Immunity can be divided into innate immunity and acquired immunity. The mechanisms of innate immunity are given to us by our Creator as a tool with which to protect ourselves. These are used to fight against every kind of microorganism. These ever-ready forces do not need to have met the enemy microorganisms to fight them off. Acquired immunity comes about after the infectious microbe has been encountered; this is usually as a result of infection or vaccination. Such immunities only protect the body against a specific harmful organism. T and B lymphocytes and antibodies belong in the acquired immune system, whereas other mechanisms are part of the innate immune system. We can classify the very intricate immunity mechanisms as follows:

A – Layers that cover the inner and outer surfaces of the body: These are the physical structures that carry out the task of protection by covering the tissues like a shield or fortress.

1. Skin: Our skin is an organ in its own right. It is created with such perfect characteristics that no microorganism can penetrate our body if there are no flaws, like gashes, scratches, or wounds.

2. Oral mucous membrane: If the epithelial layer covering the interior walls of our mouth is healthy, microorganisms cannot infiltrate the blood.

3. Areas around the sexual organs: The sexual organ in males is, even at birth, more protected than that of females. For female children, the epithelium covering the interior face of the organ turns into a multi-layered structure due to the impact of estrogen (sexuality hormone) that starts being secreted after adolescence. That multilayered structure blocks infections that can result from sexual intercourse. Female children before adolescence do not have estrogen, thus their genital organs have a thinner layer of epithelium and are more likely to be infected. This is why cleansing after urination should be done from the front to the back and the genital organs should not come into contact with feces. Our God of infinite mercy also gives girls a hymen in order to protect girls from germs.

B – Flora bacteria (beneficial bacteria): These do not serve as mechanical obstacles, but are assigned tasks. There are some bacteria that do not cause illnesses in the urine and in the proliferation canals, the skin, throat, intestines, and the eyes. Those beneficial bacteria located in our body work for us and hinder other infectious bacteria from settling in these zones. Those places are sterile in the body of a fetus; no beneficial bacteria exist there. Protector bacteria are positioned in those places right after the birth; this is a revelation of God’s infinite compassion. For instance, a baby’s first feces are sterile because there are no bacteria in his intestines. As time passes, a baby adopts protector bacteria through his mouth by nursing, from bottles, and pacifiers. Parents should be careful about the purity of pacifiers, feeding bottles, water, and additional nourishments, particularly in the first couple of months, until the bacteria flora have been established in an infant’s body. Otherwise, babies can easily suffer from diarrhea. God equipped beneficial bacteria with some special peculiarities to be able to deter other microorganisms from settling in the body. Here are some of these peculiarities:

1. They compete with infectious bacteria on the consumption of nutrients, so they restrain the reproduction of other bacteria.

2. They emit bactericides that kill only pathogenic (harmful and infectious) bacteria.

3. Some flora bacteria are assigned a mission to impede the reproduction of pathogenic bacteria so as to reduce pH (increase acidity) in the environment. For example, the lactobacillus in the female genital passage produces lactose by breaking down the glucose in the uterine canal in order to acidify the secreted matters in that canal. Reproduction of fungi is also obstructed in the same way. Due to that fact, some fungal diseases might emerge in genital areas or in the ears, among other places, after antibiotic treatment. Antibiotics kill not only pathogenic bacteria, but also flora bacteria. Thus, desultory usage of antibiotics should be avoided.

Today, beneficial intestinal bacteria are taken orally in capsules, and infectious bacteria in the intestines are killed by supplementing the flora bacteria in that organ without the use of antibiotics.

C – Mechanical cleansing:

1. Secretions:

a.Saliva: Secreted continuously from the glands behind the ears, beneath the chin and beneath the tongue, saliva expels the intruder pathogenic bacteria by cleansing our mouths. It also prevents tooth decay and gum inflammation by cleaning leftover food on which bacteria could feed.

b. Tears: Tears are charged with the duty of cleaning the conjunctiva (the mucous membrane that lines the inner surface of the eyelids and that continues over the forepart of the eyeball) and the cornea (the transparent part of the coat of the eyeball that covers the iris and pupil and admits light to the interior).

