9.3.5 Disorders of Immune System

Some conditions that stimulate a defective immune response or destroy immune system are called disorders of immune system. These include allergies, autoimmune diseases, and transplant rejections.

Definition

Disorders of Immune System: Some conditions that stimulate a defective immune response or destroy immune system are called disorders of immune system.

Main Idea

• Some conditions stimulate a defective immune response.
• Some conditions destroy the immune system.
• These are called disorders of immune system.
• Main disorders include:

Core Concept

• Disorders of immune system = defective immune response or destruction of immune system
• Allergies = defective immune responses to allergens
• Autoimmune diseases = immune system attacks healthy cells
• Transplant rejections = immune system attacks transplanted tissue
• Allergy mechanism = IgE antibodies; histamine release
• Autoimmune examples = anaemias, diabetes, vitiligo
• Transplant rejection = T cells and B cells involved
• Immunosuppressive drugs = prevent rejection

Detailed Explanation

Disorders of Immune System

Some conditions that stimulate a defective immune response or destroy immune system are called disorders of immune system.

Allergies

• Allergies are defective immune responses leading to chronic health conditions like Hay fever, eczema, asthma and food allergy.
• The immune system of allergy patients overreacts when allergens (like pollen, dust or mold) are inhaled or ingested or enter through skin.
• The body starts producing large quantity of special antibodies IgE (Immunoglobulin E).
• This IgE binds with basophils to release inflammatory chemicals like histamine.
• Histamine increases capillary leakiness, swelling, mucus secretion, inflammation and other allergic responses.
• Antihistamine drugs block some of the effects of histamine, relieving the symptoms of allergies.
• Vaccination can be effective treatment of allergy specially for asthma.

Autoimmune Disease

• In autoimmune disease, the immune system attacks the healthy cells of body's organs and tissues by mistake.
• The antibodies are produced against body's own components and begin to destroy them.
• There are more than 80 types of autoimmune diseases.
• They can affect almost any part of your body.
• For example:
• Unfortunately, at present there is no way to cure autoimmune diseases.
• The autoimmune response can be suppressed with drugs.

Transplant Rejections

• It is occasionally desirable to transplant some tissue or an organ such as the skin, kidney, heart, or liver, from one person to another to replace a non-functional damaged or lost body part.
• In such cases, there is a danger that the recipient cells may recognize the donor's organ or tissue as being foreign.
• This triggers the recipient's immune mechanisms, which may act to destroy the donor tissue.
• Such a response is called transplant rejection.

Role of T Cells in Transplant Rejection

• Although the mechanism of rejection probably varies with the nature of the tissue and the degree of incompatibility, all the mechanisms require that the host helper T cells come into contact with the graft tissue's major histocompatibility complex (MHC) antigens.
• This contact is probably mediated by the dendritic cells of the graft tissue itself.
• At this point, three different possibilities exist.
• In the first, antigen-specific TH cells stimulate the activation and proliferation of appropriate T cells, which then enhance a focused attack on the transplant tissue.
• In the second, responsive antigen-specific TH cells move to the graft site, where they release lymphocytes.
• These recruit monocyte/macrophages and T cells to the graft site and maintain them at the scene while they destroy the tissue.
• Lymphokines are signaling molecules released by immune cells (like lymphocytes) that help communicate with other immune cells to fight infections. They act like messengers, coordinating the immune response to eliminate pathogens.

Role of B Cells in Transplant Rejection

• There is a third mechanism in which antibodies plays a role.
• The responsive helper T cell interacts with the appropriate B cell clone, producing a shower of antibodies to the implanted tissue's MHC antigens.
• These can trigger either complement-mediated graft damage or facilitating the phagocytosis of the grafted tissue by macrophages.

Science, Technology and Society Connections

Explain why a transplant recipient is given immune suppressant drugs and determine what implications does this has on his life.

• Organ transplantation has become a routine procedure due to improvement of surgical techniques, better tissue typing and the availability of drugs that more selectively inhibit rejection of transplanted tissues and prevent the patient from becoming immunologically compromised.
• Transplant rejection occurs as a delayed hypersensitivity reaction as a function of lymphocytes and not due to antibodies.
• Administration of immunosuppressive drugs enhances tolerance.
• People receiving immunosuppressive drugs have side effects like pain, diarrhoea, leukopenia, sepsis, lymphoma, thrombocytopenia, skin rashes, anaphylactic reaction, hypertension, hyperkalemia and neurotoxicity (tremors, seizures, hallucination).
• Hence, each system is affected, so the person starts to feel weakness and gets fatigue easily.

Summary Table of Disorders of Immune System

Summary of Allergy Mechanism

Summary of Transplant Rejection

Intermediate Level

Disorders of Immune System

Allergy Mechanism

Autoimmune Diseases

Transplant Rejection

Formula / Mathematical Form

Not applicable to this topic.

Solved Example

Not applicable to this topic (descriptive topic).

Important Points

• 1. Disorders of immune system are conditions that stimulate defective immune response.
• 2. Allergies are defective immune responses.
• 3. Allergies lead to chronic health conditions.
• 4. Examples: hay fever, eczema, asthma, food allergy.
• 5. Allergens are inhaled, ingested, or enter through skin.
• 6. Body produces large quantity of IgE antibodies.
• 7. IgE binds with basophils.
• 8. Histamine is released.
• 9. Histamine increases capillary leakiness, swelling, mucus secretion, inflammation.
• 10. Antihistamine drugs block histamine effects.
• 11. Vaccination can be effective for allergy.
• 12. Autoimmune disease: immune system attacks healthy cells.
• 13. Antibodies are produced against body's own components.
• 14. More than 80 types of autoimmune diseases.
• 15. Examples: anaemias, diabetes, vitiligo.
• 16. No cure for autoimmune diseases.
• 17. Autoimmune response can be suppressed with drugs.
• 18. Transplant rejection: recipient immune system attacks donor tissue.
• 19. T cells and B cells are involved in transplant rejection.
• 20. Immunosuppressive drugs are used to prevent rejection.

