TOPIC 1.CLASSIFICATION KINGDOM FUNGI

White blood cells are produced in the bone marrow and in the lymph nodes.

The function of white blood cells is to protect body against infection. They perform this function by:

                            

                             Phagocytosis in a white blood cell

1. Engulfing and destroying pathogens (a process called phagocytosis).                                                                                                     
2. Producing substances that neutralize toxins produced by pathogens.
3. Causing   clumping   together   of   foreign materials in the body.
4. Killing infected body cells.
5. Preventing clotting in damaged tissues.

The effect of HIV on white blood cells

The Human Immunodeficiency Virus (HIV) attacks a type of white blood cells called helper-T cells. These cells are essential for body immunity. When they encounter an antigen, the helper-T cells divide themselves to form new cells. This increases the number of cells available to fight the infection. After the infection, some cells remain as memory cells to activate an immune response if the infection happens again, in addition helper-T cells activate other cells in the immune system.

HIV has a protein envelope that can only bind to its receptor called CD4 found on the cell membrane of the helper-T cell. When it enters the human body, HIV fuses its protein envelope with the CD4 then enters the cell. Once inside the cell, the virus becomes part of the helper-T cell and replicates together with it as it undergoes division. This increases the amount of HIV in the blood. The HIV destroys helper-T cells resulting in the reduction of the number of helper-T cells and reducing the CD4 count.