a&p immune notes

Overview of Immune Cells and Antigen Presentation

T-helper Cells and Macrophages

  • MHC Class II Cells:

    • Function as the first immune cell encountered by antigens.

    • Macrophages capture and process antigens that do not belong in the body.

      • They utilize lysosomes containing acidic proteolytic enzymes.

    • After processing, they present antigen fragments on their membrane (Antigen Presentation).

The Role of T-helper Cells (CD4)

  • Antigen presentation activates T-helper (CD4) cells.

  • T-helper cells latch onto antigens to recognize them as foreign.

  • Once activated, T-helper cells signal B and other T cells to respond.

MHC Class I Presentation

  • Only nucleated cells can present antigens via MHC Class I.

  • Quality Control:

    • Cells check fragments off ribosomes to ensure the correct peptides are synthesized.

    • These peptides are displayed on the cell surface for immune cell inspection.

    • CD8 Cytotoxic T cells play a role in quality control by binding to MHC Class I molecules.

    • If a cell is malfunctioning, CD8 T cells remain attached.

Cytotoxic T Cells (CD8)

  • Perforins:

    • Cytotoxic T-cells release perforins to create pores in infected cells.

    • Function similarly to the Membrane Attack Complex in the complement cascade.

  • Cell Lysis and Necrosis:

    • The punctured holes allow for the injection of granzymes into the target cell, triggering apoptosis.

    • All cytotoxic cells have death receptors that can be used to induce cell death.

    • Cytotoxic T cells wait for chemical signals from the infected cell before killing it to determine if the cell can be saved.

The Role of T-helper Cells

  • T-helper cells activate B cells and enhance T cell response.

  • Primarily, T-cell responses are mediated through MHC Class I presentation, but T-helper cells can assist in this process.

Immunodeficiency and Autoimmunity

  • Immunodeficiencies:

    • Primary Immunodeficiency:

      • Examples include leukemia, where ineffective WBCs take over tissues.

    • Secondary Immunodeficiency:

      • A deficiency caused by external factors such as malnutrition.

  • Autoimmunity:

    • Refers to the breakdown of self-tolerance where the body mistakenly attacks its own cells.

  • Hypersensitivity:

    • An exaggerated immune response to typically harmless substances.

Specific Conditions

  • Autoimmune Diabetes:

    • Diagnosed typically over the age of 30 related to Type I diabetes.

  • Allergies:

    • The immune system overreacts, leading to severe allergic responses.

    • The “Hygiene Hypothesis” suggests that reduced exposure early in life leads to a higher prevalence of allergies through an imbalance between T-helper cell types.

Antibodies and Immunoglobins

  • The body produces five main types of immunoglobulins (Ig):

    • IgM: Indicates a recent infection if found in blood.

    • IgA: Found in breast milk and saliva, protecting neonates' gastrointestinal tracts.