Dr. Sinan Bahjat Issa M B Ch B, M Sc, F I B M S The Immune system Dr. Sinan Bahjat Issa M B Ch B, M Sc, F I B M S

The main function of the immune system in our bodies is to prevent or limit infections (by bacteria, fungi, viruses, and parasites) and fight diseases. 

Our immunity is composed of two arms: the Natural (or Innate) arm and the Acquired (or adaptive) arm.

The Innate immunity is considered as the first and second lines of defense against foreign subjects in our body, while the adaptive immunity is the third line of defense.

Innate Immunity

The first line of the Innate immune system is the physical and the mechanical barriers (e.g. skin, the mucous membranes, the secretions, and the normal flora).

The second line consists of: phagocytic cells (i.e. granulocytes, macrophages, natural killer cells, and dendritic cells).

Inflammation; which is one of the important mechanisms of defense against diseases.

Fever; which can change the environment of the invading microorganisms.

Protective proteins; like the complement system proteins and interferons.

Natural killer cells; which are non- specified lymphocytes that can attack the non- self subjects.

The Innate immune system has the ability to distinguish between non- self antigens (i.e. proteins that can elicit an immune response) which can invade the body from our self antigens.

The process by which the Innate immune system can do so is through specific receptors called Pattern Recognition Receptors (PRR).

On the other hand, some parts of our bodies are hidden “i. e On the other hand, some parts of our bodies are hidden “i.e. sequestered” to our immune system. The body will consider them as “non- self” antigens as soon as it will be discovered.

These parts are: the brain, the eye lenses, and the sperms.

The Innate immune system is consisting of the humoral and the cellular components.

Humoral immunity is so named because it involves substances that are found in the humors, or body fluids (e.g. the complement proteins).

The cellular elements of the Innate immunity are the Phagocytes (i. e The cellular elements of the Innate immunity are the Phagocytes (i.e. neutrophils) and Natural Killer cells.

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