EACH ANTIBODY MOLECULE BEARS TWO IDENTICAL BINDING SITES CONSISTING OF SIX b-LOOPS.
DEFENSE OF HUMAN EXISTENCE :
An individual exists in the natural world by his biological abilities to defend his continued existence as an independent entity. This essay explores the physiological aspects of human existence and the defensive mechanisms that sustain this existence and the molecules which define and shape our ‘INDIVIDUALISM’. I had earlier described the Cultural aspects of ‘INDIVIDUALISM’ while describing the Indian Identity and in the ‘tag cloud’ that essay is identified as individualism. The term ‘immunity’ describes the natural defensive mechanisms that give an individual the ability to recognize foreign proteins and foreign substances and neutralize or degrade them with or without injury to the individual’s own tissues. Immunology is the branch of science concerned with the body’s response to foreign agents and substances.
FUNCTIONS OF THE IMMUNE SYSTEM :
The immune system responds to invasion by the foreign organisms and their toxic products. This immune response is also described as ‘active immunity’. In natural world, an infant is defended by molecules transferred passively across the placenta from the mother’s circulation during the fetal stage of development. The infant after birth may also receive passively protein molecules from mother when breast fed. This passive immunity defends the baby for several months and the baby further survives by developing its own immune system. Another major function of the immune system is the removal of damaged, or dying cells. The immune system is also able to recognize and eliminate abnormal or ‘mutant’ cells that frequently arise within the body. Using a system that is described as ‘immune surveillance’, the body recognizes and disposes of such abnormal cells which could result in the incidence of certain types of cancer. The immune system plays a vital role in protecting body from bacteria, viruses, fungi, and parasites and also helps to prevent certain types of cancer.
The immune system is very important and it is also very sensitive. The system’s very ability to recognize foreign substances may often result in undesirable reactions. Millions of people suffer on account of ‘hypersensitivity’ or allergic reactions to fairly harmless substances present in the environment. Many individuals suffer on account of their sensitivity to proteins found in the foods such as milk, eggs, fish, wheat(gluten), and nuts that we consume. Sometimes, the immune system is misdirected and initiates an immune response against the body’s own cells or tissues producing a condition known as an ‘autoimmune disease’. While an immune system could cause some problems, we take full advantage of the system to defend ourselves from serious infectious diseases such as smallpox,polio,rabies, diphtheria, whooping cough, measles, rubella, mumps, tetanus, typhoid, cholera, tuberculosis, hepatitis B, influenza and others by using vaccines and inoculations. Millions of lives are protected by the routine use of vaccines and inoculations which help the body to become resistant to these infectious agents. We also use foreign proteins to protect the lives of people in times of a severe life threatening crisis. We use blood, plasma, and sera( containing immunoglobulins secreted by animals) with utmost care to tide over an emergency.I had personally used foreign immunoglobulins to treat snake bite victims and tetanus cases. The foreign proteins elicit a minor immune response and the situation is carefully monitored. By being careless and reckless, and by polluting our food, water, air , and soil with dangerous chemicals, we damage our very sensitive immune system and this is contributing to a higher incidence of immune-related health problems in population.
TYPES OF IMMUNE RESPONSE :
The immune system defends human existence with a variety of different cells and by the protein molecules known as immunoglobulins or ‘antibodies’ produced by the immune function capable cells. The ability to recognize foreignness, the specificity of the response, and the memory of the prior immune response are the key characteristics of immune defense. The immune system must be able to recognize the foreign agents and foreign materials in order to locate and destroy them. Specificity means that immunity to one foreign substance or organism does not provide resistance to another type of organism. Memory is the ability of the individual to develop an accelerated, enhanced, and long-lasting immunity after the initial attack by an infectious disease. The body defends itself through two types of mechanisms which work together to protect our existence. 1. Humoral Immunity- this invloves production of protein molecules described as immunoglobulins or ‘antibodies’.2. Cell-mediated Immunity- It does not involve the secretion of ‘antibodies’ but requires direct physical contact with the foreign substance or agent.
HUMORAL IMMUNITY :
The cells known as Lymphocytes or B cells are produced in the bone marrow and circualte in our blood and are distributed to the various lymphoid tissues in the body, such as the lymphnodes, spleen, tonsils, and Peyer’s Patches that line the small intestine. When stimulated by an infectious organism, the production of lymphocytes increases and the lymphocytes are carried to the site of infection. Depending upon the site of infection, the lymphnodes of that region often swell up and are found packed with lymphocytes. The B cells produce chemical substances known as ‘antibodies’. These are protein molecules which are specifically generated against specific organisms. The foreign substance is described as ‘antigen’. The ‘antibodies’ that are generated recognize their antigens with high affinity and extreme selectivity. The interaction of an ‘antigen’ with its specific ‘antibody’ involves only small areas on the antigen’s surface; these areas are known as ‘antigenic determinants’. Protein molecules are very potent antigens as they have several antigenic determinants. Many carbohydrates are also antigenic because they have antigenic determinants. The antibodies circulate in the blood. The simplest, most prevalent means by which the immune system defends the body against bacteria and viruses is by the combination of a specific antibody with the antigenic determinants located on the surface of the invading organism. This interaction between antibodies and antigens producess an aggregate of cells called as an ‘agglutination’. The body has wandering scavenger cells known as ‘Macrophages’. The clumps of agglutinated cells are engulfed and digested by the macrophages. Antibodies also bind to toxic molecules given off by invading microorganisms and this reaction produces large, insoluble aggregates known as ‘precipitates’. These precipitates are also removed by macrophages. The virus after entering the body survives by its ability to invade or enter cells. Antibodies prevent the ability of virus to infect cells by covering up and blocking the attachment sites of virus.
