A group of cells obtained from a multicellular organisms like mouse,rat,horse or even human beings,which would not divide and grow in normal circumstances in a particular culture medium conditions indefinitely but due to certain changes like mutations or infected by a virus can keep growing continuously if the specific conditions for its divisions and subsequent growth are satisfied. Thus they can be grown in in vitro.
They are an important tool for research in fields like biochemistry, molecular biology, cell biology, biotechnology etc.
An immortal cell line should not be confused with stem cell which can also divide indefinitely but form a normal part of development of a multicellular organism.
One such example of an immortal cell line is that of HeLa cells-one of the oldest, commonly used and an extremely popular human cell line isolated from a cervical cancer cells of the patient named 'Henrietta Lacks'.The HeLa strain of cells were used to develop polio vaccine by Jonas Salk.
They have also been used by scientists around the world for research studies in AIDS, cancer,to know the effects of radiation and toxic substances,gene mapping ,testing the human sensitivity to cosmetics ,glue and many other such products.
The secret behind the immortality of HeLa cells is that since the cells were infected by Human Papilloma Virus(HPV-18), it attained immortality as the virus uses the host's biochemical machinery for replication of DNA copies and thus alters the normal cells functioning.
The real-life story behind the family of Henrietta Lacks and the woman herself ,the racial injustice caused to the family as she was a poor,black tobacco farmer and the ignorance towards them by the world is aptly described in a non-fictitious book named "The Immortal Life of Henrietta Lacks" authored by 'Rebecca Skloot'.
Publisher- 1st published by Crown Publishers (2010). The 2011 edition published by Pan Books,an imprint of Pan Macmillan, a division of Macmillan Publishers Limited.
Excerpts from the book- (Part three-Immortality 27. The Secret of Immortality 1984-1995 Page no-248)
"...By the early nineties ,a scientist at Yale had used HeLa to discover that human cancer cells contain an enzyme called telomerase that rebuild their telomeres.The presence of telomerase meant cells could keep regenerating their telomeres indefinitely. This explained the mechanics of HeLa's immortality: telomerase constantly rewound the ticking clock at the end of Henrietta's chromosomes so they never grew old and never died.It was this immortality, and the strength with which Henrietta's cells grew ,that made it possible for HeLa to take over so many other cultures-they simply outlived and outgrew any other cells they encountered."
-Darwin
