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Hipersensibilidade Tipo II - Mediada por anticorpo
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Hipersensibilidade Tipo II - Mediada por anticorpo

Introduction and Return to YouTube

The speaker introduces themselves as Roni Brito, a teacher of immunology, and explains that they have been on a break from recording videos for the YouTube channel due to vacation and university activities. They express their intention to resume creating educational content for students in the field of immunology.

Returning to Recording Videos

  • After a break, the speaker decided it was time to start recording videos again.
  • They plan to cover hypersensitivity types 2 and 3 in upcoming videos.
  • Despite being busy with experiments and university work, they will make an effort to release new content regularly.

Understanding Hypersensitivity Reactions

The speaker provides an overview of hypersensitivity reactions before delving into type 2 hypersensitivity.

Definition of Hypersensitivity

  • Hypersensitivity is an exaggerated immune response against harmless antigens.
  • It involves a coordinated reaction by the immune system's components.
  • Unlike normal immune responses, hypersensitivity reactions can cause damage without pathogenic antigens.

Examples of Type 2 Hypersensitivity

The speaker discusses examples of type 2 hypersensitivity reactions caused by excessive immune responses against harmless antigens.

Examples of Type 2 Hypersensitivity

  • Some individuals may have strong reactions to normally harmless antigens like pollen or commensal bacteria.
  • These exaggerated immune responses can lead to conditions such as allergic rhinitis or inflammatory bowel disease.
  • Autoimmune diseases are also considered type 2 hypersensitivities since the immune system targets self-antigens.

Immune Response Against Self-Antigens

The speaker explains the concept of immune responses against self-antigens and the development of autoimmune diseases.

Immune Response to Self-Antigens

  • In some cases, the immune system mounts a response against self-antigens, leading to autoimmune diseases.
  • Removing self-antigens from our bodies is not possible, so the immune system's reaction can cause harm.
  • Persistent microorganisms or environmental antigens can also trigger excessive immune responses.

Type 2 Hypersensitivity and Tissue Damage

The speaker discusses how type 2 hypersensitivity reactions can lead to tissue damage in certain conditions.

Examples of Tissue Damage

  • Infections like tuberculosis or paracoccidioidomycosis can cause inflammation and tissue damage due to persistent microorganisms.
  • Allergies to environmental antigens such as dust mites or pollen can result in uncontrolled immune responses and tissue damage.

Introduction to Hypersensitivity

In this section, the instructor introduces the concept of hypersensitivity and discusses the difficulty in eliminating immune responses. They also mention the different types of hypersensitivity and their mechanisms.

Types of Hypersensitivity

  • Type 1 hypersensitivity, also known as immediate hypersensitivity, is mediated by IgE antibodies and mast cells.
  • Type 2 hypersensitivity involves antibodies binding to cell surface or extracellular matrix antigens, leading to opsonization and phagocytosis.
  • Type 3 hypersensitivity is mediated by immune complexes formed by antigen-antibody binding, which can cause inflammation when deposited in certain tissues.
  • Type 4 hypersensitivity is mediated by T lymphocytes and involves inflammation, destruction of target cells, and granuloma formation.

Mechanism of Type 2 Hypersensitivity

This section focuses on type 2 hypersensitivity, which is caused by antibodies targeting self or tissue antigens. The mechanism involves opsonization and phagocytosis.

Antibody Binding and Opsonization

  • Antibodies (IgG/IgM) bind to self or tissue antigens.
  • Neutrophils and macrophages possess receptors for the constant region (Fc) of antibodies.
  • When neutrophils/macrophages bind to antibody Fc region, they release granules containing lysosomal enzymes.
  • Lysosomal enzymes can cause tissue damage due to reactive oxygen species production.

Conclusion

New Section

This section discusses the phenomenon of opsonization and phagocytosis, as well as inflammation mediated by complement and FC receptors.

Opsonization and Phagocytosis

  • Auto-antibodies bind to specific regions on red blood cells (RBCs).
  • Neutrophils bind to the Fc region of the auto-antibodies.
  • Phagocytosis of RBCs by neutrophils leads to a decrease in circulating RBCs.
  • Opsonization can also occur through the complement system, where IgG antibodies bind to antigens on RBCs.
  • Activation of the complement cascade leads to destruction of RBCs.

Inflammation Mediated by Complement and FC Receptors

  • Auto-antibodies bind to tissues, leading to the recruitment of neutrophils.
  • Neutrophils release their contents, causing inflammation in capillaries.
  • Presence of complement proteins further enhances phagocytosis and inflammation.
  • These mechanisms contribute to diseases such as autoimmune hemolytic anemia and immune-mediated vasculitis.

New Section

This section explores diseases caused by autoantibodies that result in cell destruction without tissue damage or inflammation.

Abnormal Physiological Responses without Tissue Damage

  • Autoantibodies can bind to normal cellular receptors and alter their functions.
  • This can lead to abnormal physiological responses without causing tissue damage or inflammation.

