White blood cells Lecture by Dr Sandeep :30 – 10:30 am

Leukocytes (white blood cells) are the mobile unit of the body They are formed partially in the bone marrow and partially in the lymph tissue

Genesis of WBCs

General characteristics of leukocytes There are 6 different types of WBCs Polymorphonuclear neutrophils (62%) Polymorphonuclear eosinophils (2.3%) Granulocytes Polymorphonuclear basophils (0.4%) Monocytes (5.3%) Agranulocytes Lymphocytes (30%)

Neutrophils

Neutrophils and macrophages Mainly neutrophils and tissue macrophages that attack and destroy invading bacteria, viruses, and other injurious agents Steps of Phogocytosis 1) WBCs attaches to vascular wall called margination 2) WBCs enter tissue spaces by diapedesis 3) Move through the tissue by ameboid motion 4) Attracted to the inflammed tissue by chemotaxis –The agents could be, bacterial and viral toxins, degenerative products of inflamed tissue, reaction products of complement complex, reaction products of blood clotting 5) Last step is phagocytosis proper

Phagocytosis proper Means cellular ingestion, this depends mainly on 1)Texture of the materials to be phagocytes 2) protective protein coats 3) Opsonization Once phagocytosed most particles are digested by intracellular digestive enzymes

The digestion takes place by emptying granular content into formed vacuoles. The granules contains various proteases plus antimicrobial agents called Defensins. In addition to this cell-membrane bound enzyme NADPH oxidase is activated with the production of toxic oxygen metabolites. NADPH + H + + 2O 2 NADP + + 2H + + 2O -

Activation of NADPH oxidase is associated with a sharp increase in O 2 uptake and metabolism in the neutrophils, this phenomenon is called as “respiratory burst” O 2 - is a free radical formed by the addition of one electron to O 2. SOD-1 O O H + + H + H 2 O 2 + O 2 O 2 - and H 2 O 2 both are oxidants that are effective bactericidal agents.

Monocytes

Macrophage in action

Monocyte-macrophage cell system Tissue macrophage in the skin and subcutaneous tissue (histiocytes) Macrophages in the lymph nodes Alveolar macrophages in the lungs Macrophages (Kupffer cells) in the liver sinusoids

Eosinophils

The eosinophils normally constitute about 2% of all the blood cells They are weak phagocytes, and they exhibit chemotaxis They are often produced in large number in people with parasitic infections, and they migrate in large number into tissue diseased by parasites

Although, most parasites are too large to be phagocytized by eosinophils, they attach them selves to the parasites by the way of special surface molecules and release substances that they can kill They do this in several ways 1)By releasing hydrolytic enzymes from their granules, they are modified lysosomes 2) By releasing highly reactive form of oxygen which is lethal to the parasites 3)They also release larvacidal polypeptide called major basic proteins

Basophils

The basophils in the circulating blood are similar to the large tissue mast cells located outside the capillaries They release histamine, as well as smaller quantities of bradykinin and serotonins They play important role in some type of allergic reactions

The allergy producing antibody like IgE type has a special propensity to become attached to these cells When specific antigen reacts with these antibodies results in release of large quantity of histamine, bradykinin, serotonin, heparin, number of lysosomal enzymes These substances cause local vascular and tissue reactions that cause most of allergic manifestation

The leukemias Uncontrolled production of white blood cells can be caused by cancerous mutation of a myelogenous or lymphogenous cell, called leukemia. These are divided into two general types: lymphocytic leukemias and myelogenous leukemias.

A clinical condition known as leukopenia occasionally occurs in which the bone marrow produces very few WBCs. Causes: Irradiation of the body by X-rays or gamma rays, or exposure to drugs and chemicals that contain benzene or antracin neuclei. Some of the common drugs such as chloramphenicol (an antibiotic), thiouracil (used in thyrotoxicosis)