Immune Disorders Power Hour Flashcards

Lines of Defense: The immune system is organized into two primary categories that cooperate to protect the body.
- Innate Immunity: This is the body's first line of protection. It is characterized as being non-specific, meaning it does not target specific antigens but rather provides a general response to foreign invaders. Components include:
  - Granulocytes: Specialized white blood cells with secretory granules.
  - Macrophages: Large phagocytic cells found in stationary form in the tissues.
  - Neutrophils: The most abundant type of granulocytes.
  - Natural Killer (NK) Cells: Cytotoxic lymphocytes that respond to virally infected cells and tumor formation.
  - Dendritic Cells: Professional antigen-presenting cells (APCs) that act as a bridge between the innate and adaptive systems.
- Adaptive Immunity: This system provides specialized defense and long-term memory. It is characterized by specificity to certain antigens. The primary players are:
  - B cells: Responsible for antibody-mediated immunity.
  - T cells: Responsible for cell-mediated immunity.

Granulocytes vs. Agranulocytes: White blood cells (leukocytes) are categorized based on the presence of microscopic granules in their cytoplasm.
- Granulocytes: Remembered by the acronym "NEB."
  - Neutrophils: Primary responders to bacterial infection.
  - Eosinophils: Involved in allergic reactions and parasitic infections.
  - Basophils: Release histamine during inflammatory and allergic reactions.
- Agranulocytes: Lack visible granules in the cytoplasm.
  - Monocytes: These cells circulate in the blood.
  - Macrophages: These are the mature form of monocytes that have migrated into tissues to perform phagocytosis.
Agranulocytosis: This refers to an acute condition involving a severe and dangerous reduction in the count of white blood cells (especially neutrophils), whereas its presence or absence dictates the body's ability to fight off infection.

Lymphoid Lineage: It is critical to understand the evolution of cell types from hematopoietic stem cells into specialized immune effectors. This lineage primarily produces NK cells, T cells, and B cells.
Roles and Activation of Lymphocytes:
- T-cells: These cells activate once a pathogen's antigen is "presented" to them by an antigen-presenting cell (APC) using MHC molecules.
- B-cells: These cells have a multi-step activation process:
  1. Encountering a foreign pathogen/antigen directly.
  2. Creating specific antibodies to match that pathogen.
  3. Receiving communication/signals from T-cells to refine the response.
Gene Rearrangement: This is a broad process occurring in B and T cells that allows for massive diversity in the receptors they express. Through genetic shuffling, the immune system can recognize an almost infinite number of unique pathogens.
Marginal Zone B Cells: These are specialized B cells located in the marginal zone of the spleen. They play a pivotal role in the early response to blood-borne pathogens, particularly encapsulated bacteria.

Neutrophils: These are essential for immune protection as the first responders to infection, using phagocytosis and the release of enzymes to destroy invaders.
Eosinophils: Crucial for defending against multicellular parasites and modulating inflammatory responses, particularly in asthma and allergies.
Basophils: Contribute to immune defense by releasing heparin (an anticoagulant) and histamine (which increases blood flow to tissues), essential for the inflammatory response.

The Complement System: A part of the immune system that "complements" the ability of antibodies and phagocytic cells to clear microbes and damaged cells. It provides protection through:
- Opsonization: Marking pathogens for destruction.
- Chemotaxis: Attracting immune cells to the site.
- Cell Lysis: Directly rupturing the cell membranes of pathogens.
Chronic Inflammation: In conditions of chronic inflammation, the body’s inflammatory response does not shut off, leading to tissue damage.
- Rheumatoid Arthritis (RA): An autoimmune disorder where inflammation is generated by specific signals and cytokines (such as TNF-alpha and interleukins) that cause the immune system to attack the synovial joints.

MHC Overview: The MHC is a set of surface proteins essential for the adaptive immune system to recognize foreign molecules. It allows the body to distinguish "self" from "non-self."
MHC Pairings:
- $MHC\,I$ : Found on nearly all nucleated cells; it pairs with $CD8$ cytotoxic T-cells.
- $MHC\,II$ : Found on professional antigen-presenting cells (dendritic cells, macrophages, B cells); it pairs with $CD4$ helper T-cells.

Mechanisms of Pathogen Neutralization: There are three primary ways an antibody stops a pathogen from causing harm:
1. Neutralization: Blocking the part of the pathogen that causes infection or allows it to enter a cell.
2. Opsonization: Tagging the pathogen so it is more easily recognized and eaten by phagocytes.
3. Complement Activation: Triggering the complement system to destroy the pathogen through the Membrane Attack Complex (MAC).
The Five Types of Antibodies (Immunoglobulins):
- IgG: The most abundant antibody; provides long-term immunity and can cross the placenta.
- IgA: Found in mucosal areas (saliva, tears, breast milk) to protect body openings.
- IgM: The first antibody produced during an initial immune response; indicates recent infection.
- IgE: Associated with allergic reactions and defense against parasitic worms.
- IgD: Found on the surface of B cells; primarily functions as an antigen receptor.

Hypersensitivity Reactions: There are four distinct types:
- Type I: Immediate hypersensitivity (e.g., allergies, anaphylaxis).
- Type II: Cytotoxic reactions (e.g., blood transfusion reactions).
- Type III: Immune complex-mediated (e.g., Lupus, glomerulonephritis).
- Type IV: Delayed-type hypersensitivity (e.g., contact dermatitis, TB skin test).
Autoimmunity: This occurs when the immune system loses "self-tolerance" and begins to attack the body's own healthy cells and tissues. This failure in discrimination leads to various autoimmune diseases.
Immunodeficiency Disorders: There are two general types:
1. Primary Immunodeficiency: Inherited genetic defects in the immune system.
2. Secondary Immunodeficiency: Acquired due to external factors like infection (HIV), chemotherapy, or malnutrition.
Key Conditions:
- Severe Combined Immunodeficiency (SCID): A severe genetic disorder characterized by the complete absence or lack of function of T-cells and B-cells ("Bubble Boy disease").
- Common Variable Immunodeficiency (CVID): An immune disorder characterized by low levels of serum immunoglobulins (antibodies) and an increased susceptibility to infections.