Lec. 5 Nov.2015

Immune system

Immunity: is defined as the ability of human body to resist against harmful chemicals such as toxins that released by microorganism which tend to damage the tissues & organs. Lymphocytes are key constituents of the immune system. The lymphatic system includes lymphocytes, lymph nodes, tonsils, spleen, thymus gland, lymph and lymphatic vessels. There are two types of immune defense systems:

1. Innate immunity. 2. Acquired (adaptive) immunity. A-Innate immunity: in this type of immunity the body is born with the ability to recognize and destroy certain substances but cannot distinguish among different kinds of bacteria and remember previous encounters. Its components are: 1.Mechanical mechanisms: a. skin b. mucous membranes 2. Chemical mediators. 3.Cells.

4.Inflammation. when the tissue injury occurs either by bacteria or chemical there is a release of chemical mediators (also called chemotaxins or chemotactic factor ) from infected area which attract leukocytes especially neutrophils to the infected area.. The process of attraction is called chemotaix. The chemotaxins produce several effects: 1. Vasodilatation. 2. Increased vascular permeability resulting in edema 3. “walling off’’ the infected area.

There are two types of inflammation: a. localized b. systemic. Signs and symptoms of inflammation are: heat, redness, pain, swelling, loss of function and release of chemicals called pyrogens from leukocytes which cause fever and inhibit growth of microorganism. Pus formation: is dead neutrophil, necrotic tissue, dead macrophages tissue fluid. A localized collection of pus is called abscess. B- Acquired or adaptive immunity: substances that activate adaptive immunity are called antigens which are large molecules with a molecular weight of 10000 or more for example penicillin.

There are two types of antigens: a. foreign antigens: Pollen, food, drugs and dried skin. Transplanted organs and tissues that contain foreign antigens result in the rejection of the transplant. b.Self-antigens: that produced by the body itself. There are two types of acquired immunity: 1. Humoral immunity. 2. Cellular immunity. Humoral immunity: is mediated by B-lymphocytes which are produce plasma cells.Plasma cell produce circulating antibodies or immunoglobulins (Ig,s).

Humoral immunity can also cause immediate hypersensitivity reactions such as bronchial asthma. Cellular Immunity: is mediated by T-lymphocytes. It is responsible for delayed allergic reactions (such as eczema) and rejection of transplants of foreign tissue. The cytotoxic T cells destroy cells that have the antigen which activated them. One mechanism by which they kill is insertion of pore-forming molecules (perforins) in the membranes of their target cells which leads to destruction of the cells by osmotic lyses.

Immune system problems of clinical significance: Hypersensitivity (allergy): is an undesirable side effect of immunity. It is defined as an inappropriate activation of the body’s immune system which may result in a very strong inflammation and tissue damage. Types: 1.Immediate hypersensitivity: which is caused by B-cell immunity. There is reaction between antibodies and antigens. The symptoms appears within a few minutes of exposure to foreign antigen. For example, bronchial asthma, food allergies, hay fever. 2.Delayed hypersensitivity: mediated by T-lymphocytes and symptoms take several hours or days to develop. Examples, poison oak, eczema, soaps, measles, cosmetics, & drugs. Q: write short notes on the allergies in the allergic person. Give examples.