Immunology Disorders
The immune system is responsible for protecting the body from various parasites, bacteria, virus etc. that try to destabilize the homeostasis. Naturally, the immune system is considered one of the most important mechanisms that help us recuperate from diseases. When the immune system malfunctions and starts destroying self-cells, it leads to certain disorders. In other circumstances, the immune system may be suppressed and fail to kill disease causing cells. Here we will discuss a few disorders of the immune system.
HYPERSENSITIVITY TYPE I
Allergy or hypersensitivity type I is also known as allergic reaction or intolerance, in this scenario the immune system creates a response to apparently non harmful allergens. In this type of hypersensitivity, the antigen is first presented to CD4+ cells, which in turn activate the B cells to create the IgE antibodies specific to the antigen (allergen). After the first exposure to allergens the IgE binds to the surface of mast cells and basophils (White blood cells). These IgE coated cells are sensitized to a particular allergen. When the body is exposed to the allergen for a second time, the IgE binds to the allergen and causes granulation along with the release of histamine, leukotriene and prostaglandin, which affect the surrounding cells. The symptoms of type I hypersensitivity reactions are characterized by vasodilation and smooth muscle spasms. Anaphylaxis may happen if the entire body is involved in the allergic reaction. Antihistamines, and corticosteroids are used to control the Hypersensitivity type I reactions. Some common allergens are pollens, chemicals, dust etc. when a person is exposed to such allergens, immediately the hypersensitivity type I reaction starts.
HYPERSENSITIVITY TYPE II
In the hypersensitivity type II reaction, the antibody IgG and IgM bind to antigen presented on the host cell and perceives it as a foreign body. Therefore the antigen-antibody complex kills self-cells by the creation of Complement Membrane Attack Complex, which acts by rupturing through the cell membrane leading to cell lysis. When the antibodies IgG and IgM start killing the patient’s own cells then this gives rise to an immune disorder. For example in autoimmune hemolytic anemia, the antibodies start targeting red blood cells which leads to massive loss in RBCs and reduction in lifespan of RBC from 120 days to a few days. Autoimmune hemolytic anemia is a rare condition but it may affect patients who have just received blood transfusion. Another example of immune disorder resulting from hypersensitivity II is rheumatic fever where antibody cross reactivity causes hypersensitivity type II reaction directed at peri-arteriolar connective tissue.
HYPERSENSITIVITY TYPE III
Type III hypersensitivity reaction occurs as a result of incomplete destruction and subsequent accumulation of antigen-antibody complexes. This type of hypersensitivity reaction is characterized by inflammation. Sometimes the IgG antibodies bind to soluble antigens that form a circulating immune complex of antigen and antibody. This antigen-antibody complexes may get deposited on the walls of blood vessels and trigger an inflammatory response. Some examples of such immune disorders are rheumatoid arthritis, serum sickness etc.
HYPERSENSITIVITY TYPE IV
Hypersensitivity type IV is a cell mediated delayed immune response that involves the CD4+ T Cells. The T cells recognize a complex formed between antigen and class 2 MHC (Major Histocompatibility Complex). The antigen presenting cells are macrophages which secrete the Interleukin-12 on activation (second exposure) and elicit an inflammatory response due to the hydrolytic enzymes that kills all surrounding cells. If the pathogens are intracellular in nature, macrophages form multinucleated giant cells. The T-cell mediated pathway involves the activation of IL-2 and interferon gamma that results in creation of cytokines and CD8+ T cells that kill target cells on contact. Examples of disorders associated with hypersensitivity type IV are Diabetes mellitus type I, which occurs when the insulin creating beta cells of the pancreas are the victims of an autoimmune hypersensitivity type IV reaction. Other examples are Rheumatoid arthritis, and multiple sclerosis where the antigen in synovial membranes, and oligodendrocyte proteins are target respectively.
IMMUNODEFICIENCY
Certain immune disorders can stem from the inability of the immune system to elicit an appropriate response to a threat. Immunodeficiency disorders prevent the body from fighting infections and diseases with adequate potency and makes patients more susceptible to bacterial and viral infections. Immunodeficiency disorders can be congenital (example, Alymphocytosis) or acquired (example, AIDS, cancer of immune system). Congenital immunodeficiency disorders are present in children from birth. Children affected by primary or congenital immunodeficiency must lead a very careful lifestyle as the immune system is incapable of defending the body from infections. On the other hand, secondary or acquired immunodeficiency disorders are a result of exposure to certain chemicals or disease that inhibits the immune system from functioning to its full ability. Patients suffering from chronic lymphocytic leukemia a cancer of the lymph gland that affects white blood cells and thereby causes immunosuppression. Patients who had their spleen removed due to some infection, HIV infected individuals, cancer patients undergoing chemotherapy are prone to immunodeficiency disorder. Such disorders are diagnosed by T cell and white blood cell count. Patients suffering from immunodeficiency are treated through antibiotics treatments and antibody replacement. Interferons are also prescribed to treat viral infections in immunocompromised patients.
CANCER
Immune suppression involved in cancer and tumor progression is mediated by tumor-derived soluble factors (TDSFs) like Interleukin-10 (IL-10), transforming Growth Factors-β (TGF- β, and Vascular Endothelial Growth Factor (VEGF). Usually cancerous cells may get killed by the cells of the immune system, but in immunocompromised individuals the cancer cells may grow uninhibited thus increasing chances of skin cancer. Tumor cells often exert immune suppression on the immune system’s tumor response. Dendritic cells present tumor antigens to both B cell and T cells, on the other hand tumor cells attack the dendritic cells. They also stop T cells from reaching the tumor site by creating an effective block at vascular endothelium that the tumor-reactive T cells are unable to cross(Motz and Coukos). The T cells that manage to cross the endothelial barrier are presented with a maze of tumor stroma that they must navigate to reach the target tumor cells. Finally, when the T cells reach the target cells they are presented with other immunosuppressive factors that prevent tumor cell recognition and attack. In some cases tumor cells down-regulate antigen presentation therefore inhibiting binding of T cells altogether.
It has been found that patients of organ transplants and AIDS patients who are usually immunocompromised are at a higher risk of getting skin cancer. Sometimes individuals exposed to extreme chemotherapy become immunocompromised and are at a higher risk of getting melanocarcinoma.
Works Cited
Motz, Greg T, and George Coukos. “Deciphering and Reversing Tumor Immune Suppression.” Immunity 39.1 (2013): 61–73. Print.
