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Body defense mechanism& Immunity

Shrooti Shah

M.Sc. Nursing

Batch 2011

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Objectives

1. Define immunity

2. Classify immunity

3. Explain mechanisms of natural and acquired immunity

4. Discuss the response to invasion by microorganisms.

5. Describe abnormal immune response

6. Discuss nursing process related to immune system

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Immunity• The term immunity refers to the body’s specific

protective response to an invading foreign agent or organism.

• The human body has the ability to resist almost all types of organisms or toxins that tend to damage the tissues and organs. The capability is called immunity.

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Types of immunity

1. Natural (Innate) immunity

2. Acquired (adaptive) immunity

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Natural and acquired immunity

Natural immunity

1. Is a nonspecific immunity present at birth

2. responses to a foreign invader are very similar from one encounter to the next.

Acquired immunity

1. Specific immunity develops after birth

2. Increases in intensity with repeated exposure to the invading agent.

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Natural (Innate immunity)

• The basis of natural defense mechanisms is the ability to distinguish between friend and foe or self and non-self.

• Such natural mechanisms include 1. Physical and chemical barriers– Skin and mucous membrane– Antimicrobial substance in body secretions

2. The action of WBCs

3. Inflammatory response.

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Physical and chemical barriersSkin and mucous membrane

• When skin and mucous membrane are intact and healthy they provide a physical barrier to invading microbes.

• Sebum and sweat secreted on to the skin surface contains antibacterial and antifungal substances.

• Hairs in the nose acts as a coarse filter.

• One way flow of urine from the bladder during micturation

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Antimicrobial substance in body secretions

1. Hydrochloric acid in gastric juice

2. Lysosomes

3. Saliva

4. Immunoglobulin in nasal secretions and saliva

5. Interferons

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White blood cell action

• WBCs participate in both the natural and the acquired immune responses.

• Granulocytes include neutrophils, eosinophils and basophils.

• Nongranular leucocytes include monocytes or macrophages and lymphocytes.

• Lymphocytes consisting of B cells and T cells, play major role in humoral and cell mediated immune responses.

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Inflammatory response

• Major function of the natural (non specific or innate) immune system.

• Chemical mediators assist this response by minimizing blood loss, walling off the invading organism, activating phagocytes and promoting formation of fibrous scar tissue and regeneration of injured tissue

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Dysfunction of the natural immune system

• Immunodeficiency

• Persistent inflammatory response

• Autoimmune bodies

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Acquired immunity• Usually develops as a result of prior exposure to

an antigen through immunization or by contracting a disease.

• Weeks or months after exposure to the disease or vaccine, the body produces an immune response that is sufficient to defend against the disease upon re-exposure to it.

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Active and passive immunity1. Active immunity: Active immunity means that

the individual has responded to an antigen and produced his own antibodies, lymphocytes are activated and the memory cells formed provide long lasting resistance.

2. Passive immunity: In passive immunity the individual is given antibodies produced by someone else

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Response to invasion• When the body is invaded or attacked by

bacteria, viruses, or other pathogens, it has three means of defending itself:

1. The phagocytic immune response

2. The humoral or antibody immune response

3. The cellular immune response

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Phagocyte immune response

• The first line of defense

• Involves the WBCs (granulocytes and macrophages), which have the ability to ingest foreign particles.

• Phagocytes also remove the body’s own dying or dead cells.

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Humoral and cellular immune response

• A second response, the humoral immune response (sometimes called the antibody response), begins with the B lymphocytes, which can transform themselves into plasma cells that manufacture antibodies.

• The third mechanism of defense, the cellular immune response, also involves the T lymphocytes, which can turn into special cytotoxic (or Killer) T cells that can attack the pathogens themselves.

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Humoral immune response

1. Before exposure to a specific antigen, the clones of B lymphocytes remain dormant in the lymphoid tissue.

2. On entry of a foreign antigen, macrophages in the lymphoid tissue phagocytize the antigen and then present it to adjacent B lymphocytes.