New Section

This section discusses how autoantibodies can cause abnormal physiological responses without tissue damage using an example involving muscle contraction.

Example: Muscle Contraction

  • Normally, acetylcholine is released at nerve-muscle junctions, leading to muscle contraction.
  • In the presence of autoantibodies, these receptors can be affected, resulting in abnormal physiological responses without tissue damage.

New Section

This section summarizes the three main mechanisms discussed: opsonization and phagocytosis, inflammation mediated by complement and FC receptors, and abnormal physiological responses without tissue damage.

Recap of Mechanisms

  • Opsonization and phagocytosis involve the binding of autoantibodies to target cells, leading to their destruction by neutrophils.
  • Inflammation mediated by complement and FC receptors involves the recruitment of neutrophils and activation of complement proteins, causing tissue damage.
  • Abnormal physiological responses without tissue damage occur when autoantibodies bind to normal cellular receptors, altering their functions.

Autoantibodies and Myasthenia Gravis

This section discusses the role of autoantibodies in a disease called myasthenia gravis.

Autoantibodies and Acetylcholine Receptors

  • Autoantibodies can bind to acetylcholine receptors, leading to a condition called myasthenia gravis.

Effects of Autoantibody Binding

  • When acetylcholine is released by nerve endings, the binding of autoantibodies inhibits its interaction with the receptor, resulting in muscle weakness and fatigue.
  • This leads to symptoms such as double vision, difficulty speaking, chewing, and swallowing.

Autoantibodies and Graves' Disease

This section explains how autoantibodies contribute to Graves' disease.

Role of Autoantibodies in Graves' Disease

  • In Graves' disease, autoantibodies bind to TSH receptors on thyroid cells.
  • This constant stimulation of the receptors leads to excessive production of thyroid hormones.
  • Symptoms include enlarged thyroid gland (goiter), protruding eyes, menstrual irregularities, anxiety, rapid heartbeat, and weight loss.

Other Diseases Caused by Autoantibodies

This section provides examples of other diseases caused by autoantibodies.

Examples of Diseases Caused by Autoantibodies

  • Purpura thrombocytopenic autoimmune: Antibodies target platelet membrane proteins, leading to increased bleeding.
  • Pemphigus vulgaris: Antibodies disrupt intercellular junctions in skin cells, resulting in blister formation.
  • Acute rheumatic fever: Antibodies against streptococcus cell wall antigens cross-react with myocardial antigens, causing inflammation and potentially leading to myocarditis and arthritis.
  • Type 2 diabetes: Antibodies inhibit insulin receptor binding, leading to the development of diabetes mellitus.

Summary of Type 2 Hypersensitivity

This section summarizes the key points discussed about type 2 hypersensitivity.

Key Points

  • Type 2 hypersensitivity involves autoantibodies targeting cellular or matrix antigens, leading to diseases affecting specific cells or tissues.
  • Mechanisms include phagocytosis, complement-mediated inflammation, and abnormal physiological responses without tissue damage.
Video description

HIPERSENSIBILIDADE DO TIPO II Os distúrbios causados por respostas imunes são chamados de hipersensibilidade. Este termo surgiu da definição clínica de imunidade como uma sensibilidade, baseando-se na observação de que um indivíduo que tenha sido exposto a um antígeno exibe uma reação detectável, ou torna-se sensível, a encontros subsequentes com esse antígeno. Em geral, as respostas imunes erradicam os organismos infectantes sem provocar graves lesões aos tecidos do hospedeiro. No entanto, essas respostas são, algumas vezes, controladas de maneira inadequada, inapropriadamente direcionadas aos tecidos do hospedeiro ou desencadeadas por microrganismos comensais ou antígenos ambientais, os quais geralmente são inofensivos. Nestas situações, a resposta imune, normalmente benéfica, torna-se a causa da doença. Doenças mediadas por anticorpos são produzidas por anticorpos que se ligam a antígenos em determinadas células ou em tecidos extracelulares ou, ainda, por complexos antígeno-anticorpo que se formam na circulação e são depositados nas paredes dos vasos. Os anticorpos IgG e IgM podem causar lesão tecidual por meio da ativação do sistema complemento, recrutando células inflamatórias e interferindo nas funções celulares normais. Alguns desses anticorpos são específicos para antígenos de determinadas células ou da matriz extracelular e são encontrados ligados a essas células ou tecidos ou como anticorpos livres na circulação; as doenças induzidas por esses anticorpos são chamadas de hipersensibilidade do tipo II. Aulas relacionadas: Anticorpos: https://www.youtube.com/watch?v=Q26mP6CbPxU&t=33s Sistema Complemento: https://www.youtube.com/watch?v=rvLT7Ysd3mA&t=3046s Hipersensibilidade tipo I (Alergias): https://www.youtube.com/watch?v=tEKn47UvHIc&t=1324s Bibliografia: Imunologia Celular e Molecular, Capítulo 19: Reações de Hipersensibilidade| Abul K. Abbas, MBBS, Andrew H. Lichtman, MD, PHD and Shiv Pillai, MBBS, PHD.