The Immune System: Our Army Against Disease.

The immune system is a set of structures, cells or biological processes of the body that is responsible for protecting us from external and internal aggressions that are dangerous to our health.

There are two types of immunities:

• The innate.
• The acquired.

The attacks can be physical attacks, of a biological nature, such as bacteria, which we call pathogens, of a physical-chemical nature, or they can be internal attacks, such as cancer.

What is the immune system?

It is a complex system that is made up of different fluids, tissues, and organs. These are found mainly in the skin, bone marrow, blood, thymus, lymphatic system, spleen and mucous membranes.

We are going to focus on the bone marrow and the cells it generates, which are specialized in immune function. All the cells that are synthesized here are transported through the body thanks to the blood and lymphatic system.

Therefore, the cells that are generated in the marrow and that will defend us from possible dangers are:

• Neutrophils.
• Eosinophils.
• Basophils.
• Monocytes
• Dendritic cells.
• Mast cells.
• Macrophages

Neutrophils in the immune system

Neutrophils are a type of white blood cell, but what are white blood cells ? Leukocytes are the famous white blood cells that are part of the different cells that are part of the blood. They are the executors of the immune response.

Neutrophils are the most abundant leukocytes in the blood, representing between 60 and 70% of them. The main function of these cells is to phagocytose, that is, to capture or digest bacteria and fungi.

When an acute onset of inflammation develops in a bacterial infection, they are among the first cells to arrive, being the main components of pus.

Eosinophils

Eosinophils are also a type of leukocyte that is responsible for phagocytosing antigen-antibody complexes. In order to perform their phagocytic function, they surround the target with their cytoplasmic membrane and disintegrate it. They are more effective in infections developed by parasites.

These cells provide us with an immediate defense against aggressions, but they do not give us long-term immunity. They are also important mediators in terms of processes such as allergy or asthma. They can intervene in the allergic response and in hypersensitivity reactions. They do this because they have the ability to neutralize histamine.

What do we know about basophils?

They are also leukocytes but they are the least abundant in the blood. Basophils are the cells that initiate allergic processes as they release histamine, serotonin in low concentrations, and other chemicals.

Basophils, in addition to other substances, have immunoglobulin receptors inside them, which are structures related to allergies, and that is why they are related to this process.

What about monocytes?

These cells are also white blood cells that, like many others, are phagocytic, that is, their main function is to engulf different microorganisms or cell debris in order to prevent infections and diseases.

The dendritic cells

This type of cell is known for being antigen presenting cells, whose function in the immune system is to capture, process and present antigens on their membranes so that they can be destroyed.

Normally, they usually present antigens to T lymphocytes. This interaction between dendritic cells and T lymphocytes initiates antigenic immune responses.

On the other hand, T lymphocytes are another type of cell of the immune system, being of vital importance in the adaptive immune system. It is characterized because its response is specific for each antigen, a fundamental difference with the innate immune system, which protects us from infectious processes in a non-specific way.

What are mast cells?

In the immune system we can also find this type of cells, which are part of the connective tissue (a heterogeneous set of tissues that have a common origin, the embryonic mesenchyme) and which are also known as mast cells.

Like the others, they are formed in the bone marrow, from stem cells and act in inflammatory and allergic processes. They are distributed in many tissues of our body.

They have the ability to synthesize and create histamine and heparin (anticoagulant substance) mainly. To carry out their function they must be activated. Once activated, they release the content of the granules they have inside. This process is known in immunology as mast cell degranulation.

The role of macrophages in the immune system

Finally we have macrophages, phagocytic cells responsible for detecting, engulfing and destroying pathogens and apoptotic cells. Macrophages are formed from the differentiation of monocytes.

These cells play a fundamental role in the immune system, as they alert to the presence of invading substances or microorganisms. In addition to this role, they have different functions such as:

• Phagocytosis
• Inflammation.
• Presentation of antigens.
• Tissue repair.
• Haemostasis