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Biology in Human Welfare

Human Health and Disease: Cells of Acquired Immunity

• Acquired immunity is the immune response that our body develops after exposure to pathogens
• B lymphocytes (B cells) and T lymphocytes (T cells) are the key cells of acquired immunity
• These cells are derived from stem cells in the bone marrow

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B Lymphocytes (B cells)

• B cells are responsible for antibody-mediated immunity
• They mature in the bone marrow
• B cell receptors (BCRs) on their surface recognize specific antigens
• When activated, B cells differentiate into plasma cells that produce antibodies

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T Lymphocytes (T cells)

• T cells are responsible for cell-mediated immunity
• They mature in the thymus gland
• T cell receptors (TCRs) on their surface recognize specific antigens presented by antigen-presenting cells (APCs)
• There are different types of T cells, including helper T cells, cytotoxic T cells, and regulatory T cells

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Antigen-Presenting Cells (APCs)

• APCs present antigens to T cells to activate immune responses
• Dendritic cells, macrophages, and B cells are examples of APCs
• APCs engulf pathogens, process them, and present their antigens on major histocompatibility complex (MHC) molecules

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Helper T Cells

• Helper T cells (Th cells) play a crucial role in coordinating immune responses
• They recognize antigens presented by APCs through their TCRs
• Th cells secrete cytokines that activate other immune cells and stimulate B cells to produce antibodies

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Cytotoxic T Cells

• Cytotoxic T cells (Tc cells) are responsible for killing infected cells
• They recognize antigens presented by infected cells through their TCRs
• Tc cells release cytotoxic molecules (e.g., perforin, granzymes) to induce apoptosis in the infected cells

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Regulatory T Cells

• Regulatory T cells (Treg cells) help maintain immune tolerance and prevent excessive immune responses
• They suppress the activity of other immune cells, including B cells and T cells
• Treg cells play a role in preventing autoimmune diseases

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Antibodies (Immunoglobulins)

• Antibodies are glycoprotein molecules produced by plasma cells derived from B cells
• They have specific binding sites (paratopes) that recognize and bind to specific antigens (epitopes)
• Antibodies can neutralize pathogens, facilitate phagocytosis, activate complement system, and stimulate other immune cells

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Major Histocompatibility Complex (MHC)

• MHC molecules are cell surface proteins that present antigens to T cells
• MHC class I molecules present intracellular antigens to cytotoxic T cells
• MHC class II molecules present extracellular antigens to helper T cells

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Summary

• Acquired immunity involves B lymphocytes (B cells) and T lymphocytes (T cells)
• B cells are responsible for antibody-mediated immunity, while T cells are responsible for cell-mediated immunity
• Antigen-presenting cells (APCs) present antigens to T cells to activate immune responses
• Helper T cells (Th cells) coordinate immune responses, cytotoxic T cells (Tc cells) kill infected cells, and regulatory T cells (Treg cells) maintain immune tolerance
• Antibodies (immunoglobulins) produced by B cells bind to specific antigens and can neutralize pathogens or stimulate other immune cells Slide 11 ======

B Cell Activation and Antibody Production

• B cell activation occurs when the B cell’s BCR recognizes and binds to an antigen
• This binding stimulates the B cell to proliferate and differentiate into plasma cells
• Plasma cells produce and secrete antibodies specific to the antigen that activated them
• Antibodies can bind to antigens, neutralize them, and mark them for destruction by other immune cells

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T Cell Activation and Immune Response

• T cell activation requires the interaction of TCRs with antigens presented by APCs
• Helper T cells recognize antigens presented on MHC class II molecules and release cytokines to activate immune responses
• Cytotoxic T cells recognize antigens presented on MHC class I molecules and kill infected cells
• This coordinated response helps eliminate pathogens and infected cells

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Memory Cells and Secondary Immune Response

• After an initial immune response, some B and T cells differentiate into memory cells
• Memory cells have a longer lifespan and can quickly respond to the same antigen upon re-exposure
• During a secondary immune response, memory cells proliferate and differentiate into effector cells faster and with greater efficiency
• This leads to a quicker and stronger immune response

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Antibody Structure and Functions

• Antibodies are composed of four polypeptide chains: two heavy chains and two light chains
• The variable regions of the heavy and light chains form the antigen-binding site
• Antibodies can bind to antigens in various ways:
  • Neutralization: Preventing the antigen from entering host cells
  • Opsonization: Promoting phagocytosis by coating the antigen
  • Agglutination: Clumping pathogens together for easier elimination
  • Activation of complement system: Promoting inflammation and lysis of cells

