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Immune system

The immune system is remarkably adaptive defense system that has evolved in vertebrates to protect them from invading pathogenic microorganism and cancer. It is able to generate an enormous variety of cells and molecules capable of specifically recognizing and eliminating an apparently limitless variety of foreign invaders. These cells and molecules act together in an exclusively adapted dynamic network whose complexity rivals that of the nervous system.

Functionally an immune response can be divided into two related activities � recognition and response. Immune recognition is remarkable for its specificity. The immune system is able to recognize subtle chemical differences that distinguish one foreign pathogen from another. Furthermore, the system is able to discriminate between foreign molecules and the body�s own cells and proteins. Once a foreign organism has been recognized, the immune system enlists the participation of variety of cells and molecules to mount an appropriate response, called an effector response, to eliminate or neutralize the organism. In this way the system is able to convert the initial recognition event into different effector responses, each uniquely suited for eliminating a particular type of pathogen. Later exposure to same foreign organism induces a memory response, characterized by a more rapid and heightened immune reaction that serves to eliminate the pathogen and prevent disease.

Immune system has both components- Non specific components and specific components.

Non specific (Innate) Immunity:

Innate immunity provides the first line of during the critical period just after the host�s exposure to a pathogen. In general, most of the microorganisms encountered by a healthy individual are readily cleared within a few days by non specific defense mechanisms before they activate the adaptive immune system.

Type	Mechanism
Anatomic Barriers Skin Mucous Membranes	� Mechanical barrier retards entry of microbes. Acidic environment (pH 3-5) retards growth of microbes. Normal flora compete with microbes for attachment ites and nutrients. Mucus entraps foreign microorganisms. Cilia propel microorganisms out of body.
Physiologic Barriers Temperature � Low pH Chemical mediators	� Normal body temperature inhibits growth of some pathogens. Fever response inhibits growth of some pathogens. Acidity of stomach contents kills most ingested microorganisms. Lysozyme cleaves bacterial cell wall. Interferon induces antiviral state in uninfected cells. Complement lyses microorganisms or facilitates phagocytosis.
Phagocytic/Endocytic barriers	Various cells internalize (endocytose) and brak down foreign molecules. Specialized cells (blood monocytes, neutrophils, tossue macrophages) internalize (phagocytose), kill,� and digest whole microorganisms.
Inflammatory barriers	Tissue damage and infection induce leakage of vascular fluid, containing serum proteins with antibacterial activity, and influx of phagocytic cells into the affected area.

Specific (Adaptive) Immunity:

Adaptive or Specific immunity is capable of recognizing and selectively eliminating specific foreign microorganisms and molecules (i.e. foreign antigens). Unlike innate immune responses, adaptive immune responses are reactions to specific antigenic challenges and display four characteristic attributes:

Antigenic specificity

Diversity

Immunologic memory

Self/Non self recognition

An effective immune response involves two major groups of cells: Lymphocytes and Antigen presenting cells. Lymphocytes are of many types of white blood cells produces in the bone marrow by the process of hematopoiesis. Lymphocytes leave the bone marrow, circulate in the blood and lymphatic systems, and reside in various lymphoid organs.