The Basic Concept about Immunology

The Three level of Host defenses: 

1. The first line of defense is an inborn, non-specific system composed of anatomical, chemical, and genetic barriers that block microbes at the portal of entry. 
2. The second line of defense is also inborn and nonspecific and includes protective cells and fluids in tissues, and , 
3. The third line of defense is acquired and specific and is dependent on the function of T and B cells.

Immunity/ Immunology: 

1. Immunology is the study of immunity, which in turn refers to the development of resistance to infections agents by the body. Immunity is marked by white blood cells (WBCs), which conduct surveillance of the body, recognizing and differentiating self and non-self (foreign) cells by virtue of the markers they carry on their surface. Under normal conditions self cells are left alone, but non-self cells are destroyed. 
2. For purpose of immunologic study, the body is divided into three compartments: The blood, lymphatic, reticuloendothelial system. A fourth component, the extracellular fluid, surrounds the first Three and allows constant communication between all areas of the body.

Circulatory system:  Blood and Lymphatics

1. Whole blood consists of blood cells (formed by hemopoiesis in the bone marrow) dispersed in plasma, stem cells in the bone marrow differentiate to produce white blood cells (leukocytes), red blood cells (erythrocytes), and megaryocytes, which give rise to platelets. 
2. Leukocytes are the primary mediator of immune function and can be divided into granulocytes (neutrophil, eosinophil, basophils) and agranulocytes (monocytes, and lymphocytes) based on their appearance. Monocytes later differenciate to become macrophages. Lymphocytes are divided into B cells and T cells, which participate in cell-mediated immunity,  and Leukocytes display both chemotaxis and diapedesis in response to chemical mediators of the immune system. 

Lymphatic system: 

1. The lymphatic system parallels the circulatory system and transports lymph while also playing host to cells of the immune system. Lymphoid organs and tissues include lymph nodes, the spleen, thymus, as well as areas of less well organized immune tissues such as GALT, SALT, MALT, and BALT. 

Generalized immune response: 

1. The inflammatory response is a complex reaction to tissue injury marked by Redness, heat, swelling, and pain. 

• Blood vessels narrow and then dilate in response to chemical mediators and cytokines
• Edema swells tissues, helping prevent the spread of infection
• WBCs, microbes, debris, and fluid collect to form pus
• Pyrogens may induce fever.
• Macrophages and neutrophils engage in phagocytosis, engulfing microbes in a phagosomes. Uniting the phagosome with a lysosome resulf in destruction of the phagosome contents. 

Chemical defenses

1. Interferon (IFN) is a family of proteins produced by leukocytes and fibroblasts that inhibit the reproduction of viruses by degrading viral RNA or blocking the synthesis of viral protein. 
2. Complement is a complex defense system that results, by way of a cascade mechanism, in the formation of a membrane attack complex that kills cells by creating holes in their membranes

Characteristics of Acquired immunities:

1. Immunocompetent individuals posses a third line of defense that is acquired only after exposure to an infectious agent. This type of immunity is mediated by T and B lymphocytes and is marked by being extremely specific and creating immunologic memory.