3. In addition, the antigen is presented to T cells at the same time, and activated helper T cells are formed.

4. Those B lymphocytes specific for the antigen immediately enlarge and take on the appearance of lymphoblasts.

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Humoral immune response cont…

5. Some of the lymphoblasts further differentiate to form plasmablasts, which are precursor of plasma cells.

6. The mature plasma cells then produces gamma globulin antibodies.

7. Other B lymphocytes differentiate into B-lymphocyte clones with a memory for the antigen.

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Primary response and secondary response

Primary response

1. Response for forming antibodies that occur on first exposure to a specific antigen.

2. Appears 1 week after, with weak potency and short life

Secondary response

1. Response that occurs after second exposure to the same antigen.

2. Begins rapidly after exposure to the antigen (often within hours) is far more potent, and forms antibodies for many months rather than for only a few weeks.

Role of antibodies

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Antibodies• The antibodies can inactivate the invading agent in one

of the several ways, as follows:

1. Agglutination: in which the multiple large particles with antigens on their surface.

2. Precipitation: in which the molecular complex of soluble antigen and antibody becomes so large that it is rendered insoluble and precipitates.

3. Neutralization: in which the antibodies cover the toxic sites of the antigenic agent.

4. Lysis: in which some potent antibodies are occasionally capable of directly attacking membranes of cellular agents and thereby cause rupture of the agent.

Types of immunoglobulin

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IgGIgG (75% of total immunoglobulin)

• Appears in serum and tissues (interstitial fluid)

• Assumes a major role in bloodborne and tissue infections.

• Activates the complement system.

• Enhances phagocytosis

• Crosses the placenta

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IgAIgA (15% of total immunoglobulins)

• Appears in body fluids (blood, saliva, tears, breast milk, and pulmonary, gastrointestinal, prostatic and vaginal secretions).

• Protection against respiratory, gastrointestinal and genitourinary infections.

• Prevents absorption of antigens from food.

• Passes to neonate in breast milk for protection.

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IgMIgM (10% of total immunoglobulins)

• Appears mostly in intravascular serum

• Appears as the first immunoglobulin produced in response to bacterial and viral infections.

• Activates the complement system.

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IgD

IgD (0.2% of immunoglobulins)• Appears in small amounts in serum• Possibly influences B-lymphocytes differentiation ,

but role is unclear.

IgEIgE (0.004% of immunoglobulins)

• Appears in serum• Takes part in allergic and hypersensitivity of

reactions• Combats parasitic infections.

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Cellular immune response• These develop gradually over a period of 24 to 48

hours after the second encounter with an antigen.

• T lymphocytes are primarily responsible for cellular immunity.

• Stem cells continuously migrate from the bone marrow to the thymus gland, where they develop into T cells.

• By spending time in the thymus, these cells are programmed to become T cells rather than antibody producing B lymphocytes.

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Cellular immune response cont…• T cells attack foreign invaders directly. Cellular reactions

are initiated by the binding of an antigen with an antigen receptor .

• The T cells then carry the antigenic message, or blue print, to the lymph nodes, where the production of other T cells is stimulated.

• Some T cells remain in the lymph nodes and retain a memory for the antigen. Other T cells migrate from the lymph nodes into the general circulatory system and ultimately to the tissues.

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Types of T cells

1. Helper T cells: • When activated, helper T cells secrete cytokines

that attract and activate B cells, cytotoxic T cells, natural killer cells, macrophages and other cells of the immune system.

• Helper T cells produce different types of cytokines and determine whether the immune response will be the production of antibodies or cell mediated immune response.

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2. Cytotoxic T cells

• Cytotoxic T cells is a direct attack cell that is capable of killing micro-organisms and, at times, even some of the body’s own cells.

• For this reason these are called killer cells.

• Cytotoxic attack the antigen directly by altering the cell membrane and causing cell lysis and releasing cytolytic enzymes and cytokines.

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3. Supressor T cells

• They are capable of suppressing the functions of both cytotoxic and helper T cells.

• It is believed that these suppressor functions serve the purpose of preventing the cytotoxic cells from causing excessive immune reactions that might be damaging to the body’s own tissues.

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Complement system

• Circulatory plasma proteins which are made in the liver and activated when an antibody couples with its antigen, are known as complement.

• Complement has three major physiological functions: a. defending the body against bacterial infection

b. bridging natural and acquired immunity

c. disposing of immune complexes and the byproducts associated with inflammation.

