Defense Mechanisms of the Body Lecture 3.pptx

Pharm D

1. Defense Mechanisms of the Body Dr. Najam-us-Sahar Senior Lecturer

2. RESISTANCE OF THE BODY TO INFECTIONS What is Immunity? “The human body has the ability to resist almost all types of organisms or toxins that tend to damage the tissues and organs. This capability is called Immunity.” There are Two types of immunity: Innate Immunity. Acquired Immunity. Much of immunity is acquired immunity that does not develop until after the body is first attacked by a bacterium, virus, or toxin often requiring weeks or months to develop the immunity. An additional portion of immunity(Innate) results from general processes, rather than from processes directed at specific disease organism.

3. Innate Immunity Phagocytosis of bacteria & other invaders by WBC’s & the cells of the tissue macrophage system. Destruction of swallowed organisms by acid secretion of stomach & the digestive enzyme. Resistance of the skin to invasion by organisms. Presence of certain chemical compounds in blood such as; lysozyme, basic polypeptides, complement complex, natural killer lymphocytes can destroy toxins.

4. Acquired Immunity: Powerful specific immunity against individual invading agents. Forms antibodies/ activated lymphocytes that attack & destroy the specific invading organism or toxin. Immunization.

5. Types of acquired immunity There are two types : Humoral Immunity(B-cell immunity). Cell mediated Immunity(T-cell immunity). Humoral Immunity: “Body develops circulating antibodies, which are globulin molecule in the blood plasma that are capable of attacking the invading agent.” And it’s called as B-cell immunity because B lymphocytes produce the antibodies.

6. Cell-mediated Immunity: “ It is achieved through the formation of large numbers of activated T Lymphocytes that are specifically crafted in the lymph nodes to destroy the foreign agent.” And this is called as T-cell immunity because the activated lymphocytes are T lymphocytes.

7. Antigens Acquired immunity does not develop until invasion of a foreign organism or toxin occurs, so the body must have some mechanism for recognizing invasion. Each toxin always contains one or more specific chemical compounds in it’s makeup that are different from all other compounds. In general, these are large proteins or large polysaccharides, & these initiate acquired immunity. These substances are called Antigens.

8. Antigens For a substance to be antigenic, it usually must have a high molecular weight, 8000 or greater. The process of antigenicity depends on regularly recurring molecular groups, called epitopes present on the surface of large molecule. That is why proteins are always antigenic because both of these have this stereochemical characteristics.

9. Role of lymphocytes Acquired immunity is the product of body’s lymphocytes. So the person who have a genetic lack of lymphocytes or whose lymphocyte are destroyed by chemicals or radiations, no acquired immunity can be develop. Such person can die within days after birth. Lymphocytes are located most extensively in the lymph nodes, but also found in special lymphoid tissue such as spleen, submucosal areas of GIT, thymus and bone marrow.

10. Role of lymphocytes The lymphoid tissues are distributed advantageously in body to intercept invading organisms or toxins before they can spread too widely. In most instances, the invading agent first enters the tissue fluid & then is carried by lymph vessels to lymph nodes or other lymphoid tissues. EXP: The lymphoid tissue of GIT walls is exposed immediately to antigens invading from gut.

11. Immunoglobulins ( Ig ) Each antibody is specific for a particular antigen. This is caused by it’s unique structural organization of amino acids in variable portion of the light & heavy chains. There are 5 general classes of antibodies: IgM, IgG, IgA, IgD & IgE. Two of these classes are of particular importance; IgG & IgE.

12. Immunoglobulins ( Ig ) IgG It is a bivalent antibody & constitute about 75% of antibodies of normal person. IgE which constitute only a small percentage of antibody but is involved in allergy. IgM class is also important, because antibodies produce during primary response are usually of this type. IgA involves body secretions. IgD recognize antigens by B cells.