Immunity is protection against diseases, and it involves various activities of the immune system. We can distinguish between innate immunity which is present from birth, and acquired (adoptive) immunity, which develops through exposure to exogenous factors like invasion of bacteria, viruses or parasites.
Immune system is a collection of cells and proteins which work to provide protection to the body from harmful microorganisms, such as bacteria, viruses, and fungi.
The innate immunity, present from birth, is the nonspecific first line of defence against foreign pathogens, is an integral part of the immune response. It is mediated by dendritic cells (DCs), natural killer cells (NK), macrophages, neutrophils, basophils, eosinophils, and mast cells. It also includes antibodies, or immunoglobulins, also called the protective proteins, which have been inherited by a child. Additional natural defence mechanisms include the skin, mucous membranes that line the mouth, throat, nose, and intestine. If microorganisms manage to penetrate these natural defence barriers, the white blood cells, mentioned above, go into action. Another defence mechanism include some naturally produced substances, such as interferon, or a blood proteins called the complement system, which jog is to destroy the invading pathogens.
The adoptive immunity acts as a second line of defence when the body’s innate defences failed. The adaptive immune system responds in a specific way to each type of invading pathogens, and retains a memory of the pathogen so that defence mechanisms can be used is the future too. The adaptive immune system must recognize the invading pathogen as an antigen, a foreign body. Next, one out of two immune responses is provided against the foreign body; humoral or cellular. The first one plays important role in the defence against bacteria; where after s complex process, certain B-lymphocytes will multiply and produce a large number of antibodies to bind to antigens. The pathogens bearing the antigens will be neutralized by white cells called phagocytes in the process of phagocytosis. This process, then may activate complement system, which in turns, increases the efficiency of thee phagocytosis.
Cellular immunity plays a vital role in the defence against viruses and some types of parasites which hide within cells. The defence mechanism involves two types of T-lymphocyte: helper cells to recognize the antigens, and activate the killer cells to destroy the cells that have been invaded.
There are many disorders that involve immune system, among which are immunodeficiency disorders (primary: the ones we are born with, and acquired, called secondary), autoimmune disorders, allergies, and in fact most of the illnesses become chronic due to the weakness of this system, therefore it is vital to improve and keep it to the best possible condition in order for it to be able to provide the best possible line of defence against pathogens.