2.Cilia: These are feather-like cell extensions of microscopic size.

a.Nasal Cilia: Covering the nasal mucous membrane, mucus (a slimy substance) grasps dust particles and microbes in the air due to its adhesive nature. Lumpy folds inside the nose do not let the air flow straight. Therefore, a turbulent air current occurs in the nose. This turbulent current causes the particles in the air to come into contact with this slimy substance and to get stuck there. Epithelial cells also have cilia expanding toward the nasal cavity. Every cell has nearly 200 cilia. These cilia push mucus and the dust particles attached to it toward the pharynx with an up and down whipping action (10–20 strokes per second) so as to keep them away from the lungs.

b.Cilia in the lower respiratory passages: The upper surface of epithelium that is spread on the trachea, bronchi, and bronchioles is also covered with mucus. Epithelial cells in this area have cilia, too. These cilia do the same whipping action to push particles and microorganisms in the mucus toward the pharynx. They are pushed into the pharynx and expelled by coughing. One of the damaging impacts of nicotine on the respiratory system is that it paralyzes these cilia and disrupts the discharging process of harmful particles. As a consequence, smoking leads to many lung diseases.

D – Enzymes, acids and antibodies in body secretions:

1.Lysozyme: This is a substance found in body secretions (saliva, perspiration, tear, genital organ secretion etc.) that kills bacteria.

2.Stomach acid (Hydrochloric acid, HCl): Being emitted through stomach glands, HCl is a strong acid that can destroy bacteria that are able to reach as far as the stomach with the food we eat. Although we usually have our meals without cleaning our hands sufficiently or without washing them thoroughly, we rarely (except for situations where we are exposed to a high density of microbes like food poisoning or dirty drinking water) get infected via this route. The actors in this perfect protection are lysozyme and stomach acid.

3.Antibodies: Being present in the blood and body secretions, antibodies play a role in the defense against microorganisms. Antibodies in breast milk are passed from the mother’s blood to her milk via a very special mechanism, and are significant in the protection of an infant from infections.

E – Defender Cells: Resembling special operation forces, each of these cells is trained in different parts of the body and sent into the blood circulation. Those troop-like cells, which protect us against diseases by struggling fiercely with germs that can reach the blood after overcoming many obstacles, cannot have come about merely by chance, without the participation of the All-Knowing Designer.

