Pre-auditory self-work materials.
3.1.Basic knowledge, skills, experiences, necessary for study the topic:
| Subject | To know | To be able to |
| Biology and Medical Genetics | Inheritance main ways | Analyze primary immunodeficiencies inheritance ways |
| Pathophysiology | Leucopenies, leucocytoses, immunodeficiencies reasons and developmental mechanisms | Interpret leucocytic formule to say in part about leucocytic gap, acute and chronic leucoses |
| Pediatry with Neonatology | Leucocytes, specific and unspecific defense mechanisms peculiarities in children of different age | Say about leucocytes, organism defensive mechanisms pathology |
| Internal Diseases | Different leucocytic sets functions, leucocyte formule, specifc and non-specific defencive mechanisms | Tell about ethiology, pathogenesis, treatment and prophylaxy of leucopenies, leucocytoses, immunodeficiencies |
| Immunology | Different leucocytic sets functions, leucocyte formule, specific and non-specific defensive mechanisms, immunogram major indexes | Tell about ethiology, pathogenesis, treatment and prophylaxy main primary and secondary immunodeficiencies |
3.2. Topic content
White blood cell (WBC) or leukocyte is the colourless and nucleated formed element of blood. Leukocytes play very important role in defense mechanism of the body. Depending upon the presence or absence of granules in the cytoplasm, the leukocytes are classified into 2 types namely:
1. Granulocytes—with granules and
2. Agranulocytes—without granules.
The granulocytes are neutrophils, eosinophils and basophils. Agranulocytes are monocytes and lymphocytes (Fig. 6).
MORPHOLOGY OF WHITE BLOOD CELLS
NEUTROPHILS
Neutrophils or polymorphs have fine or small granules in the cytoplasm. The granules take acidic and basic stains. So, the granules appear violet in colour after staining. The nucleus is multi-lobed. The number of lobes in the nucleus depends upon the age of cell. In younger cells, the nucleus is not lobed. And in older neutrophils, the nucleus has 4 or 5 lobes. The diameter of cell is 10 to 12 microns. The neutrophils are ameboid in character.
EOSINOPHILS
Eosinophils have coarse (larger) granules in the cytoplasm, which stain bright red, or orange with eosin. The nucleus is bi-lobed. The diameter of the cell varies between 10 and 14 microns.
BASOPHILS
Basophils also have coarse granules in the cytoplasm. The granules stain purple blue with basic dyes like methylene blue. Nucleus is bi-lobed. Diameter of the cell is 8 to 10 microns.
|
|
|
MONOCYTES
Monocytes are the largest leukocytes with diameter of 14 to 18 microns. The cytoplasm is clear without granules. The nucleus is round, oval, horseshoe or kidney shaped. The nucleus is either in the center of the cell or it is pushed to one side and a large amount of cytoplasm is seen.
LYMPHOCYTES
The lymphocytes also have clear cytoplasm without granules. The nucleus is oval or kidney shaped occupying the whole of the cytoplasm.
Depending upon the size, the lymphocytes are divided into two groups as:
1) Large lymphocytes—the younger cells with a diameter of 10 to 12 microns.
2) Small lymphocytes—the older cells with a diameter of 7 to 10 microns.
Depending upon the function, the lymphocytes are divided into 2 types as:
T lymphocytes—concerned with cellular immunity. B lymphocytes—concerned with humoral immunity.
FIGURE 6: Different white blood cells
NORMAL COUNT OF WHITE BLOOD CELLS
1. Total WBC count (TC): 4,000 to 11,000 /cu. mm of blood
2. Differential WBC count (DC): Given in the Table 3.
Table 3. Normal values of different white blood cells
| Leukocyte | Percentage Absolute value per cu. mm | |
| Neutrophils | 50 to 70 | 3000 to 6000 |
| Eosinophils | 2 to 4 | 150 to 450 |
| Basophils | 0 to1 | 0 to 100 |
| Monocytes | 2 to 6 | 200 to 600 |
| Lymphocytes | 20 to 30 | 1500 to 2700 |
VARIATIONS IN THE COUNT OF WHITE BLOOD CELLS
Increase in leukocyte count is known as leukocytosis. Decrease in leukocyte count is known as leukopenia. The term leukopenia is generally used for pathological conditions only.
