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A autoimmune disease
Immunity refers to the overall ability of the host to fight the pathogens. This is a function of our immune system. Our immune system consists of lymphoid organs, tissues, cells and antibodies which provide immunity.
There are two types of immunity, innate immunity and acquired immunity. Innate immunity is nonspecific and present since birth.
Acquired immunity is the immunity that an individual acquires during his/her lifetime and is of two types: active immunity and passive immunity.
In active immunity, a person’s immune system produces antibodies either in response to an infection or vaccination.
Passive immunity is the immunity that an individual acquires by receiving antibodies from another immune individual. For example, a child receives IgA antibodies from the mother through colostrum (The first milk produced by the mother).
But unfortunately, it has been noticed that sometimes either due to genetic factors or other unknown reasons, the immune system goes haywire and attacks the body's self-cells and destroys them. Self-cells refer to the body’s own cells to which the immune system, under ideal and normal conditions, should not react. This is known as autoimmunity and the diseases that result are known as auto-immune diseases.
Example: Rheumatoid Arthritis
In this auto-immune disorder, the immune cells attack cells of the synovial joints. This leads to swollen inflamed joints and bone erosion. All of these leads to difficulty in moving the joint.
Certain individuals are sensitive to some particles in the environment and display symptoms like sneezing and wheezing. These are called allergic responses.
The exaggerated response of the immune system to certain foreign substances called allergens is called allergy. The various allergens include mites in dust, pollen, and animal dander present in the environment.