Remember

• - Disorders of immune system = defective immune response or destruction of immune system
• - Allergies = defective immune responses to allergens
• - Autoimmune diseases = immune system attacks healthy cells
• - Transplant rejections = immune system attacks transplanted tissue
• - Allergy mechanism = IgE antibodies; histamine release
• - Autoimmune examples = anaemias, diabetes, vitiligo
• - Transplant rejection = T cells and B cells involved
• - Immunosuppressive drugs = prevent rejection

Common Mistakes

• 1. Confusing allergies and autoimmune diseases — Allergies = response to allergens; autoimmune = attack on own cells.
• 2. Mixing up the mediators — IgE and histamine for allergies; T cells and B cells for transplant rejection.
• 3. Forgetting the role of IgE — Produced in allergies.
• 4. Mixing up the examples — Hay fever, eczema, asthma = allergies; anaemias, diabetes, vitiligo = autoimmune.
• 5. Believing autoimmune diseases are curable — Currently no cure.
• 6. Forgetting the role of immunosuppressive drugs — Prevent transplant rejection.
• 7. Mixing up the side effects — Pain, diarrhoea, leukopenia, sepsis, etc.
• 8. Thinking transplant rejection is only antibody-mediated — T cells are also involved.
• 9. Forgetting the role of MHC — Recognized as foreign in transplant rejection.
• 10. Mixing up the types of hypersensitivity — Allergies are immediate; transplant rejection is delayed.

Quick Revision

Some conditions that stimulate a defective immune response or destroy immune system are called disorders of immune system. Allergies are defective immune responses leading to chronic health conditions like Hay fever, eczema, asthma and food allergy. The immune system of allergy patients overreacts when allergens (like pollen, dust or mold) are inhaled or ingested or enter through skin. The body starts producing large quantity of special antibodies IgE (Immunoglobulin E). This IgE binds with basophils to release inflammatory chemicals like histamine. Histamine increases capillary leakiness, swelling, mucus secretion, inflammation and other allergic responses. Antihistamine drugs block some of the effects of histamine, relieving the symptoms of allergies. Vaccination can be effective treatment of allergy specially for asthma. In autoimmune disease, the immune system attacks the healthy cells of body's organs and tissues by mistake. The antibodies are produced against body's own components and begin to destroy them. There are more than 80 types of autoimmune diseases. They can affect almost any part of your body. For example: Some types of anaemias are caused by antibodies that destroy a person's red blood cells. Many cases of insulin-dependent (juvenile-onset) diabetes occur because the insulin-secreting cells of the pancreas are the victims of a misdirected immune response. Vitiligo is a chronic autoimmune disorder that causes patches of skin to lose pigment or colour. Unfortunately, at present there is no way to cure autoimmune diseases. The autoimmune response can be suppressed with drugs. It is occasionally desirable to transplant some tissue or an organ such as the skin, kidney, heart, or liver, from one person to another to replace a non-functional damaged or lost body part. In such cases, there is a danger that the recipient cells may recognize the donor's organ or tissue as being foreign. This triggers the recipient's immune mechanisms, which may act to destroy the donor tissue. Such a response is called transplant rejection. Although the mechanism of rejection probably varies with the nature of the tissue and the degree of incompatibility, all the mechanisms require that the host helper T cells come into contact with the graft tissue's major histocompatibility complex (MHC) antigens. This contact is probably mediated by the dendritic cells of the graft tissue itself. At this point, three different possibilities exist. In the first, antigen-specific TH cells stimulate the activation and proliferation of appropriate T cells, which then enhance a focused attack on the transplant tissue. In the second, responsive antigen-specific TH cells move to the graft site, where they release lymphocytes. These recruit monocyte/macrophages and T cells to the graft site and maintain them at the scene while they destroy the tissue. Lymphokines are signaling molecules released by immune cells (like lymphocytes) that help communicate with other immune cells to fight infections. They act like messengers, coordinating the immune response to eliminate pathogens. There is a third mechanism in which antibodies plays a role. The responsive helper T cell interacts with the appropriate B cell clone, producing a shower of antibodies to the implanted tissue's MHC antigens. These can trigger either complement-mediated graft damage or facilitating the phagocytosis of the grafted tissue by macrophages. Organ transplantation has become a routine procedure due to improvement of surgical techniques, better tissue typing and the availability of drugs that more selectively inhibit rejection of transplanted tissues and prevent the patient from becoming immunologically compromised. Transplant rejection occurs as a delayed hypersensitivity reaction as a function of lymphocytes and not due to antibodies. Administration of immunosuppressive drugs enhances tolerance. People receiving immunosuppressive drugs have side effects like pain, diarrhoea, leukopenia, sepsis, lymphoma, thrombocytopenia, skin rashes, anaphylactic reaction, hypertension, hyperkalemia and neurotoxicity (tremors, seizures, hallucination). Hence, each system is affected, so the person starts to feel weakness and gets fatigue easily.

60-Second Revision

• Disorders of immune system = defective immune response or destruction of immune system
• Allergies = defective immune responses to allergens
• Autoimmune diseases = immune system attacks healthy cells
• Transplant rejections = immune system attacks transplanted tissue
• Allergy mechanism = IgE antibodies; histamine release
• Autoimmune examples = anaemias, diabetes, vitiligo
• Transplant rejection = T cells and B cells involved
• Immunosuppressive drugs = prevent rejection
• Warning: Allergies involve IgE and histamine; transplant rejection involves T cells and B cells

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