PHYSIOLOGICAL VARIATIONS – physiological leucocytosis
1. Age: In infants, the white blood cell count is about 20,000 per cu mm and in children, it is about 10,000 to 15,000 per cu mm of blood.
2. Sex: The white blood cell count is slightly more in males. In females, the leukocytes count is increased during menstruation, pregnancy and parturition.
3. Diurnal variation: The cell count is minimum in early morning and maximum in the evening
|
|
|
4. Exercise: The white blood cell count is increased slightly during exercise.
5. Sleep: During sleep, the white blood cell count is minimal.
6. Emotional conditions: During emotional conditions like anxiety, the count is increased.
7. Pregnancy: During pregnancy, the leukocyte count is increased.
8. Food taking: especially after proteinic food taking that is explained by its antigenic character.
9. Ovulation: insignificant leucocytosis (neutrophyly) at simultaneous eosinophils amount lowering.
10. Fits: up to 20000 and more independently on reasons.
11. Sharp changing of environmental temperature
PATHOLOGICAL VARIATIONS
All types of leukocytes do not share equally in the increase or decrease in the total leukocyte count. In general, the neutrophils and lymphocytes vary in opposite directions.
Leukopenia
The decrease in the total white blood cell count occurs in the following pathological conditions:
1. Anaphylactic shock
2. Cirrhosis of liver, viral hepatitis in acute phase
3. Disorders of spleen
4. Pernicious anemia
5. Typhoid and paratyphoid and
6. Viral infections: measles, rubeole, influenza
7. Chemicals action (benzol)
8. After irradiation
9. Hypoplastic and aplastic processes
10.Medicines (amidopyrinum, butadionum, rheopyrinum, sulphanilamides, cytostatics)
10.Endocrine diseases (acromegaly, thyroid pathology)
11.Leucoses (cytostatics overdosage)
12.New-formations metastazing in bone marrow
Lymphocytopeny
1. Primary immune pathology (different-typed agammaglobulinemy, tymome)
2. Blood system pathology (aplastic anemias, leucosis)
3. Kushing's syndrome
4. Kidney insufficiency
5. AIDS – specific symptom
6. Irradiation
7. Corticosteroid therapy and alkylic drugs taking
8. Hard edemas
9. Systemic red lupus
10. Purulent inflammation
11. Tuberculosis
Neutropeny
1. Viral infections
2. Chronic infections
3. After cytostatics taking
4. Irradiation
5. Aplastic and vitamin B12-deficient anemias
6. Agranulocytosis
Leukocytosis
Leukocytosis occurs in the common pathological conditions like:
|
|
|
1. Infections (pneumonia, sepsis, meningitis, erysipeloid): leucocytosis absence in infectious process acute phase is considered to be unfavorable diagnostic criterium especially at combination with so-called leucocytic formule shift to the left – see below
2. Allergy
3. Common cold
4. Tuberculosis and
5. Glandular fever
6. Nausea and vomiting – with primarily neutrophils amount increasing
7. Inflammatory processes in part at their purulent character
8. Different organs (myocardium, lungs, spleen, kidney) infarction
9. Vast burnings
10.Bleedings
11.Malignant diseases
12.Blood system diseases (leucosis, polycytemy, lymphogranulomatosis)
13.Infectional mononucleosis and lymphocytosis
14.Uremia
15.Diabetic coma
16.After splenectomy (expressed leucocytosis 15…20 x 109/l with neutrophyly up to 90%)
However, different leukocyte count is increased in specific diseases as given below.
