The immune system comprises a great set of molecules, cells, tissues and organs that realize immune reactions. It consists of numerous subsets working as a united cooperative cross-linked community.
- Immunity is the function of the immune system.
- Organs that make the major barriers in the immune system of the body include skin, mucous membrane, stomach acid, useful bacterias etc. Also, the reflexes that cause to cough and sneeze include the removal of foreign particles ie. germs etc.
There are the following subsets within the immune system on the cellular and molecular levels of biological organization.
The lymphoid sub-system includes the cells synthesizing specific factors of immune defence – antibodies (Abs) and T cell antigen-binding receptors (TCR).
One more sub-system comprises humoral factors of innate (non-specific) immunity.
Also, there are:
1. Mononuclear phagocyte system (MPS)-
- It is defined as a network of cells that has a number of functional features including movement towards the signalling molecules such as cytokines, engulf or digest the microscopic particles like the bacteria, virus or other pathogens, present antigens to the adaptive immune system and exhibit cytotoxic activity.
- It also comprises of monocytes, macrophages, and dendritic cells
2. Dendritic cell system
- Dendritic cells are antigen-presenting cells which is able to induce naïve T cell activation and effector differentiation
- They are identified with the presence of major histocompatibility complex (MHC) class II molecules (MHC-II) and of CD11c.
3. Granulocyte system
- Granulocyte system is comprised of neutrophil, basophil and eosinophil leukocytes
- Neutrophils and eosinophils are phagocytic in nature while basophils are non- phagocytic leukocytes serving for allergic responses.
- Neutrophils are present vast in number and are thus the first leukocytes to reach the infection site.
4. Natural killer (NK) cells system
- NK cells large-size lymphocytes play a protective role in ensuring the lysis of cancer or virus-infected target cells regardless of their antigenic specificity (so-called non-immune cytolysis).
- It consists of a great number of azurophilic granules in the cytoplasm.
5. Complement system
- Complement is a system of enzymes and proteins contributing to the lysis of target cells.
- The complement system includes serum and membrane-bound proteins that function in both specific and non-specific immune reactions.
- They are activated via a chain of proteolytic cascades.
6. Platelet system.
- Platelets are tiny blood cells that help blood clotting
- Platelets move into the site of the injury and they stick to one another and that also releases chemical signals to attract more platelets forming aggregation.
All of these sub-systems with exception of lymphoid one participate in immune reactions via a non-specific mode of action. The lymphoid system comprising T and B cells produces specific molecules of the immune response.