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Primary and Secondary Immune Disorders

• Primary immune disorders result from genetic defects affecting the development or function of immune cells
• Examples include severe combined immunodeficiency (SCID) and agammaglobulinemia
• Secondary immune disorders are acquired due to factors such as infections, medications, or autoimmune diseases
• HIV/AIDS is an example of a secondary immune disorder

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Vaccines and Immunization

• Vaccines are preparations that stimulate the immune system to produce an immune response to specific antigens
• They contain attenuated or inactivated pathogens, their components, or synthetic antigens
• Vaccination helps prevent diseases by providing immunity without the risk of severe illness
• Common vaccines include those against measles, polio, influenza, and hepatitis

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Monoclonal Antibodies

• Monoclonal antibodies (mAbs) are antibodies derived from a single clone of B cells
• They are produced in laboratory settings and can be specific to a particular antigen
• mAbs have various applications, including targeted therapy for cancer, autoimmune diseases, and diagnostic tests
• Examples of therapeutic mAbs include trastuzumab, rituximab, and infliximab

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Autoimmune Diseases

• Autoimmune diseases occur when the immune system mistakenly attacks and damages its own cells and tissues
• Examples include rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, and type 1 diabetes
• Autoimmune diseases can involve various mechanisms, such as autoantibody production or activation of autoreactive T cells
• Treatment typically focuses on suppressing immune responses and alleviating symptoms

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Immunotherapy

• Immunotherapy is a type of cancer treatment that uses the body’s immune system to fight cancer cells
• Approaches include immune checkpoint inhibitors, adoptive cell transfer, and immune stimulants
• These therapies can enhance the ability of the immune system to recognize and eliminate cancer cells
• Immunotherapy has shown promising results in treating various types of cancer

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Conclusion

• B cells and T cells are essential cells of acquired immunity
• They recognize antigens and activate immune responses to protect against pathogens
• Antibodies produced by B cells play a crucial role in antibody-mediated immunity
• The immune system can be affected by genetic disorders, infections, autoimmune diseases, and cancer
• Vaccines, monoclonal antibodies, and immunotherapy are important tools in combating diseases and improving human health

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Disorders of the Immune System

• Allergies:

  • Allergies occur when the immune system overreacts to harmless substances (allergens) such as pollen, dust mites, or certain foods.
  • Symptoms can include sneezing, itching, watery eyes, and difficulty breathing.
  • Common allergic conditions include hay fever, asthma, and eczema.

• Autoimmune Diseases:

  • Autoimmune diseases occur when the immune system mistakenly attacks healthy cells and tissues in the body.
  • Examples include rheumatoid arthritis, systemic lupus erythematosus, and multiple sclerosis.
  • These diseases can cause chronic inflammation and damage to various organs and systems.

• Immunodeficiency Disorders:

  • Immunodeficiency disorders are a group of disorders in which the immune system is weakened or non-functioning.
  • Primary immunodeficiency disorders are usually genetic and present from birth, while secondary immunodeficiency disorders can be acquired later in life.
  • Examples include severe combined immunodeficiency (SCID), HIV/AIDS, and certain types of cancers.

• Hypersensitivity Reactions:

  • Hypersensitivity reactions occur when the immune system overreacts and causes damage to the body’s own tissues.
  • There are four types of hypersensitivity reactions: type I (immediate hypersensitivity), type II (cytotoxic hypersensitivity), type III (immune complex-mediated hypersensitivity), and type IV (delayed hypersensitivity).

• Transplant Rejections:

  • Transplant rejections occur when the recipient’s immune system recognizes the transplanted organ or tissue as foreign and attacks it.
  • This can happen due to differences in human leukocyte antigen (HLA) types between the donor and recipient.
  • Medications called immunosuppressants are used to prevent transplant rejections.

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Applications of Immunology

• Diagnosis of Diseases:

  • Immunological techniques are used in diagnosing various diseases, including infectious diseases and autoimmune disorders.
  • Examples include enzyme-linked immunosorbent assay (ELISA), Western blotting, and immunofluorescence.

• Development of Vaccines:

  • Immunology plays a vital role in the development of vaccines that protect against infectious diseases.
  • Vaccines stimulate the immune system to produce an immune response, leading to immunity against specific pathogens.

• Genetic Engineering:

  • Immunology is essential in genetic engineering techniques, such as recombinant DNA technology and gene therapy.
  • These techniques allow the production of therapeutic proteins and modification of genes for medical purposes.