Neutrophilia
The increase in neutrophil count is called neutrophilic leukocytosis. This occurs in the following conditions:
1. Metabolic disorders
2. Injection of foreign proteins
3. Injection of (foreign) vaccines
4. Poisoning by chemicals and drugs like lead, mercury, camphor, benzene derivatives, etc.
5. Poisoning by insect venom and
6. After acute hemorrhage.
Eosinophilia
The increase in eosinophil count is called eosinophilia and this occurs in:
1. Allergic conditions
2. Asthma
3. Blood parasitism (malaria, filariasis) and ascaridosis
4. Intestinal parasitism and
5. Scarlet fever
6. Tumors
7. Lymphogranulomatosis
8. Chronic myeloleucosis
9. Medicines (antibiotic, sulphanilamides in part)
Basophilia
Increase in basophil count is called basophilia and it occurs in:
1. Smallpox
2. Chicken pox and
3. Polycythemia vera
4. Allergic processes accompanied by rash
5. Before and during menstrual bleeding
6. Stress
7. Leucosis
8. Myocardial infarction
Monocytosis
Increase in monocytes count is known as monocytosis and occurs in:
1. Chronic infections (tuberculosis, syphilis, brucellosis)
2. Acute infections (rubeole, scarlet fever, infectious parotitis, mononucleosis)
|
|
|
3. Lymphogranulomatosis
4. Endocardites
5. Helminthes
Limphocytosis
1. Increase in lymphocyte count is called lymphocytosis and this occurs in:
2. Diphtheria
3. Infectious hepatitis
4. Mumps
5. Malnutrition
6. Rickets
7. Syphilis
8. Thyrotoxicosis and
9. Tuberculosis
Leukemia
The leukemia is the condition, which is characterized by abnormal uncontrolled increase in leukocyte count up to 1,000,000/cu mm.
LIFESPAN OF WHITE BLOOD CELLS
Lifespan of white blood cells is not constant. It depends upon the demand in the body and their function. Lifespan of these cells may be as short as half a day or it may be as long as 3-6 months.
However, the normal lifespan of white blood cells is as follows:
| Neutrophils — | 2-5 days |
| Eosinophils — | 7-12 days |
| Basophils — | 12-15 days |
| Monocytes — | 2-5 days |
| Lymphocytes — | 1 day |
Table 4. White Blood Cells Lifespan
PROPERTIES OF WHITE BLOOD CELLS
1. Diapedesis
Diapedesis is the process by which the leukocytes squeeze through the narrow blood vessels.
Ameboid Movement
Neutrophils, monocytes and lymphocytes show amebic movement by protruding into the cytoplasm and changing the shape.
3. Chemotaxis
A number of chemical substances in the tissues cause the leukocytes to move towards tissues. This phenomenon is called chemotaxis.
4. Phagocytosis
Neutrophils and monocytes swallow foreign bodies by means of pseudopodia.
FUNCTIONS OF WHITE BLOOD CELLS
NEUTROPHILS - are produced in bone-marrow, live 8-10 hours, part of them are in circulation, another one – into marginal state and significant part leaves blood and dies in tissues.
Neutrophils play an important role in the defense of the body. Along with monocytes, the neutrophils provide the first line of defense against the invading microorganisms. The granules of neutrophils contain enzymes like proteases, myeloperoxidases, elastases and metalloproteinases. The granules also contain antibody like substances called defensins. Defensins are antimicrobial peptides, which are active against bacteria and fungi. Neutrophils also secrete platelet activating factor (PAF) which accelerate the aggregation of platelets during injury to the blood vessel.
Mechanism of Action of Neutrophils
Neutrophils are released in large number from the blood at the time of infection by the foreign microorganisms. At the same time, new neutrophils are produced from the progenitor cells. All the neutrophils move by diapedesis and are attracted towards the site of infection by means of chemotaxis. The chemotaxis occurs due to the attraction by some chemical substances called chemo-attractants, which are released, from the infected area. After reaching the area, the neutrophils surround the area and get adhered to the infected tissues. The chemo-attractants increase the adhesive nature of neutrophils so that all the neutrophils become stickier and get attached firmly to the infected area. Now, the neutrophils start destroying the invaders. First, these cells engulf the bacteria and then destroy them by means of phagocytosis. Each neutrophil can hold about 15-20 microorganisms at a time. During the battle against the bacteria, many leukocytes are also killed by the toxins released from the bacteria. The dead cells are collected in the center of infected area. The dead cells together with plasma leaked from the blood vessel, liquefied tissue cells and red blood cells escaped from damaged blood vessel (capillaries) constitute the pus. The dead white blood cells are called the pus cells.
