In higher vertebrates, the immune system can distinguish self-cells and non-self. If this property is lost due to genetic abnormality and it attacks self-cells, then it leads to

The immune system of higher vertebrates, including humans, is capable of distinguishing between self-cells and non-self cells. When the immune system encounters a non-self antigen, such as a pathogen or an antigen from a transplanted tissue, it mounts an immune response to eliminate the foreign invader. However, in some individuals, the immune system fails to recognise self-antigens as ‘self’ and mounts an immune response
against normal body cells. This leads to the development of autoimmune diseases, which are characterised by inflammation and damage to the affected tissues or organs. Examples of autoimmune diseases include type 1 diabetes, rheumatoid arthritis, lupus, multiple sclerosis etc. 

(2) Active immunity is the immune response generated by the individual’s own immune system in response to
antigenic stimulus. It is induced by a vaccine or a natural infection.

(3) Allergic response is an exaggerated immune response to allergens, such as pollen or certain foods.

(4) Graft rejection refers to the immune response mounted by the recipient’s immune system against a transplanted organ or tissue that is recognised as ‘non-self’.