1.Macrophages: Monocytes, a kind of leukocyte in the blood, pass from the capillaries to the tissue and turn into giant cells called macrophages that can phagocytose (swallow microbes) at a great rate. Macrophages swallow and tear down every kind of bacteria and virus that invades the body. These cells constitute the first defense line of the body and serve like advance guards. For instance, the first force to start fighting against the germs that can penetrate the skin through a scratch is the macrophages found just beneath the skin are called histiocytes. Germs that can infiltrate the blood through the intestines and reach the liver via the portal vein are eradicated by another type of macrophage. Therefore, almost no bacterium can pass from the intestines into the general blood circulation system. Germs that enter the body orally are destroyed by macrophages stationed in the lymph nodes on the tonsils. The ones that manage to reach the lungs through the respiratory paths are killed by the macrophages in the alveoli. Those cells also cause T-lymphocytes (very specially equipped cells) to proliferate by stimulating them. 2.Neutrophils: These are the most common type (60-70%) of leukocytes. These cells participate only in fights against bacteria. When bacteria enter a tissue, some poisonous matters emitted by them cause a chemical reaction called chemotaxis; this reaction attracts the neutrophils toward the infected tissue. In this case, the neutrophils leave their capillaries for the infected tissue and find and destroy the bacteria. How can germ-eating cells, like macrophages and neutrophils, distinguish normal body cells from microbes? Undoubtedly, the Creator of such an excellent defense system does not make us worry about such a problem; it was for this purpose that God created opsonins. Opsonins are similar to adapters in that they are able to attach two different parts together and connect themselves to a specific place on the germ. Thus, macrophages and neutrophils carry out their germ-eating job perfectly, connecting themselves to those opsonins. Since our own body cells do not have receptors that can handle opsonins, they cannot be eaten. 3.Lymphocytes: These are the troops of the immunity system with the most complicated organizations and strategies. These troops are categorized as T and B lymphocytes. They are the most important and powerful of the immunity mechanisms and constitute about 20-30% of the leukocytes in blood. They are regarded as the last defense line against those germs with which the other mechanisms cannot cope. a.T lymphocytes: When T lymphocytes are stimulated by macrophages, T cells that are a form of T lymphocyte secrete a matter called lymphokine. Lymphokine stimulates cytotoxic (microbe killer) T cells and B lymphocytes into action. Unless auxiliary T cells exist, the acquired immunity system collapses. Likewise, the HIV virus destroys auxiliary T cells and renders a person susceptible to disease. Even very simple infections can turn into a catastrophe for those patients. Cytotoxic T cells assault bacteria and particularly virus-infected body cells. They deliver porphyrins (proteins to make holes) into cell membranes by attaching themselves to the cells. In that way, a huge amount of water enters the cells and they get torn, due to over-swelling. Thus, viruses in the infected cells are dispersed and are neutralized by specific antibodies produced for that purpose with their infecting ability being impeded. (Viruses have to enter body cells to be able to proliferate. Only in this way can they protect themselves against antibodies and proliferate. Viruses that proliferate in cells use matters in those cells and cause them to eventually break apart, then move onto other cells.) b.B lymphocytes: These cells are stimulated directly by microbes. However, they need lymphokines to be completely stimulated and activated. Lymphokines are created capable of causing B lymphocytes to proliferate and transform themselves to Plasmocytes. Plasmocytes also emit antibodies to the blood. c.Killer cells: These play a role in the innate immune system, so they do not need stimulation like T and B lymphocytes. In particular, they assault body cells that are virus-infected or show a tendency to cancer. In this way, they establish a first defense line against viruses and block cancer development. Even though the working principles of lymphocytes are not known, they are related in some way to spiritual values such as love, enthusiasm, and peace of mind. Likewise, it is known that the immune systems of people whose spirituality has been weakened by depression and stress are more susceptible to break down. Unless those people recover by activating their spiritual dynamics, like faith in destiny, they are under a greater threat of cancer. Yet, this world is a place of examination. We cannot claim that every cancer is due to a damaged spirituality; we should not forget that cancer might occur due to different reasons. 4. Eosinophils: These are a kind of leukocytes that can kill some sort of parasites. They cling to parasites and release the granules in their cytoplasm into the parasites. These granules contain enzymes which destroy parasites. 5. Mast cells and basophils: Mast cells and basophils play a central role in inflammatory and immediate allergic reactions. They are able to release potent inflammatory mediators. Mast cells function out of the veins and protect the tissues in the body, whereas basophils are similar cells found in the bloodstream. F – Factors in plasma: 1.Antibodies: These are secreted into the blood by plasma cells. They fight against the germs that have stimulated them. They show their impact directly (neutralizing bacterial poisons, gathering and precipitating bacteria, neutralizing viruses, pulling microorganisms into pieces) or by activating a very special system called a complement. 2.Complement proteins: When inactive complement proteins in plasma are stimulated by antigens and an opposing antibody complex, active complement compounds are brought to life. These compounds have various effects like chemotaxis, opsonization, development of inflammation as a result of stimulation of mast cells and basophils, and the destruction of microorganisms. The complement system can be stimulated by microorganisms without a need for antibody development (without a need for lymphocytes); this can be seen as a manifestation of our Creator”s name Mudabbir (managing, administering, controlling every being in balance and order). This ensures the stimulation of a complement system under conditions that lack antibody production. Hence, the body is never left completely undefended. Is it really possible that such an amazing defense system, that requires unlimited knowledge and power, and that consists of every kind of alternative action, can come into existence by itself? 3.Interferons: Viruses invade body cells and synthesize proteins that contribute to their proliferation. Interferons, secreted by lymphocytes or other leukocytes, are created so that they can attach themselves to virus-infected body cells and obstruct the production of those proteins. Hence, these viruses cannot proliferate. 4.Lysozyme: Mentioned in the earlier part concerning body secretions, lysozyme is also available in the blood and kills bacteria there. 5.Properdin: This is a kind of protein available in the plasma which can neutralize viruses and destroy some bacteria types. 6.Acute phase proteins: These are a large number of serum proteins (C-reactive protein, etc.) that are swiftly synthesized by the liver and that are employed in defense during infections. 7.Beta-lysin: A substance that destroys some types of bacteria. G – Events caused by infections: 1. Inflammation: Inflammation is a response that is designed to protect tissues against tissue destruction, caused by factors like infection, excessive heat, and trauma. When a tissue is invaded by microorganisms, it starts to be destroyed; certain matters come out of those tissue cells (as mast cells) and lead to certain reactions in that zone. a.Vasodilation: As the little veins transporting blood to a tissue widen, more blood rushes in and more neutrophils are carried to that zone. Meanwhile, a color enhancement (blushing) occurs in that place. b.Increase in permeability of the capillaries: Neutrophils can penetrate into the tissues more easily. Plenty of water also passes through tissues, so some edemas (swelling in tissues) develop. Finally, coagulation proteins in the plasma, which can rarely infiltrate from capillaries to the tissues because of their large molecular structures, pass to the tissues and clot the liquid here. Hence, lymph veins, which are responsible for returning the liquid to the blood circulation, are plugged by clots. Consequently, inflammation detains microorganisms in that specific zone and prevents them from spreading throughout the body. Microorganisms are also destroyed by tissue macrophages in the inflammation zone and the migrant neutrophils working there. (The more a bacterium causes tissue damage, the harder it passes to blood.) Then, remnants of dead bacteria, damaged tissue cells, and neutrophils that are also destroyed after the phagocytosing of between 5 and 20 bacteria soften the inflammation by dissolving and creating some pus in that zone. The pus streams out by itself or is relieved by an incision being cut in the covering skin. 2. Fever:Toxins coming out of some bacteria and some secretions of microbe-phagocytosing cells lead to an increase in body temperature. Fever stops reproduction of microorganisms and kills them by ruining their structures. Within this framework, the occurrence of fever is beneficial; it indicates that the body is resisting and struggling to kill the microbes. Therefore, fever should not be reduced as long as it is not too high to cause brain damage (especially for children). 3. Cough: A cough helps the body discharge the microbes in the respiratory paths. Thus, cough medicines should not be used immediately, except in cases of whooping cough. 4. Diarrhea: This helps the body rid itself of feces quickly, so medicines to stop diarrhea should not be used, either. However, in cases of cough and diarrhea, a person should know their own strength and the strength of their immune system well and take medication accordingly. When we consider all these defense mechanisms, this question occurs in our minds: Do we protect ourselves against infections or is there someone who operates various immunity mechanisms in our bodies and controls them at every moment with His infinite knowledge and power?

