Immunology Quiz: Antibodies and Hypersensitivity

Immunology Week 4

• The course is titled "Immunology", Week 4, taught by Hanzely, DMSc, PA-C, RD.
• The course is within the "Where Dreams Find Direction" program at South College.
• The institution is South College, founded in 1882.

Instructional Objectives

• Inventory antigens and antibodies/immunoglobulins (IgA, IgD, IgE, IgG, and IgM)
• Illustrate the immune response (cell-mediated and humoral immunity)
• Inspect the 4 types of hypersensitivity
• Compare autoimmune and immunodeficiency diseases
• Define HIV, transmission, and diagnostic/monitoring testing
• Compare major blood group systems (ABO and Rh) and other systems
• Contrast anti-Rh antibody formation and hemolytic disease of the newborn (HDN)
• Differentiate Type and Cross Match, Type and Screen, Direct and Indirect Coombs tests
• Inventory indications for blood transfusions (red cells, cryoprecipitate, platelets, fresh-frozen plasma) and review transfusion reactions.

Refresh Immunity

• Immunity is separated into innate and adaptive.
• Innate immunity involves nonspecific physical/physiological barriers (skin, GI lining, gastric acid) and phagocytes (neutrophils and macrophages).
• Adaptive immunity involves specific targets (acquired immunity).
  • Cell-mediated immunity involves T-lymphocytes (CD8+ and CD4+ T cells).
  • Antibody-mediated (humoral) immunity involves B-lymphocytes and secreted antibodies.

Immune Response (Simplified)

• Local neutrophils encounter pathogens, initiating phagocytosis and triggering cytokines.
• Cytokines induce local vasodilation and attract more neutrophils and monocytes.
• Monocytes differentiate into macrophages.
• Macrophages and neutrophils continue phagocytosis.
• Macrophages act as antigen-presenting cells (APCs), presenting antigens to T-cells (cytotoxic T cells, helper T cells, and regulatory T cells).
• B-cells become activated, and some mature into memory B-cells, while others become plasma B-cells that secrete antibodies (immunoglobulins).

Immunoglobulins

• Immunoglobulins (Ig), including IgA, IgD, IgE, IgG, and IgM, act as antibodies.
• Immunoglobulins are measured in mg/dL.

Immunoglobulin Details

• Immunoglobulins are used synonymously with antibodies.
• Reference ranges vary by age and measurement method.
• Serum immunoglobulin testing can indicate disease but isn't diagnostic.
• Electrophoresis is sometimes needed to separate them.
• They come in five isotypes: IgG, IgA, IgM, IgE, IgD.
• Antibodies vary in how they bind to antigens and whether they cross the placenta.

Monoclonal vs. Polyclonal

• Polyclonal antibodies bind to different epitopes of the same antigen.
• Monoclonal antibodies bind to one epitope of the antigen.

IgG

• IgG constitutes approximately 75% of serum immunoglobulins.
• It's the major circulating antibody and crosses the placenta.
• It plays a role in neutralization, opsonization, complement activation, and antibody-dependent cytotoxicity.
• Various disorders (rheumatologic, pulmonary, renal, immune diseases) can increase IgG levels.
• IgG deficiency may lead to frequent or more severe infections.

IgA

• IgA accounts for approximately 15% of immunoglobulins.
• It's present in tears, blood, respiratory and GI secretions.
• It protects mucosal tissues and maintains homeostasis with microbiota.
• Increased levels are seen in several anti-inflammatory disorders. Decreased levels can be seen in certain diseases like leukemia and IgA deficiency.

IgM

• Primarily responsible for ABO blood grouping.
• Responds immediately during an infection.
• Involved in many infection responses.
• Forms a pentamer structure with 10 antigen-binding sites.
• Effectively forms antigen-antibody complexes and activates the complement system.
• Does not cross the placenta. A high IgM level in a newborn indicates possible infection in utero.

IgE

• Mediates responses to allergies and parasitic diseases.
• Used to detect allergic disorders and hypersensitivity.
• Not useful as a standalone test.
• Not significant in bacterial defenses.
• Does not activate the complement system.
• Increased in various diseases.

IgD

• Not well understood and rarely evaluated.
• Might be involved in B-cell function and immune responses.

Hypersensitivity

• An exaggerated immune response, potentially ranging from uncomfortable to fatal.
• Classified into 4 types in the Gell and Coombs system.
  • Type I hypersensitivity is IgE-mediated, leading to allergies.
  • Type II hypersensitivity is antibody-mediated, often leading to autoimmune reactions.
  • Type III hypersensitivity involves immune complexes depositing in vessels and joints, leading inflammation.
  • Type IV hypersensitivity is cell-mediated, often manifesting in delayed reactions (takes days to develop).

HIV

• HIV, a virus, causes progressive immune system failure, increasing the risk of infections and cancers.
• CD4 ("cluster of differentiation 4") proteins on T cells are important markers in HIV and help cytotoxic T cells.
• Measuring the viral load and CD4 count helps in measuring HIV progression and tailoring treatment approaches.
• Certain blood tests, like ELISA and CBC, help in diagnosis of HIV. The tests look for antibodies to HIV and/or presence of infection in the blood.

Blood Types

• Blood types are determined by antigens on red blood cells.
• ABO blood types are A, B, AB, and O.
• Antigens trigger immune responses.
• Type A blood has anti-B antibodies; Type B blood has anti-A antibodies; Type AB has neither and Type O has both.
• Incompatible blood transfusions can lead to reactions.

Rh Factor

• Rh factor is an erythrocyte antigen first discovered in rhesus monkeys.
• Antibodies to Rh factor usually do not occur naturally but develop after exposure and can be a cause for issues in transfusions.
• Testing and cross-matching are essential for determining compatibility before a transfusion, especially in extreme cases.

Transfusion Reactions

• Transfusion reactions result from exposure to incompatible blood.
• Two antigen-antibody reactions occur, leading to clumping and hemolysis of red blood cells.

Hemolytic Disease of the Newborn

• A condition where maternal antibodies attack fetal red blood cells.
• This can cause severe effects including jaundice and anemia.

Coombs Tests

• Coombs tests check for antibodies against red blood cells (RBCs).
  • Direct Coombs test: checks for antibodies attached directly to the RBC surface.
  • Indirect Coombs test: checks for unbound antibodies in the serum.

Type and Screen/Cross

• Determines ABO and Rh typing.
• Additional antibodies are included in the testing process.
• Includes type and screen and an indirect Coombs test.
• Ordered if there is a high likelihood of transfusion.
• Usually done in cases where blood transfusion is imminent or very likely.

Blood Product Indications

• Whole blood (not as efficient), packed red blood cells, platelet-rich plasma (PRP) for patients with low platelet counts, and fresh frozen plasma for patients with clotting factor deficiencies are all common blood products.
• Different methods and considerations are involved in obtaining these blood products.