Our skin is being commonplace to microorganisms. Few microorganisms are an asset to our body, but most microorganisms invade our body, leaving us vulnerable. If microorganisms weaken our body, it is difficult for our body to defend itself. So we have to avert it. In order to achieve this, the human body has a guarding system for these harmful microbes called the immune system.
Immune system:
Two types of immunity occur in the human body.
Innate immunity: It is a type of non-specific immunity. It consists of the first and second lines of defence against pathogens.
Adaptive immunity: It has a specific reaction toward pathogens. It acts as the third line of defence against pathogens.
The first line of defence (Innate):
Skin is the first component of the immune system and prevents the infiltration of microbes into our bodies. The mucosal lining traps the microbes. These act as the physical barrier of the human body. Lysozymes secreted in the eyes and acid in the stomach act as the chemical barriers of the human body. The genitourinary and urinary tract have their microbial community; these compete with intruders and act as barriers.
The second line of defence (Innate):
The second line of defence is inflammation. It is done by mast cells. If the pathogens get into our body, mast cells produce a chemical signal called histamine that alerts our white blood cells (WBC), red blood cells (RBC), and thrombocytes (platelets). If it is a harmless intruder, our immune system reacts to that intruder. Leukocytes (WBC) have all access to pass through the body except the brain and spinal cord. It is like the VIP of the human body. Leukocytes appeared in many types. It mainly has a phagocytic activity that engulfs the pathogens through phagocytic cells. Phagocytic cells patrol our body and kill the infectious cell and die, leading to pus formation and neutrophils. Another large cell called macrophages (matured monocytes) performs phagocytosis. These cells engulf one hundred pathogens and die. It also detects cancerous cells and kills them too. Macrophages are found on tissues, whereas monocytes are found on blood.
Natural killer cells:
Meanwhile, natural killer cells(NK cells) can efficiently detect when our cells have gone infected with pathogens. NK cells detect a protein called major histocompatibility (MHC) produced by normal cells. Abnormal cells do not produce so, the NK cells detect the abnormal cells and destroy them.
Dendritic cells:
Dendritic cells are found in exposing organs like the nose and lungs. It creates the link between innate adaptive immune systems. Dendritic cells kill the pathogens and collect the information about them in the form of antigen and give it to the adaptive immune system. Antigen(Ag) is a trace of pathogens that leaves around. Ag can be found on the surface of the pathogens detected by the immune system for recognition. However, dendritic cells and macrophages cells kill the pathogens and gather the details of an antigen of those pathogens, and then these details pass on to our T cells.
The third line of defence (Adaptive immunity):
Adaptive immunity efficiently identifies and differentiate the pathogens. It consists of two cells, B lymphocyte (B cell) and T lymphocyte (T cell). T cells arrive when an infection has already appeared. It is called cell-mediated immune responses, while B cells arrive when the pathogens enter but have not yet caused any disease. It is called a humoral immune response.
T lymphocyte:
It has two types:
1.T helper cells (TH cells)
2.Cytotoxic T cells (TC cells).
It forms effector T-cells that circulate through the blood and alert the WBC. Memory t cells keep the record of the antigen for future reference. Cytotoxic T cells perform when our organs or cells get heavily infected with pathogens, and the cytotoxic T cells kill those infected dying cells.
B lymphocytes:
It produces chemicals called antibodies which fit on the antigen present on the surface of pathogens like lock and key mechanisms. These antibodies around the pathogens act like tags. They signal to the macrophages to come and kill the pathogens. It also makes memory B cells when B cells encounter the antigens. So the B and T memory lymphocytes have the record of all encountered pathogens.
Furthermore, they strengthen our body’s immune responses. So the next time we get an infection, the immune system recognizes it, and we will not get sick. The same thing is used in vaccines. Innate immunity takes action against pathogens within a few hours, while adaptive immunity takes hours to months.
Now we will see what the ways our body gets immunized are. Adaptive immunity is broken into two types,
1.Active immunization
2.Passive immunization
Active immunization is to infect the body and get the antibodies for immunological responses. Active immunity stays for the long term to a lifetime. These are two types,
Natural immunity:
If the person gets the disease and gets over it, that person-specific immunological response towards that particular infectious pathogens vaccine-induced immunity is called Active artificial immunity. Vaccines are produced by the inactive or dead strains of pathogens that will induce the human body’s immune responses.
Passive immunity is to get immunity by injecting antibodies and staying for the short to long term. So it has two types of immunity.
Artificial passive immunity:
The antibodies derived from the different personalities are experimentally injected into the infected person to get the specific immunity towards the infection.
Natural passive immunity (via maternal):
The newborn babies get antibodies from the mother to survive from the pathogens.
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