Cells of the immune system are responsible for the maintenance of the immune reactivity of the organism against penetrating viral and bacterial pathogens in the human body, which sometimes can cause dangerous health infections. Initially, the circuit is driven by the production of pluripotent stem cells that differentiate and give rise to clones of B-and T-cell lymphocytes, neutrophils, eosinophils, basophils, monocytes, dendritic cells, mast cells and red blood cells.

Neutrophils are a special type of immune system cells, which are differentiated from myeloid stem cells. They migrate into the bloodstream at himiotaksichen signal from the body. By way of specific Fc-receptor fixed opsonized by the complement system and pathogen invasion within particles. They have the ability to destroy pathogens directly emptied by the strong bactericide them.

Eosinophils are another type of special cells of the immune system. These granules have a strong cytotoxicity to the endothelium, epidermis, neuronal cells and proteins. Their main function is to synthesize mediators and cytokines.

Basophil cells and mast cells contain receptors for immunoglobulin E. Their main function is to synthesize prostaglandins Class 2. They also provide protection against parasites come against immunoglobulin E-mediated allergic reactions. In this way, the body remains secure during falling of animal parasites in the food, which is particularly common in the consumption of food or poorly cleaned poorly processed meat products.

Monocytes have a cytoplasm filled with specific granules. They originate from myeloid stem cells and differentiate into macrophages. Their main function is to phagocytose emptied environmental pathogenic microorganisms. These processes are carried out after activation by interferon or TNF, macrophages subsequently acquire strong cytotoxic activity and have a strong bactericidal effect against pathogens become trapped in the body.

Dendritic cells are antigen presenting cells. They can migrate into the blood and lymph. They are activated by irritation of those who fell in the human pathogenic microorganisms. The next stage of their operation is not present on its surface MHC molecules of the system that is the major histocompatibility complex on. Also involved in the activation of clusters of differentiation in the body - CD-cells.

T lymphocytes very well may be defined as "the heads of special operations to eliminate the invasion and destruction of pathogenic microorganisms." They are produced in the bone marrow pluripotent stem cells and then migrate to the thymus and mature there. Subsequently differentiate and acquire the specific T-cell reactivity - TCR.

Accordingly, this type of cells are involved in the differentiation to a CD- cells , which are clusters of differentiation. CD4 + T - cell specific agents have adjuvant - inducing function . They give rise to a whole new spot in the production of protective cells against emptied into a person's body pathogenic microorganisms. CD8 + T-cell lymphocytes are the next most important clusters that need to be addressed. They have strong cytotoxic and suppressor role. Cast directly to the differentiation of killer cells and suppressor cells when the body is facing the threat of invasive blood-borne viruses and bacteria.

The role of the immune system is to protect the body against foreign antigens, and do not react to cause outbreaks of disease events in the human body. They also prevent the occurrence of cross-reactions between antigens and the invasion of the body's own antigens. That function of the immune system is performed by the T-cells that acquire the ability to execute it in the thymus after three-step reactions.

- The first step is differentiation of a double negative T cell lymphocytes. These are CD4-and CD8-cells.
- The second stage is the occurrence of double positive cells - to develop CD4 + and CD8 + cells.
- The third stage is the mixed cells, where they meet a single positive and single negative T-lymphocytes. There are two possible combinations. The first one is the manifestation of CD4-and CD8 + cells, and the second expression of CD4 + and CD8-cells.

B-cell lymphocytes are another important cellular arm of the immune reactivity of the organism against environmental emptied the invasion of microorganisms. They are involved in humoral immunity by synthesis of antibodies. Each mature B lymphocyte produces only one type specific antibody that is expressed on the surface, such as a B cell receptor. Antibodies react against the onset of the invasion antigens.

NK-cells are a specific cell type. They can be defined as "a SWAT team to fight pathogens." Their name comes from the abbreviation natural killers, which means that they kill directly taken into the body microorganisms without subjecting them to any attempts to phagocytic or neutralization. NK-cells are most pronounced cytotoxicity compared with all other members of the immune response. Thus limiting the spread of virus-infected cells in the human body.