In view of the last topic, today I would like to talk briefly about the human immune system.
Simply speaking, the human immune system is like a wall, when there are external pathogens, such as bacteria, proteins, viruses, molds, etc. into the human body, we will erect this barrier to help us fight foreign substances. Usually, our first wall will be the skin, after all, the skin can become the outermost barrier of the body.
Specific/non-specific immunity
The human immune system can be subdivided into “non-specific immunity” and “specific immunity“.
Non-specific immunity is also called “innate immunity“. As the name implies, it does not target specific invading pathogens, but rather blocks them as long as the invader is not an autologous cell or a product of an autologous cell. Non-specific immunity constitutes our basic defense system.
Specific immunity, also called “acquired immunity“, is the ability to recognize and remember pathogens once they invade the body, and to activate defense mechanisms. In particular, acquired immunity has three main characteristics: 1. specificity: different antibodies recognize different antigens, 2. memory: remembering the characteristics of antigens and responding quickly next time, and 3. recognition: good at distinguishing between enemies and self, not harming oneself.
The cells of innate immunity are NK cells, granulocytes and macrophages as the main immune cell groups. Although they are capable of comprehensive germ elimination, their ability to do so is limited. Acquired immunity is based on B cells, T cells and dendritic cells, with B cells producing antibodies, T cells removing pathogens and cancer cells, and dendritic cells phagocytosing antigens and presenting antigens.
Immune organs
Where do these immune cells come from? The human immune organs can be divided into central and peripheral immune organs. The central immune organs include the thymus and bone marrow, where B cells are produced from the bone marrow, and T cells are produced from the thymus. The peripheral immune organs include the spleen, lymph nodes, mucous membranes and lymphatic-related tissues, and the skin. The following is a more detailed description of these immune cells.
Immune cells
Immune cells derived from stem cells can be divided into lymphocytes and granulocytes. Under lymphocytes, there are B cells, T cells and NK cells. Granulocytes contain monocytes, neutrophils, basophils, eosinophils and mast cells. The B cells can be subdivided into memory cells and plasma cells; monocytes can develop into dendritic cells and macrophages.
Let us now introduce these cells.
Neutrophils: 60-70 % of white blood cells are in the majority. Neutrophils have the ability to metamorphose and phagocytose, and are very important in fighting diseases and protecting the body.
Eosinophils: Eosinophils increase when the body is infected with parasites. Their phagocytic capacity is not as good as that of neutrophils and their main function is to regulate allergic reactions.
Basophils: It is a cell that promotes inflammatory responses in many immune responses and is associated with allergic diseases such as anaphylaxis, allergic rhinitis, asthma, and atopic dermatitis.
Macrophage: Monocytes change from monocytes to macrophages as soon as a foreign enemy invades, and macrophages are important cells in non-specific immunity that are always on patrol for foreign invasion.
Dendritic cell: Its most vital function is to process and present antigens to T cells of the immune system, so it is an antigen-presenting cell.
Natural killer cell: The natural killer cells specialize in dividing tumor cells by releasing Perforin, which punches holes on the cells, and Granzyme B, which causes the cells to kill themselves.
Plasma cell: Derived from B cells, the primary function is to produce antibodies
Memory cell: It is differentiated from B cells to remember the invader antigen for a rapid response the next time it is encountered.
First vaccine
Last but not least, the first vaccine was invented by Dr. Edward Jenner in England in 1796. Jenner observed that milkmaids would not catch smallpox, so he inoculated children with cowpox pus and successfully made them immune to smallpox.
The above is a brief introduction to the human immune system, if you want to have a more in-depth and more understanding of immunity, you can refer to the previous topic:
References:
Johns Hopkins Medicine: The Immune System 🔗
Nicholson LB. The immune system. Essays Biochem. 2016;60(3):275-301. doi:10.1042/EBC20160017 🔗
