2nd Year Medicine- IBLS Module May 2008 IBLS Lecture 11 White Blood Cells (Leucocytes)

2nd Year Medicine- IBLS Module May 2008 Objectives At the end of the lecture you should be able to: 1.Describe the role of WBCs in the body defence mechanisms. 2.Describe the normal functions of the various WBCs. 3.Describe the role of diapedesis, chemotaxis, phagocytosis as function of the WBCs. 4.Describe the basic concept of innate and acquired immunity. 5.Describe the functional classification of lymphocytes. 6.Describe the cells participating in cellular & humoral immunity.

2nd Year Medicine- IBLS Module May 2008 White blood cells WBC: mobile units of the body's protective system. Normal count is ,000 /µL Types: Granulocytes (Polymorphnuclear or "polys"): –Neutrophils 60 % –Eosinophils 2 % –Basophils 0.4 % Agranulocytes (mononuclear): –Lymphocytes 30 % –Monocytes 5 %

2nd Year Medicine- IBLS Module May 2008

Life span Granulocytes: 4-8 hours in blood, 4-5 days in tissues. Monocytes: hours in blood, months in tissue (tissue macrophages) Lymphocytes live for weeks or months.

2nd Year Medicine- IBLS Module May 2008 Neutrophils and Macrophages defend against infections

2nd Year Medicine- IBLS Module May 2008

Phagocytosis Definition: Cellular ingestion of the offending agent. Most important function of neutrophils and macrophages. Selective process. Phagocytosis is increased if: –Surface of particle is rough. –Lacks protective protein coat. –Binding of antibodies to antigen (opsonization).

2nd Year Medicine- IBLS Module May 2008 Phagoytosis by neutrophils Also called polys: first line of defense in bacterial infections. Mature cells that can attack and destroy bacteria even in the circulating blood. Attach to the particle and project pseudopodia around it→ an enclosed chamber that contains the phagocytized particle which breaks away → free floating phagosome. Can phagocytize 3-20 bacteria before it dies.

2nd Year Medicine- IBLS Module May 2008

Phagocytosis by monocytes Immature in blood (1-2 days) In tissues → mature and enlarge → tissue macrophages. Much more powerful phagocytes than neutophils. Can phagocytize as many as 100 bacteria. Can engulf large particles e.g. malarial parasites. Can survive after phagocytosis for months.

2nd Year Medicine- IBLS Module May 2008

Neutrophils and monocytes reach the site of infection by the following mechanisms: They squeeze through the pores of the capillaries by diapedesis. They move toward the site of infection by amoeboid movement. Different chemicals released by microbes and inflamed tissues attract neutrophils and macrophages→ chemotaxis.

2nd Year Medicine- IBLS Module May 2008

Basophils Similar to mast cells outside capillaries in connective tissue. Both basophils and mast cells release heparin into blood, which prevent blood coagulation. Play a role in allergic reactions. When ruptured histamine and other substances released cause local vascular and tissue reactions that are characteristic of allergic manifestations.

2nd Year Medicine- IBLS Module May 2008 Eosinophils Produced in large numbers in persons with parasitic infections. They attach themselves to the surface of the parasite and release substances that kill the invading parasite. Release of eosinophil chemotactic factor from mast cells and basophils → make them collect in tissues in which allergic reaction has occurred → prevent the spread of the inflammatory process (detoxify substances and destroy Ag-Ab complexes).

2nd Year Medicine- IBLS Module May 2008 Immunity Definition: The ability of the body to resist all types of organisms or toxins that damage the tissues. Types: –Natural (innate): general protective mechanisms e.g. phagocytosis, acidic secretion and digestive enzymes of the GIT, resistance of the skin to invasion, etc... –Acquired: the ability to develop powerful protective mechanisms against specific invading agents e.g. lethal bacteria and viruses.

2nd Year Medicine- IBLS Module May 2008 Types of Acquired Immunity Humoral or B-cell immunity: involves the development of circulating Ab that are capable of attacking an invading agent. Cell mediated or T-cell immunity: is achieved through the formation of large numbers of activated lymphocytes that are specifically designed to destroy the foreign agent.

2nd Year Medicine- IBLS Module May 2008 Lymphocytes Lymphocytes are responsible for acquired immunity. They are present in lymph nodes and other lymphoid tissues throughout the body. B lymphocytes: Processed in bone marrow. When exposed to an Ag, they differentiate to plasma cells that produce antibodies (gamma globulins). This initiates the destruction of the antigen. T lymphocytes: Processed in thymus. They release chemicals that destroy target cells with which they make contact such as virus infected cells and cancer cells.

2nd Year Medicine- IBLS Module May 2008

Summary What are the different types of WBCs? What is their count and percentage? What is their role in protecting the body against infections? What are the different types of immunity? What role do lymphocytes play in acquired immunity?