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Complement system

Complement mediated immune response are summarized as:

1. Cytolysis: Lysis and destruction of cell membranes of body cells or pathogens.

2. Isosonization: Targeting of the antigen so that it can be easily engulfed and digested by the macrophages and other phagocytic cells.

3. Chemotaxis: chemical attraction of neutrophils and phagocytic cells to the antigen.

4. Anaphylaxis: activation of mast cells and basophils with release of inflammatory mediators that produce smooth muscle contraction and increased vascular permeability.

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Abnormal immune reactions

1. Antibody mediated

2. Cell-mediated

3. Mixed antibody

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Antibody mediated reactions

• These occur within minutes of exposure to an allergen (antigen).

• The most common manifestations of this type of allergic reaction include: food allergies, childhood eczema, hay fever, extrinsic asthma.

• In these conditions the released chemicals act locally, causing different effects that depend on the site.

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Acute systemic anaphylaxis (anaphylactic shock)

• It is caused by the entry of an allergen into the blood e.g. snake venom, injectable penicillin.

• There are profound effects throughout the body, including generalized vasodilatation, leading to severe hypotension and contraction of smooth muscle in the respiratory tract, causing acute breathing difficulties.

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Other antibody mediated reactions:

• Reaction of antibodies with cells that have antigens on their cytoplasmic membranes may cause the cells to rupture.

• Abnormal reactions to antibody/antibody complexes sometimes result in them adhering to the endothelium of blood vessels causing inflammation and local damage.

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Cell mediated reactions

The antigen include:

1. Intracellular microbes, e.g. those causing tuberculosis, measles, mumps.

2.Some vaccines, e.g. against smallpox.

3.Some metals and compounds that combine with protein in the skin and cause allergic contact dermatitis.

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Mixed reactions

Autoimmune diseases:• Tissue damage and signs of disease as the

body fails to recognize its own tissues. Destruction of the body’s own cells may be either humoral or cell-mediated.

– Thyroid- Hashimoto’s thyroiditis– Stomach- Addisonian pernicious anemia– Cortex of the adrenal gland- addison’s disease.– Pancreas-type I diabetes mellitus

Organ transplantation and rejection

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Nursing processNursing assessment• An assessment of immune function begins with

a health history and physical examination

Health history1. Age

2. Nutrition

3. Infection and immunization

4. Allergy

5. Medications and blood transfusion

6. Lifestyle and other factors

Physical examination

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Nursing management• Assisting with medical measures aimed at

improving immune status and treating infection, improving the nutritional status, and maintaining bowel and bladder function.

• Careful hand hygiene, encouraging the patient to cough and perform deep-breathing exercises at regular intervals, and protecting the integrity of the skin and mucous membranes.

• Use strict aseptic technique when performing invasive procedures

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Nursing management cont…

• Assisting the patient in managing stress and in adopting a lifestyle that enhances immune system function.

• The patient or parents (if the patient is a child) must be informed about the potential risks and benefits of the treatment regimen.

• A major role of the nurse is to assist the patient and family to understand the treatment options and to cope with the uncertainties of treatment outcomes.

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Health education• About the signs and symptoms that indicate

infection.

• Whenever they experience a symptom that is not typical for them, they should contact their health care provider.

• About any prophylactic medication regimen, including dosage, indications, times, actions, and side effects.

• Avoid others with infections and crowds.

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Health education cont…• The patient and family also need to learn about

other ways to prevent infection.

• Instructed to monitor for subtle changes in physical status and must be informed of the importance of seeking immediate health care if changes occur.

• About the importance of continuing the treatment regimen and assisted in incorporating it into their lives.

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References

1. Wilson KJW, Waugh A. Ross and Wilson Anatomy and physiology in Health and illness. Eigth edition. NewYork; Churchill Livingstone:1998.

2. Smeltzer SC, Bare B. Textbook of Medical surgical Nursing. 10th edition. Philadelphia; Lippincott Williams and wilkins: 2004.

3. Guyton AC, Hall JE. Textbook of Medical Physiology. Eleventh edition. Philadelphia; Saunder (Elsevier) : 2006.