1. Specificity: specific activity for each type of pathogens. Immunity is directed against a particular pathogen or foreign substance.

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1 L13: Acquired or adaptive (specific) immunity The resistance, which absent at the time of first exposure to a pathogen, but develops after being exposed to the pathogen is called acquired immunity. It includes specific cells of the immune system that ate able recognize and response to the foreign materials. The cells involved in this type of immunity are lymphocytes both T and B cells. Properties of acquired or adaptive (specific) immunity Also known as acquired immunity, resist a particular foreign agents, moreover, specific immune response improve on repeated exposure to the same agents, many characteristic distinguish specific immunity from non- specific immunity: 1. Specificity: specific activity for each type of pathogens. Immunity is directed against a particular pathogen or foreign substance. 2. Memory: when exposed to the same pathogen or substance the body reacts so quickly that there is no notice able pathogenesis, Recognition to the specific sites on the foreign substances (Ag) needs at first a certain time so innate immunity is faster than specific immunity but the later is more effective and the program of the solid immunity against infectious disease depend on the activation of specific immunity. Response results in immunologic memory very important characteristic feature that the concept of vaccination depends on 3. Diversity: the system is able to generate an enormous diversity of molecules such as antibodies that recognize billions of different antigens. 4. Discrimination between self and non self. The specific immune system always responds only to non self antigens thus, does not attack human itself. 5. Response is antigen dependent. 6. The effectiveness toward antigens increases following subsequent exposure to the same antigens. Thus second contact with the same antigens increases the immune response through antibodies or sensitized memory cells. Classification of acquired or adaptive (specific) immunity According to the nature of components of immune mediated reactions: A:Humoral immunity(hi): mediated by specific glycoproteins (immunoglobulins or Ab). 1

2 B: Cell mediated immunity (CMI): mediated by specific cells which are T lymphocytes. Also, specific immunity can be classified according to the rout of acquirement into: 1. Natural immunity A: passive (placental transfer of Ab). B: Active (as response to the infection). 2. Artificial immunity A: passive (administration of Ab e.g. antitoxin antibodies). B: Active (vaccination: administration of attenuated live or killed foreign invaders to stimulate the immune system). 1-Humoral (antibody mediated) immunity It is antibody (Abs.) dependent and relies upon body fluids especially the lymph and blood plasma to spread Abs. around the body. The Abs. is produced by B- lymphocyte and it is thought that processing of B-cell occurs in bone marrow and fetal liver. There are five classes of Abs. each are called immunoglobulin as fallow: 1-IgA (15% of total Abs. count) found in mucous secretion of respiratory and digestive tract, vagina and in colostrums the substance is produced before the milk after delivery will protect the baby for about six months. 2-IgD (less than 1%) appears to have a role in activating and suppressing lymphocyte activity. 3-IgE (less than 1%) it is mediator in allergic response, activate histamine secreting cells and play role in parasitic infection. 4-IgG (75% of total count) stimulate phagocyte cells, activate the complement system and neutralized toxins. It is the only Abs. that can cross the placenta and confer immunity on the fetus. 5-IgM (10% of total Abs.) this is the predominant early Abs. that activate in an initial attack of Ag. Because of it is high number of antigen binding sites have 5 sites (Fig.),this is important in an initial activation of B cells macrophage and complement system. 2

3 Fig. sites of binding antibodies with antigens 2-Cell mediated immunity It is involved T- lymphocyte cell, that is originally derive from stem cells of the bone marrow and then passes to the thymus gland in the chest, where they multiply. Cell mediated is based on the action of specific kinds of cell T- lymphocyte that directly attack cells infected with viruses or parasites, transplanted cells or organs and cancer cells.tlymphocyte can lyses these cells or release chemicals like cytokines that enhance specific immunity and non- specific defenses such as phagocytes and inflammation. The cells responsible for specific and non- specific immunity are leukocytes (meaning white cell) from the stem cells which migrate to the other body sites undergo further development, some become residents within tissues while others circulate in body fluids. In figure below there are different types of leukocyte: 1-Lymphoid cells Lymphocyte are major cells of specific immune system, lymphocyte can be divided into three populations T, B and natural killer (NK) cells. 2- Mononuclear cells There are two types of mononuclear: monocyte & macrophages are highly phagocytic were engulfed & destroyed pathogenic M.O. 3- Granulocytes 3

4 Have irregular- shaped nuclei with 2-5 lobes and the cytoplasm matrix has granules contain reactive substances which kill M.O. There are three types of granules: neutrophil, acidophile, basophile. LEUKOCYTES: White Blood Cells Granular leukocytes (granules in cytoplasm) Nongranular leukocytes (do not have granules in their cytoplasm) non Fig. Leukocytes types divisions Lymphoid cells mononuclear cells 4

5 Neutrophile Acidophile Basophile 5