IMMUNOLOGY

IMMUNOLOGY                                                                                                                                                   is a broad branch of biomedical science that covers the study of all aspects of the immune system in all organisms. It deals with the physiological functioning of the immune system in states of both health and disease; malfunctions of the immune system in immunological disorders (autoimmune diseases, hypersensitivities, immune deficiency, transplant rejection)                                      IMMUNITY: is a biological term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion. In other words, it is nothing but the capability of the body to resist harmful microbes from entering the body.                                                                                           IMMUNE RESPONSEThe immune response is how your body recognizes and defends itself against bacteria, viruses, and substances that appear foreign and harmful.OR The immune response may be defined as the development of specific altered reactivity following exposure to an antigen.                                                   IMMUNE RESPONSE TAKES SEVERAL FORMS:                                                                                       Humoral immune response.                                                                                                                       Cell mediated immune response.                                                                                         Immunological tolerance.                                                                                                                       HUMORAL IMMUNE RESPONSE:   The term "humoral" refers to the non-cellular components of the blood, such as plasma and lymphatic fluid. The humoral immune response denotes immunologic responses that are mediated by antibodies. However, both B and T lymphocytes are necessary for the formation of antigen-specific antibody.                                                                             1.Humoral immunity includes the primary and secondary immune responses to antigen.                                                                                                                                       2.During the primary immune response, an antigen is encountered by the host for the first time. Virgin B cells need to be activated and proliferate before an effective immune response can be generated.                                                                            3.The primary response may be too slow to protect against many pathogens, therefore polyspecific natural antibodies with low affinity and the innate immune system may be utilized to limit microbial replication at the onset of infection.                                                                                                                                             4.The secondary antibody response, which results from the activation of a memory B cell, is faster and more effective in halting the progress of infection due to increased antibody binding affinities.                                                                                    CELL-MEDIATED IMMUNE RESPONSE:  Is an immune response that does not involve antibodies but rather involves the activation of phagocytes, natural (NK), T-lymphocytes, and the release of various cytokines in response to an antigen.                                                                                                                                                               Cell-mediated immunity is directed primarily at microbes that survive in phagocytes and microbes that infect non-phagocytic cells. It is most effective in removing virus-infected cells, but also participates in defending against fungi, protozoans, cancers, and intracellular bacteria. It also plays a major role in transplant rejection.                                                                                           IMMUNOLOGICAL TOLERANCE:  A time will come that immune response stops against the antigen which is continuously introducing in the body because it become habitual and tolerant to it so no immune response develops against it. TYPES OF IMMUNITY:                                                                                                                                                  There are two types of immunity:                                                                                                           1.Non-specific OR Innate immunity                                                                                                2.Specific OR Acquired immunity OR Adaptive immunity.

NON-SPECIFIC OR INNATE IMMUNITY:                                                                                     Natural immunity, native or nonspecific, immunity is the natural resistance with which a person is born. It provides resistance through several physical, chemical, and cellular approaches. Microbes first encounter the epithelial layers, physical barriers that line our skin and mucous membranes.                                                                                                               The phagocytes express cell surface receptors that can bind and respond to common molecular patterns expressed on the surface of invading microbes. Through these approaches, innate immunity can prevent the colonization, entry, and spread of microbes.                                                                                                             FIRST LINE OF DEFENCE – NON-SPECIFIC BARRIERS                                                                                             These are a combination of physical and chemical barriers that prevent all types of foreign agents from penetrating the outer layer of the body. No specific foreign agent is targeted at this level.                                                                                                                                                            The barriers are:

Ø The skin – provides an impervious barrier to pathogens.

Ø Mucous membranes – line the entrances to the body such as in the respiratory tract entrances. Mucus produced by these membranes traps foreign particles and directs them out of the body.

Ø Hairs and cilia – (nasal hairs) trap dust and dirt; (microscopic cilia) line some mucous membranes and direct foreign particles out of the body.

Ø Gastric juice, vaginal secretions and urine – acidic fluids that have a protective function.

Ø Tears, sweat and saliva – body fluids which possess some anti-bacterial properties.