Functions:
· participating in phagocytosis;
· apoptosis triggering;
· interleukines-1,6,8 and 12 formation;
· interpheron formation;
· immune reactions;
· participation in mitosis;
· reparational and regenerational processes;
· hematopoietic reactions;
· blood coagulation;
· fibrinolysis (they contain plasminogen activator).
EOSINOPHILS - are produced in bone-marrow, live from 4 to 12 days. They are only several hours in blood stream, then penetrate into the tissue for destruction.
Functions:
· phagocytosis;
· antitoxic function;
· kallikrein-kinin system components activation.
Eosinophils are specifically meant for acting against the parasites. The eosinophil count increases during parasitic infestations and allergic conditions. Rose sundown of speedy recovery after infectious pathology - eosinophyly – is a very favorable and long-awaited diagnostic criterium. Eosinopeny – their amount decreasing - is observed at hard infectional diseases – unfavourable diagnostic sign.
Mechanism of Action of Eosinophils
The eosinophils are neither markedly motile nor phagocytic like the neutrophils. But their granules contain mar, substances, which become cytotoxic when released during the invading organisms. Following are the lethal substances present in the granules of eosinophils and release; at the time of exposure to parasites or foreign proteins
1. Eosinophil peroxidase: This enzyme is capable destroying helminthes (worms), bacteria and turned cells.
2. Major basic protein (MBP): This is very active against helminthes. It can damage the parasites by distension (ballooning) and detachment of the tegmental sheath (skin like covering) of these organism
3. Eosinophil cationic protein (ECP): This substances the major destroyer of helminthes. It destroys the parasite by means of complete disintegration. It is also acts as neurotoxin.
4. Eosinophil derived neurotoxin: it destroys the nerve fibers particularly the myelinated nerve fibers.
BASOPHILS - are formed in bone-marrow, live up to 12 hours. Their relatives - fat cells (mast cells, mastocytes) live for years.
The basophils play an important role in healing process after inflammation and in acute hypersensitivity reactions (allergy). The number of basophils is increased during healing process and right before menstruation (especially in sexual organs vessels).
Mechanism of Action of Basophils
The functions of basophils are executed by the releasing of some important substances from their granules.
1. Histamine: It produces the acute hypersensitivity reactions by causing vascular changes and by increasing the capillary permeability.
2. Heparin: Heparin is essential to prevent the intravascular blood clotting.
3. Hyaluronic acid: This is necessary for deposition of ground substances in the basement membrane. It participates in membrane permeability increasing.
4. Proteases and myeloperoxidase: These enzymes may exaggerate the inflammation responses.
5. Platelets activation factor synthesis.
6. Thromboxanes production – see next lection.
7. Leucotryens – participate in multiple organism reactions.
8. Prostaglandines – the same + next lecture.
The basophils also have IgE receptors, which het; them to produce hypersensitivity responses.
It is necessary to mention that eosinophils can reduce allergy reactions because they contain histaminase – histamine-decomposing enzyme. There is so-called eosinophylic-basophylic association – parallel increase of basophils and eosinophils. It can be observed at allergy latest stages. And if it is so – it is considered as a favorable prognostic criterium for the patient.
Mast Cell
Mast cell is a large tissue cell resembling the basophil is present in bone marrow and around the cutaneal blood vessels but does not enter the circulation.
The mast cell plays an important role in producing hypersensitivity reactions like allergy and anaphylaxy. It secretes heparin, histamine, serotonin, and hydrolytic enzymes.
MONOCYTES – are formed in different hemopoietic organs:
· bone marrow,
· lymphatic nodes;
· connective tissue.
Life duration – 36-104 hours. They leave tissues and form macrophagal family there.
Role:
· strong phagocytosis;
· contain monokines influencing on lymphocytes;
· antiinfectional action;
· antitumorogenic activity;
· blood coagulation;
· fibrinolysis;
· complement system components synthesis.
