Monday, 5 November 2012

Null cells

  • Null cells are lymphocytes with cytotoxic properties.
  • They are neither B-cells not T cell. They are intermediate between T and B cells.
  • They form less than 3%.
  • There are two types of Null cells namely, Natural Killer Cells (NK cells) and Killer Cells.

Natural Killer Cells:

  • NK cells are a group of null cells.
  • They form the third population of lymphocytes.
  • The NK cells have 2 or 3 large granules in the cytoplasm. Hence they are also Large Granular Lymphocytes (LGL).
  • They have a kidney shaped nucleus.
  • The NK cells kill the target cells without the aid of antibody or complement. So they are antibody independent.
  • They destroy the cancer cells and cells infected with herpes and mumps virus.
  • They are activated by Interferons and Interleukins-2.

Killer Cells (K cells):

  • Killer cells are antibody dependent.
  • These cells possess Fc receptors for binding with IgG antibodies. Hence they can bind with cells coated with IgG antibodies and can kill them.
  • These cells can combine with specific antibody with it is in complex with antigen. If the complex is on the surface of a target cell, these lymphocytes become activated destroying the target cell.
  • This cell can kill a variety of cells such as tumor cells, bacteria, viruses, fungi and parasites.

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