Mucus is a viscoelastic gel-like material. It has been used to describe the coating and/or lining layers of vertebrates (e.g. fish, mammals) and invertebrates (e.g. coelomates, molluscs) (Rose, 1992). As noted earlier, in mammals the term mucus is restricted to the material covering the epithelial surfaces and providing an interface between the external environment and the epithelial layers. In vertebrates, this interface provides lubrication, maintenance of tissue hydration, and cytoprotection against proteases – a group of enzymes that break down the bonds amoung aminoacids – pH extremes, chemical irritants, and biological agents. Whereas invertebrate mucus has additional biological functions, like navigation, locomotion, and structural support (Denny, 1989). In the human both, the importance of these biological functions may vary depending on the location of the mucus: for example, in the respiratory tract, to clear the airways of inhaled particles: in the eyes, to prevent corneal surfaces from drying: in the reproductive tract, to protect the uterine cavity and control the survival and penetrability of the spermatozoa. However, there is one important function common to all systems, namely the maintenance of the mucosal water balance.

The composition of mucus

It is important to know something about the biological composition of mucus. In humans, this viscoelastic gel usually contains more than 90% water, 0.5-5% high molecular weight glycoproteins, termed mucins, and also a large number of other components such as electrolytes, lipids, plasma proteins and nucleic acids. Mucins are extremely large and heavily glycosylated molecules that consist primarily of a non-globular, thread-like polypeptide backbone and 0-linked oligosaccharide side chains. Within the mucin producing cells the molecules are found, without water, within large membrane-bound granules that fill the upper part of the cell. It appears likely that the mucins are the major determinants of mucus behaviour, and non-mucin constituents such as DNA, lipids and proteins are, when present, likely to influence the properties of the gel (Carlstedt, 1988). However, acidic mucopolisaccharides and glycoproteins are the major macro- molecular components of mucus in other animals, such as marine snail mucus (Rose, 1992).

