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Biology lesson 5:

 – Dr Sayan Bhattacharyya 
  WBCs play abcery important role in innate and adaptive immunity. WBCs can be granulocytes and agranulocytes.
  Granulocytes have granules in cytoplasm. They are if 3 types: Neutrophils, Basophils and Eosinophils. Out of these Neutrophils are most common. They are commonly found in pus which occurs after acute infection, and so are also called Pus cells.
Neutrophils have lobed nuclei and perform immune protection in acute inflammation or infection, especiallybacterial infections. They engulf the microbes and foreign substances by phagocytosis and destroy it within their lysosomes. These lysosomes contain enzymes like Myeloperoxidase that kill the engulfed microbes. 
 Eosinophils are important in allergic responses, anaphylaxis and Type I hypersensitivity reactions. Basophils are also important in hypersensitivity. 
 Agranulocytes are of 2 types: Macrophages and Lymphocytes. Both are important for chronic inflammation or chronic infections. 
 When the infection becomes chronic, the macrophages fuse together into Giant cells. Thereafter the macrophages, giant cells and lymphocytes together form something called granuloma to surround and restrict the foreign particle. This is very commonly seen in Tuberculosis. Macrophages ae large cells and have kidney shaped nuclei. 
 Lymphocytes have large round nucleus. They are also important for adaptive or acquired immunity and can be T lymphocytes or B lymphocytes. 
 All WBCs are produced in red bone marrow. However the T lymphocytes mature in Thymus and B lymphocytes mature in Red bone marrow only. The name B lymphocyte is after *Bursa of Fabricius* which is their organ of maturation in birds.
T lymphocytes either destroy the foreign particles or suppress the immune response. They can also help the B lymphocytes in producing immunoglobulins or antibodies. 
In next class we shall study about the immune system in more details.

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