Ø Cerumen (ear wax) – produced in the ear canal and protects the canal by trapping dirt and dust particles.

SPECIFIC, AQUIRED OR ADAPTIVE IMMUNITY:   Is often sub-divided into two major types depending on how the immunity was introduced.Naturally acquired immunity occurs through contact with a disease causing agent, when the contact was not intentional.                                                                              Artificially acquired immunity develops only through deliberate actions such as vaccination. Both naturally and artificially acquired immunity can be further subdivided depending on whether immunity is induced in the host or passively transferred from an immune host.                                                                  ACTIVE IMMUNITY: Is induced in the host itself by antigen, and lasts much longer, sometimes lifelong. Active immunity is generally long-term and can be acquired by infection followed by B cells and T cells activation, or artificially acquired by vaccines, in a process called immunization. Thus, an active immunity often involves humoral immunity (B-cells) and cell-mediated immunity (T-cells).

TYPES OF ACTIVE IMMUNITY:

1.     Naturally acquired active immunity

2.     Artificially acquired active immunity                                                                      Naturally acquired active immunity:  Occurs when the person is exposed to a live pathogen, develops the disease, and becomes immune as a result of the primary immune response. Artificially acquired active immunity:  Can be induced by a vaccine, a substance that contains the antigen. A vaccine stimulates a primary response against the antigen without causing symptoms of the disease.                                            PASSIVE IMMUNITY: Is acquired through transfer of antibodies or activated T-cells from an immune host, and is short lived—usually lasting only a few months.                                                                                               TYPES OF PASSIVE IMMUNITY:

1.     Naturally acquired passive immunity

2.     Artificially acquired passive immunity                                                           Artificially acquired passive immunity: is a short-term immunization by the injection of antibodies, such as gamma globulin, that are not produced by the recipient's cells.                                                                            Naturally acquired passive immunity: occurs during pregnancy, in which certain antibodies are passed from the maternal into the fetal bloodstream. Immunologic tolerance for foreign antigens can be induced experimentally by creating conditions of high-zone tolerance, i.e., by injecting large amounts of a foreign antigen into the host organism, or low-zone tolerance, i.e., injecting small amounts of foreign antigen over long periods of time                                                                            THREE LINES OF DEFENSE AGAINST PATHOGENS                                  The human body’s first and second line of defenses act against potentially infectious and harmful agents like microorganisms, chemicals and toxins. As for nonspecific defenses, there are two ways in which the body puts up a fight to stop pathogens from entering the body: external barriers, and internal defenses.

THE FIRST LINE OF DEFENSE: The body’s first line of defense against pathogens is to not let them into the body. To stop the pathogens from entering the body, we have our skin, tears, sweat, and saliva. Lysozyme within the tears and saliva, for example, can actually break down some foreign agents to make them harmless.                                                                                               THE SECOND LINE OF DEFENSE:  If some do make it inside the body, another non specific response is with white blood cells, such as macrophages, and neutrophils. In this second line of defense, these cells target anything that they recognize as not belonging to the body. They do not need antibodies to recognize the invaders, but after recognizing a certain pathogen, they will stimulate other lymphocytes to respond. The body also produces defensive proteins, known as interferon’s (to protect against viral infection), and complement proteins which cause an invading cell to lyse (burst out).                           THE THIRD LINE OF DEFENSE:  In the third line of defense, antibodies which are soluble proteins, bind to unwanted cells marking them for destruction (as with a virus, for example). In addition, many copies of the antibody for this virus will be made so the virus can be recognized the next time it enters the body. At this level, there are two types of immunity: humoral and cell mediated defenses. In humoral immunity (antibody mediated immunity by B cells and lymphocytes), antigens circulate the body looking for foreign cells, which they mark for destruction by cell eaters such as macrophages or neutrophils. These special binding proteins are produced by B cells.   In cell mediated immunity, T-cells (T-helper and T cytotoxic) work together to kill unwanted cells                                                                                           Cell mediated immunity involves the release of certain kids of cytokines. In effect, the cells are releasing substances to kill invading cells, or simply marking them for destruction by macrophages.