed in the stomach. This

is sometimes called the tracheal toilet.

B. THE COUGHING AND SNEEZING

Remove trapped microbes

C. VOMMITING AND DIARRHEA

Removing pathogen and toxin in gastrointestinal tract

D. PHYSICAL FLUSHING ACTION OF BODY FLUID

Fluids such as urine, tears, saliva, perspiration, and blood from injured blood vessels also

flush microbes from the body

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Conclusion

Recognition of these molecular structures allows the immune system to distinguish infectious

nonself from non-infectious self. All of these specialized cells and parts of the immune system

offer the body protection against disease. For instance, biotechnology provides to vary unlimited

type of artificial antibody to help a person with weak immune system. Although immune system

disorders usually can't be prevented, you can help your child's immune system stay stronger and

fight illnesses by staying informed about your health’s condition and working closely with your 

doctor.

References

1. http://kidshealth.org/parent/general/body_basics/immune.html# Accessed on

27thSept2011

2. http://pathmicro.med.sc.edu/ghaffar/innate.htm Accessed on 27thSept2011

3. http://www.arthritis.org/innate-immunity.php Accessed on 27thSept2011

4. http://www.bio.davidson.edu/people/sosarafova/Assets/Bio307/emrivard/Innate

%20Immune%20Response.html Accessed on 28thSept2011

5. http://sprojects.mmi.mcgill.ca/immunology/cell_non_spec.htm Accessed on 28thSept2011

6. http://textbookofbacteriology.net/innate_2.html Accessed on 28thSept2011

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Appendices

Leukocyte

 dendritic cell has engulfed some mycabacterium (M) with

are residing within vacuoles (CHV).