In general, the gel forming mucin macromolecules have an oligomeric structure and are assembled from subunits via disulphide bonds. They can be fragmented into subunits by reduction of these disulphide bonds (Thornton. 1995). On the basis of their sensitivity to proteases it is believed that mucins typically contain two different types of domains that are highly glycosylated regions (rich in serine and threonin) and ‘naked’ hydrophobic regions that have lower substitution with carbohydrates. Where when and how does such a complex substance get synthesized, assembled and secreted? And what can happen if the process goes wrong or gets out of balance?

In the gastrointestinal tract

One of the common places where mucus has many vital functions is the gastrointestinal tract. The main site of production of intestinal mucin is the goblet (mucous) cell. However; there is a small amount of mucus production in columnar cells (intestinal epithelial cell). Mucus secretion is probably under both neural and hormonal control. However, little is known about exocytosis in which the membrane of the granules fuses with the apical plasma membrane, thereby releasing its contents.

In this tract, mucus forms a protective layer between the epithelial surface and the luminal compartment, and has been indicated in the mechanical protection of the gastrointestinal epithelial cells from bile acids, pH extremes, digestive enzymes, biological agents such as bacteria, virus and parasites, and mechanical damage. Also, in the stomach, mucus provides a mixing and diffusion harrier which protects the stomach wall from the damaging effects of the secreted hydrochloric acid which plays a big part in the digestion of our food. Bicarbonate ions are secreted into the unstirred mucus layer to help neutralize the acid and limit its harmful effects (Flemstrom, 1987). We are unaware of this function of mucus generally; however, when someone has a stomach or duodenal ulcer, or any types of gastritis, they have to take some anti- acidic drugs and so become aware of their neutralizing mucus blanket.

We know little about the involvement of gastrointestinal mucus in disease. It is suggested that there is a selective loss of a ‘specific’ mucin subpopulation in ulcerative colitis which is an inflammatory intestinal disease (Podoisky & Isselbacher, 1984). Many recent studies indicate that mucins secreted by colorectal carcinoma are immunologically and biochemically different from those in normal colon and adenomatous colon in which there is epithelial benign tumour and/or tumours in the colorectum (Gendler eta1., 1990; lass et al., 1994). Moreover, it has been shown that some components of mucus can be employed as a marker for colonic carcinoma and pre-cancerous conditions (Guang & Abdulkalam. 1995).

In the respiratory tract

Another common place for mucus is the respiratory tract, where mucus is produced by submucosal glands and by goblet cells interspersed among the ciliated respiratory epithelial cells. The cilia are like tiny hairs and are very numerous on epithelial cells of the upper respiratory tract. There maybe 250 or more cilia on the surface of a ciliated epithelial cell, arranged in regular rows. The ciliated epithelial cells, together with a thin mucus layer, constitute the mucociliary transport system designed to clear the airways from foreign particles such as dust, pollen, bacteria or other harmful particles. When we inhale these harmful particles into the lungs, a local stimulation of mucus secretion is evoked. The mucus blanket surrounds the particle and is moved by the cilia which beat in a rhythmical, wave-like manner into the trachea and from there it is swallowed to the gastrointestinal tract. In this propelling the gel towards the pharynx (the upper part of the trachea), the tips of the cilia interact with the mucus layer so that the energy can be passed from the cilia to the mucus blanket. If something goes wrong with the ciliated epithelium or the epithelium is depleted of mucus, this transport may not necessarily occur.

Although in healthy individuals goblet (mucous) cells represent on average 1/10 of ciliated cells, in a chronically obstructed airway (when diseases such as bronchitis, asthma, bronchorrhea and cystic fibrosis are present) the number of the goblet cells and of the submucosal glands increases markedly. In these particular diseases, hyperplasia of goblet cells, hypertrophy of submucosal glands and the hypersecretion of mucus are the prominent features of the pathological process. The most common inherited disease where mucus is very important is cystic fibrosis. This disease appears in about 1 in 2000 people born in Europe and America, although 1 in 20 people carry the defective gene. In this case mucus is stickier than normal and so the abnormally sticky mucus cannot be easily removed from the lungs. Instead of acting as the means for removing bacteria, the mucus becomes a breeding medium for them and the complications of the resulting infection ultimately lead to early death. 

