Immune System: Diseases, Disorders & Function.

Pedro_P

T-cells attacking a cancer cell.
▼ The role of the immune system — a collection of structures and processes within the body — is to protect against disease or other potentially damaging foreign bodies. When functioning properly, the immune system identifies a variety of threats, including viruses, bacteria and parasites, and distinguishes them from the body's own healthy tissue, according to Merck Manuals.
Innate vs. adaptive immunity
The immune system can be broadly sorted into categories: innate immunity and adaptive immunity.undefined
Innate immunity is the immune system you're born with, and mainly consists of barriers on and in the body that keep foreign threats out, according to the National Library  of Medicine(NLM). Components of innate immunity include skin, stomach acid, enzymes found in tears and skin oils, mucus and the cough reflex. There are also chemical components of innate immunity, including substances called interferon and interleukin-1.
Innate immunity is non-specific, meaning it doesn't protect against any specific threats.
Adaptive, or acquired, immunity targets specific threats to the body, according to the NLM. Adaptive immunity is more complex than innate immunity, according to The  Biology Project at The University of Arizona. In adaptive immunity, the threat must be processed and recognized by the body, and then the immune system creates antibodies specifically designed to the threat. After the threat is neutralized, the adaptive immune system "remembers" it, which makes future responses to the same germ more efficient.
Major components
Lymph nodes:Small, bean-shaped structures that produce and store cells that fight infection and disease and are part of the  lymphatic system— which consists of bone marrow, spleen, thymus and lymph nodes, according to "A Practical Guide To Clinical Medicine" from the University of California  San Diego(UCSD). Lymph nodes also contain lymph, the clear fluid that carries those cells to different parts of the body. When the body is fighting infection, lymph nodes can become enlarged and feel sore.
Spleen:The largest lymphatic organ in the body, which is on your left side, under your ribs and above your stomach, contains white blood cells that fight infection or disease. According to the National Institutes of Health(NIH), the spleenalso helps control the amount of blood in the body and disposes of old or damaged blood cells.
Bone marrow:The yellow tissue in the center of the bones produces white blood cells. This spongy tissue inside some bones, such as the hip and thigh bones, contains immature cells, called stem cells, according to the NIH. Stem cells, especially embryonic stem cells, which are derived from eggs fertilized in vitro (outside of the body), are prized for their flexibility in being able to morph into any human cell.
Lymphocytes:These small white blood cells play a large role in defending the body against disease, according to the Mayo Clinic. The two types of lymphocytes are B-cells, which make antibodies that attack bacteria and toxins, and T-cells, which help destroy infected or cancerous cells. Killer T-cells are a subgroup of T-cells that kill cells that are infected with viruses and other pathogens or are otherwise damaged. Helper T-cells help determine which immune responses the body makes to a particular pathogen.
Thymus:This small organ is where T-cells mature. This often-overlooked part of the immune system, which is situated beneath the breastbone (and is shaped like a thyme leaf, hence the name), can trigger or maintain the production of antibodies that can result in muscle weakness, the Mayo Clinic said. Interestingly, the thymusis somewhat large in infants, grows until puberty, then starts to slowly shrink and become replaced by fat with age, according to the National Institute of Neurological Disorders and Stroke.
Leukocytes:These disease-fighting white blood cellsidentify and eliminate pathogens and are the second arm of the innate immune system. A high white blood cell count is referred to as leukocytosis, according to the Mayo Clinic. The innate leukocytes include phagocytes (macrophages, neutrophils and dendritic cells), mast cells, eosinophils and basophils.
Diseases of the immune system (▪ ▪ ▪)

► Please, read the full note here: Source