Monocytes play an important role in defense of the body. Along with neutrophils, these leukocytes constitute the first line of defense. Like neutrophils, the monocytes are also motile and phagocytic. The monocytes are the free cells in the body and wander freely through the tissue. Like neutrophils, practically no part of the body is spared by monocytes.
Monocytes secrete interleukin-1 (IL-1), colony stimulating factors (CSF) and platelet activating factor (PAF).
Monocytes are the precursors of the tissue macrophages. The matured monocytes stay in the blood only for few hours. Afterwards these cells enter the tissues from the blood and become tissue macrophages. Examples of tissue macrophages are Kupffer cells in liver, alveolar macrophages in lungs and macrophages in spleen.
LYMPHOCYTES
The lymphocytes play an important role in immunity. Functionally, the lymphocytes are classified into two categories namely, T lymphocytes and B lymphocytes. T lymphocytes are responsible for the development of cellular immunity and B lymphocytes are responsible for the development of humoral immunity. T-lymphocytes are thymus-dependent. Their processing in thymus occurs mostly during the period between just before birth and few months after birth. Thymosin is a hormone secreted by thymus and released into circulation. Thymosin also plays an important role in immunity. It accelerates the proliferation and activation of lymphocytes in thymus. It also increases the activity of lymphocytes in lymphoid tissues.
There one of their population comes to thymus where their differentiation in T-lymphocytes takes place. Other part – to bursa of Fabricius analogue (in birds) in small intestine cellular formations, tonsills, appendix, bone marrow and are differentiated in lymphocytes (bursa-dependent). The bursa of Fabricius is a lymphoid organs situated near the cloaca of birds. The bursa is absent in mammals, and the processing of B lymphocytes takes place in bone marrow and liver. This lymphocytic part is not differentiated in immune organs and such lymphocytes are called zero-lymphocytes (neither T-, nor B-).
T-lymphocytes have several types:
· helpers or inducers;
· cytotoxic or killers;
· suppressors;
· memory.
In a whole, they are responsible for cellular immunity. Their amount is 40-70 per cent of all lymphocytes amount.
Storage of T Lymphocytes
After the transformation, the various types of T lymphocytes leave the thymus, migrate and stay in the lymphoid tissues present in lymph nodes, spleen, bone marrow and the gastrointestinal tract.
B-lymphocytes also have several types:
· plasma cells;
· memory cells.
According to another classification – subsets like T-lymphocytes.
They provide immunoglobulins formation (B-lymphocytes are transformed into plasmocytes – producers of these molecules) and thus delt with cellular and especially with humoral immunity. Their amount is 20-30 per cent of all lymphocytes.
Storage of В Lymphocyte
After the transformation, В lymphocytes migrate and stay in the lymphoid tissues present in lymph nodes, spleen, bone marrow and the gastrointestinal tract.
Zero-lymphocytes secrete proteins (perphorines) possessing the ability to make the foramen in side cells membrane and while protheolytic enzymes (cytolysines) pouring in them destroy them. That’s why they are often named as natural killers. Their amount is 10-20 per cent of all lymphocytes.
Leucocytic formula:
· basophils – 0-1,0 %;
· eosinophils – 1,0-4,0 %;
· neutrophils - 50,0-70,0 % - among them:
· juveniles – up to 1,0%,
· rod or stab neutrophils (rods or stabs) – 1,0-4,0 %,
· segs or segment-nuclear neutrophils – 50,0-65,0 %;
· lymphocytes – 25,0-40,0 %;
· monocytes – 2,0-10,0%.
Movement (shift) to the left - is called regenerative movement (blood renewal, sign of so-called young blood); is characterized by juveniles and rod (stab) neutrophils increasing in blood. Reasons:
· infectional diseases;
· leucoses;
· inflammational processes.
Movement (shift) to the right - is called degenerative movement (sign of old blood): is characterized by juveniles and rod (stab) neutrophils amount decreasing and segment- nuclear leucocytes number increasing. It may be observed at:
· aplastic anemias;
· leucoses.