• Cancer Immunotherapy:

  • Immunotherapy is a promising approach for treating cancer by harnessing the power of the immune system.
  • Techniques include immune checkpoint inhibitors, adoptive cell transfer, and cancer vaccines.

• Prevention of Organ Transplant Rejections:

  • The field of immunology has contributed to the development of immunosuppressant drugs and techniques to minimize the risk of rejection after organ transplantation.

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Summary: Cells of Acquired Immunity

• Acquired immunity involves B lymphocytes (B cells) and T lymphocytes (T cells) that develop from stem cells.
• B cells mediate antibody-mediated immunity, while T cells mediate cell-mediated immunity.
• Helper T cells (Th cells) coordinate immune responses, cytotoxic T cells (Tc cells) kill infected cells, and regulatory T cells (Treg cells) maintain immune tolerance.
• Antibodies produced by plasma cells derived from B cells can neutralize pathogens, promote phagocytosis, agglutinate pathogens, and activate the complement system.
• Immunological disorders, such as allergies, autoimmune diseases, and immunodeficiency disorders, occur when the immune system malfunctions.
• The field of immunology has various applications, including disease diagnosis, vaccine development, genetic engineering, cancer immunotherapy, and prevention of organ transplant rejections.

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Equations

• Antibody Structure Equation:

  • Antibodies = 2 Heavy chains (H) + 2 Light chains (L) + 2 Antigen-binding sites (Variable regions)

• Cell-Mediated Immunity Equation:

  • Infected cell + Tc cell recognition of antigen-MHC complex → Cytotoxic response (perforin, granzymes) → Apoptosis of infected cell

• Antibody-Mediated Immunity Equation:

  • Antigen + B cell recognition of antigen → B cell activation → Plasma cell differentiation → Antibody production

• Immunodeficiency Equation:

  • Weakened immune system + Increased susceptibility to infections = Immunodeficiency disorder

• Autoimmune Equation:

  • Self-antigens + Autoantibodies or autoreactive T cells = Autoimmune disease

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Example: Antigen Presentation

• Dendritic cells are an example of antigen-presenting cells (APCs).
• When a pathogen enters the body, dendritic cells engulf and process it.
• The processed antigens are presented on MHC class II molecules on the dendritic cell’s surface.
• Helper T cells recognize these antigens and become activated, initiating an immune response.

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Example: Antibody Functions

• Neutralization Example:

  • Antibodies can neutralize the toxins produced by bacteria, preventing them from causing harm.

• Opsonization Example:

  • Antibodies can coat bacteria, facilitating their recognition and phagocytosis by macrophages.

• Agglutination Example:

  • Antibodies can bind to multiple pathogens (e.g., bacteria) and clump them together, making it easier for phagocytes to eliminate them.

• Complement Activation Example:

  • Antibodies can activate the complement system, leading to the recruitment of immune cells and lysis of target cells.

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Example: Vaccination

• Influenza Vaccine Example:
  • The influenza vaccine contains inactivated or attenuated strains of the influenza virus.
  • When the vaccine is administered, the immune system recognizes the antigens present in the vaccine.
  • B cells produce antibodies specific to the antigens, and memory cells are also generated.
  • Upon subsequent exposure to the influenza virus, the immune system mounts a faster and stronger immune response, preventing severe illness.

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Example: Monoclonal Antibodies

• Rituximab Example:
  • Rituximab is a monoclonal antibody used in the treatment of certain types of lymphomas and autoimmune diseases.
  • It targets a specific antigen, CD20, which is expressed on the surface of B cells.
  • By binding to CD20, rituximab triggers the destruction of B cells, contributing to the treatment of these conditions.

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Example: Autoimmune Disease

• Rheumatoid Arthritis Example:
  • Rheumatoid arthritis is an autoimmune disease characterized by inflammation in the joints.
  • The immune system mistakenly attacks the synovium, a protective membrane around the joints.
  • This leads to chronic inflammation, pain, swelling, and ultimately, joint damage.

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Example: Cancer Immunotherapy

• Immune Checkpoint Inhibitors Example:
  • Immune checkpoint inhibitors, such as pembrolizumab and nivolumab, are used in the treatment of various cancers.
  • They block proteins called immune checkpoints, which regulate immune responses.
  • By inhibiting these checkpoints, the drugs can enhance the immune system’s ability to recognize and destroy cancer cells.