In the reproductive tract

Besides the gastrointestinal and respiratory tracts, mucus is very important also in the reproductive tract. The cervical canal, the entrance to the upper reproductive tract, is filled with mucus whose biological functions are to protect the genital tract from infection and to control the survival and penetrability of the spermatozoa (male germ cell). The amount and physical properties of mucus vary during the ovulatory cycle. At ovulation, when the woman produces ova from her ovary, there is an increased hydration of mucus which results in a watery secretion with high spermatozoal penetrability and low viscoelasticity (Wolf et al., 1978). In contrast, during the luteal phase, the second part of the menstrual cycle, the mucus is scant, contains less water and provides an effective barrier to the spermatozoa (Carlstedt et al., 1988). During pregnancy a large mucus plug blocks the cervical canal in order to protect the uterine cavity including the baby from any external effects. If the composition of the mucus changes during the early stages of the pregnancy, this mucus plug may become defective and the pregnancy may result in abortion or premature birth. It has been shown that high levels of cell-surface MUC1 (a mucin gene product) inhibit both cell-cell and cell-matrix adhesion that is important in human embryo implantation and this occurs in the mid-secretory phase of the menstrual cycle (Aplin & Hey, 1995). Moreover, the changing of mucus composition may be an important factor in infertility, because it controls the survival and penetrability of the spermatozoa. Also, there is the same significant alteration in the biochemical characteristics of the mucus in endometrial carcinoma.

Alterations in mucus composition

As mentioned earlier, there are some notable alterations in the biochemical characteristics of mucins in many diseases. For example, in chronic obstructive respiratory disease excess mucus is present in airways. In cancer, one frequently finds abnormal carbohydrate structures on mucins that can serve as surrogate markers for tumour progression. Also, mucin peptide epitopes that are normally covered with carbohydrates become uncovered and can serve as markers. Since membrane mucins can function as anti-cell adhesion molecules, and their over expression in cancer may facilitate tumour dissemination and therefore metastases. However, there is still a lot of work to be done to understand biosynthesis, secretion and functions of the mucus, especially mucins, in healthy people or in diseased conditions. How is it that mucus can change in response to environmental influences, bacterial attack, or hormonal balance? What is the relationship between mucus and the progression of cancer or such kind of life-threatening diseases? It is clear that mucus is susceptible to almost infinite and rapid modification. When we understand how this capability is employed and controlled, we may be one step nearer to controlling sonic life-threatening diseases, such as cystic fibrosis, cancer, or some abnormal conditions, like infertility and miscarriage.

As a conclusion we can say that mucus may appear a sticky, tiresome, messy nuisance hut it is obvious that a life without mucus would he extremely uncomfortable. It is a gift of the Creator to all living beings, and a miracle, many of whose wonderful mysteries remain to he discovered. 

References

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• Carlstedt I. (1988) Mucus Gylcoproteins: Structure and Macromolecular Properties, Lund University Press, Lund,
• Denny M.W, (1989) ‘Intervertebrate mucus secretions: functional alternatives to vertebrate paradigms’. Symp. Soc. Exp. hal. 43, p. 337.
• Flemstrom (3. (1987) Physiology of Gastrointestinal Tract, Raven Press, New York, pp. 1011-29.
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• Podolsky D. & Isselbacher K.J. (1984) Gastroenterology, 87, pp.99 1-8. Rose MC. (1992) ‘Mucins: structure, function, and role in pulmonary diseases’. The Am. Physiol. Soc., pp. L413-L429.
• ThorntonD.J., Howard M., Devine P.L.,. Sheehan J.K. (1995) ‘Methods for separation and deglycosylation of mucin subunits’. Analytic Biochemistry. 227, pp.162-7.
• Wolf DR Blasco L., Khan M.A., Litt M. (1978) , Fertil. Steril. 30, pp.163-9