LEUCOPOIESIS REGULATION
Like erythropoiesis regulation it can be performed both specific and non-specific ways. Specific way – is leucopoietins action (they are produced into liver, spleen, thymus, kidneys). Their action mechanism is in involving into bone marrow cells differentiation process. Non-specific way – is:
a) vitamin’s action (especially of groups “B12” and “C”);
b) hormones:
· ACTH;
· thyroid;
· sexual;
c) microelements;
d) leucocytes, tissues, toxin’s, microbes metabolic products have special importance for leucopoiesis regulation. The more leucocytes are destroyed, the more new forms are formed.
FIGURE 7: Leucopoiesis
The committed pluripotent stem cell gives rise to colony forming unit and lymphoid stem cell.
COLONY FORMING UNIT
Different colony forming units are:
1. Colony forming unit—Erythrocytes (CFU-E)
2. Colony forming unit—Granulocytes and Monocytes (CFU-GM)
3. Colony forming unit—Megakaryocytes (CFU-M)
DEFINITION AND TYPES OF IMMUNITY
Resistance of the body against the pathogenic agents is known as immunity. It is the ability of the body to resist different types of foreign bodies like bacteria, virus, toxic substances, etc. which enter the body. Immunity is of two types namely, innate immunity and acquired immunity.
INNATE IMMUNITY
Innate immunity is otherwise called natural immunity. It is present from birth and it is the inborn capacity of the body to resist the entry of microorganisms into the body. By chance, if the organisms enter the body, innate immunity eliminates them before they cause any disease. This type of immunity represents the first line of defense against any pathogens. Therefore, it is also called nonspecific immunity. Some mechanisms involved in this type of immunity are as follows:
1. Activities of white blood cells and tissue macrophages, which destroy the foreign bodies by means of phagocytosis
2. The enzymes of gastrointestinal tract and the acid is stomach, which destroy the toxic substances or organisms entering digestive tract through foods
3. Lysozyme and some polypeptides, which destroy or inactivate the bacteria.
ACQUIRED IMMUNITY
Acquired immunity is the resistance developed in the body against any specific foreign body like bacteria, viruses, toxins, vaccines or transplanted tissues. So, this type of immunity is also known as specific immunity. This is the most powerful immune mechanism that protects the body from the invading organisms or toxic substances. Lymphocytes are responsible for acquired immunity (Fig. 8).
Main white blood cell function is to participate in defense organism reactions against foreign agents. There exist the natural (non-specific) and specific defense forms.
The non-specific defense is directed to any foreign agent eliminating. The phagocytosis, the complement system and others humoral defense factors are the main types of such reactions. Phagocytosis consists of engulfing the microbes and cells via the formation of the pseudopods followed by endocytosis of the phagocytic vesicle. Next, the endocytotic vesicle is incorporated into the lysosomes of the phagocytes where the microbes and cells are digested by lysosomal enzymes.Thisphenomenon is adequate to the neutrophiles, monocytes, eosinophiles, macrophages and thrombocytes. In the course of the phagocytosis process we differentiate such stages as the phagocyte approaching to the phagocytized object (or ligand), the ligand contact with the phagocyte membrane, the ligand engulfing, digestion and destruction of the phagocytized object. The phagocytes find their way to the site of injury by chemotaxis or similar guiding mechanisms.
FIGURE 8: Schematic diagram of acquired immunity
Complement system - is a special enzyme system consisting of the proteins (more than 20 types). In includes 9 components (C1…C9). During the activation process some of its components are cleaved in the fragments influencing directly the course of specific and nonspecific defense reactions. There exist the classical and alternative ways of complement system activation. The destruction of foreign and old cells, the phagocytosis and the immune reactions course activates, the vessel wall permeability increases, the blood coagulation hastens at the complement system activation that influence the pathological process.
The other humoral defense factors – defense reactions connected with the action of such substances as lysozyme and interferon. Lysozyme as a protein possesses the enzyme activity suppressing the growth and the development of causative agents and destroying some of the microorganisms. It can be found in nasal mucosa, intestines, salivary secret, lacrimal fluid etc. In small amounts one can find it in the granules of polymorphonuclear leukocytes, in macrophages and when destroyed they fall into the extracellular fluid. Interferon as the globulin of blood plasma can be located in the lymphocytes providing antiviral defense and delaying the cancer cell growth.
