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Lymphocytes play an important part in the healthy running of our immune systems, and there are three different types. T cells and B cells are the primary cells that are involved in the adaptive immune response system (the part of the immune system that is able to recognize and remember specific foreign invaders and help the body build up an increasingly stronger defence strategy each time it encounters a specific allergen.)  T cells target cells that have foreign antigens attached to their receptors and help to destroy them (apoptosis or programmed cell death). They also play a role in alerting other cells to release various chemicals (proteins, cytokines, amines). T cells often work best in responses against bacteria, viruses, protozoans and fungi. B cells, with proper stimulation, can transform into plasma cells which secret antibodies. These secreted antibodies will then bind to specific antigens on invading cells, which will mark them for destruction.

Both T and B cells are designed to identify ‘non self’ antigens and help to initiate responses within the body that will lead to their destruction.  Each T and B cell will leave a record of the antigens they have come in contact with in what is termed a memory cell. Memory cells last throughout the life of the body they are in and leave specific instructions to the immune system on how best to defend the body if they are ever encountered again.

Natural Killer Cells are the third type and these cells mainly help the body in its defence against tumours and viral cell infections. Once stimulated by cytokines NK cells release a substance that kills targeted cells.