Which disease is fought by the immune system as part of its function to recognize and remove abnormal "self" cells?

The correct answer to the question is: Cancer.

Explanation:

Cancer is a disease condition in which some cells of an organism fails to regulate, control and maintain their metabolism, cell cycle, structure and function and grow uncontrollably.There can be many reasons due to which a cell fails to carry out a  normal cycle. Some are listed below:Genetic predisposition from parents.Uncontrolled activation of a Proto-oncogenes. Oncogenes are those which on activation can promote the unregulated growth of cells.Inactivation of the Tumour suppressor gene. Tumour suppressor genes helps to keep the cell metabolism, function and cell cycle under control.Cancer promoting mutations.Influence of carcinogenic agents. Carcinogenic agents are those that can induce cancer.In the initial period of oncogenesis (development of cancer), the cells which are undergoing unregulated cell divisions are recognised by the immune cells as foreign and they try to kill and destroy these cells to prevent them from causing cancer.