Specific defense – immunity – is a reaction complex directed to maintaining the homeostasis on meeting the host’s body with the antigens which are considered as foreign (despite their forming in the organism itself or if they come into it from outside). Under the action of antigen the host body forms the antibodies, activates lymphocytes and thus they get the ability to participate in the immune response. This antigen ability to cause the specific immune response is due to the presence of multiple determinants on its molecule. The active centers of forming antibodies specifically correspond to the determinants like the key to the lock. The antigen interacting with its corresponding antigen forms the immune complex.
The immune organs are divided into central (thymus, bursa of Fabricius, bone marrow) and the peripheral (lymphatic nodes, spleen etc.). There are two categories of acquired immune responces – humoral or antibody-mediated and cell-mediated.
Acquired immunity developed by the entrance of any foreign body or a vaccine is called active immunity.
Types of Acquired Immunity
Two types of acquired immunity:
1) Cellular immunity and
2) Humoral immunity
Cellular Immunity
The cellular immunity is by the activation of T-lymphocytes, which destroy the organisms, entering the body. This is also called cell mediated immunity or T-celled immunity. This is the major defense mechanism against infections by viruses, fungi and few bacteria like tuberculosis bacillus. Cellular immunity is also responsible for delayed allergic reactions and the rejection of tissues transplant from other's body.
Humoral Immunity
Humoral immunity is by the activation of В lymphocytes. This is also called В cell immunity. В lymphocytes actagainst the invading organisms by secreting antibodies into the blood and lymph. The blood and lymph are body fluids (humors) and the В lymphocytes provide immunity through humors. Therefore, this type of immunity is called humoral immunity. This plays an important role in defense mechanism against the bacterial and viral infections.
ANTIGENS
DEFINITION AND TYPES
The antigens are the substances, which induce specific immune reactions in the body. Antigens are of two types. Those present on the body's own cells are called the auto-antigens or self antigens. The antigens entering the body from outside are known as foreign or non-self antigens.
NON-SELF ANTIGENS
Following are the non-self antigens:
1. The receptors on the cell membrane of microbial organisms such as bacteria, viruses and fungi
2. The toxins from microbial organisms
3. The materials from transplanted organs or incompatible blood cells and
4. Allergens or allergic substances like pollen grains.
The non-self antigens are classified into two types depending upon the response developed against them in the body.
1. The antigens, which induce the development of immunity or production of antibodies (immunogenicity)
2. The antigens, which react with specific antibodies (allergic reactivity).
CHEMICAL NATURE OF THE ANTIGENS
The antigens are mostly the conjugated proteins like lipoproteins, glycoproteins and nucleoproteins.
DEVELOPMENT OF CELL-MEDIATED IMMUNITY
INTRODUCTION
The cell mediated immunity is carried by the T lymphocytes. It develops when an antigen or the antigenic material from the invading microbial or nonmicrobial cells is exposed to the T lymphocytes. The exposure or presentation of antigen to the lymphocytes is an important process during development of immunity (immunogenicity). It is carried out by some special type of cells called antigen presenting cells.
ANTIGEN PRESENTING CELLS
There are two types of antigen presenting cells in the body.
1. Macrophages and
2. Dendritic cells
1. Macrophages
The macrophages are the large phagocytic cells, which digest the invading organisms to release the antigen. The macrophages are present along with lymphocytes in almost all the lymphoid tissues.
2. Dendritic Cells
The dendritic cells are nonphagocytic in nature. Three types of dendritic cells are involved in this.
1) Dendritic cells in spleen, which trap the antigen in blood
2) Follicular dendritic cells in lymph nodes which trap the antigen in the lymph and
3) Langerhans' dendritic cells in skin, which trap the organisms coming in contact with body surface.
Дата добавления: 2018-09-22; просмотров: 733; Мы поможем в написании вашей работы! |
Мы поможем в написании ваших работ!