CELL-MEDIATED IMMUNITY :
There are another distinct type of Lymphocytes known as T lymphocytes or T cells. T cells originate in the THYMUS and also become localized in lymphoid organs. The immunity associated with T cells does not involve the secretion of antibodies but through their direct contact with their targets or by the effects of secreted molecules known as ‘lymphokines’ which help other cells to make the direct contact. There are four kinds of T cells. 1. The cytotoxic T cells
or Natural Killer cells or NK cells defend the body by destroying infected, foreign or cancerous cells. The other three kinds of T cells regulate immune responses by secreting messenger proteins known as lymphokines. 2. Helper T cells- enable the other T cells and most B cells to perform their functions. The Helper T cells are destroyed by the Human Immunodeficiency Virus(HIV) in Acquired Immune Deficiency Syndrome(AIDS) patients resulting in a depressed immune response that allows infection by a variety of microorganisms and the growth of some types of cancerous tumors. AIDS patients are very vulnerable to fatal infections. 3. Suppressor T cells dampen the immune response of the B and T cells. 4. The fourth kind of T cell is involved in certain kinds of hypersensitivity reactions. In a normal healthy individual there is a balanced ratio of these four kinds of T cells to provide an efficient immune system for defense against all foreign substances. Macrophages and White blood cells known as ‘neutrophils’ have the ability to engulf and digest particulate matter by the process of ‘phagocytosis’. They eliminate many foreign organisms and particulate materials that enter the body. The ability of NK cells to kill or destroy some cancerous or tumor cells is enhanced by two lymphokines known as ‘gamma interferon’ and ‘interleukin-1’. Another lymphokine known as ‘interleukin-2’ activates the Lymphokine Activated Killer Cells or LAK cells which also have the ability to kill a variety of human tumor cells. Activated T cells also secrete a lymphokine known as Transfer Factor which is able to cause normal lymphocytes to release lymphokines or otherwise become activated and thus to destroy other cells. Transfer Factor stimulates the lymphocytes to develop normal immunity.
The Cytotoxic T cells destroy other cells by interacting with antigens present on the cells’ surfaces. They are involved in the attacks on tissues and organs grafted or introduced into the body, viral antigens found on infected cells and on chemicals that have entered the body and found attached to cells. T cells are involved in skin reactions resulting from contact with molecules found in poisonous plants like poison Ivy, poison Sumac, and poison Oak.
ORGAN TRANSPLANTATION AND CELL-MEDIATED IMMUNITY :
T cells are involved in the rejection of transplanted tissues and organs. The chances of successful organ transplantation are improved by carefully matching the tissue or Histocompatibility Antigens known as the HLA system of the donor with those of the recipient. The protein molecules of the HLA Complex establish the identity of our body, its tissues, and various organs. They work to preserve the identity of the individual and to exclude the introduction or grafting of foreign material into the body. Even after careful matching, and selection of suitable donors, transplanted tissues or organs are usually maintained by using drugs that cause ‘immunosuppression’ by which the normal immune response of the recipient against the donated organ is prevented.
BIOLOGICAL EXISTENCE :
A normal, healthy immune system is vital to defend our biological existence. Immunodeficiency diseases, depressed or compromised immune system conditions such as associated with corticosteroid therapy, chemotherapy, radiation therapy, or exposure to certain types of toxic chemiclas, and autoimmune diseases impose a heavy burden and threaten our existence. Medical interventions and treatment may help us but the quality of life is invariably compromised. A functioning immune system is important to defend our existence.
MOLECULAR INDIVIDUALISM :
The unique protein molecules that we deploy to establish our identity, and to defend our existence exhibit ‘individualism’ at molecular level. Molecules can exhibit a surprising degree of individuality. In experiments that examine the physical behavior of single molecules, researchers at Stanford University have discovered that when identical ‘polymers’- long, flexible, spaghetti-like molecules that are found in everything from plastics to living cells( the strands of DNA and other protein molecules)- they UNFOLD in a variety of different ways even when exposed to the same conditions. Nobel Laureate Dr. Steven Chu, former Professor of Physics, and Applied Physics at Stanford( presently United States Secretary of Energy) has stated that : “We discovered it because we have developed the ability to visualize and manipulate single molecules…. ONLY BY LOOKING AT INDIVIDUAL ANIMALS CAN YOU GET A TRUE SENSE OF THE DIVERSITY OF SPECIES.” He had researched biological Physics and Polymer Physics at single molecular level. He made use of individual molecules of DNA to study Polymer Dynamics.
The Theory of Evolution fails to account for our Molecular Individualism. Our body is unique and does not display any affinity to foreign substances and proteins and is actually involved in degrading or destroying such invasion by foreign agents and their products. The body has no evolutionary preferences and the vigorous response of the immune system has no bearing upon any presumed evolutionary connections between species. We need to look at each human individual to truly understand the nature of our Human Diversity. When we look at the genetic code, the DNA molecules that operate this code, we can understand the nature of our Molecular Individualism. Man comes into existence as an Individual and he exists an individual according to the Law of Individuality.
Dr. R. Rudra Narasimham,
Kurnool Medical College, Kurnool, A.P., India.,
M.B.B.S., Class of April, 1970.