Final exam is scheduled for April 17, from 8 to 10 AM in ISEC 102.
Students should avoid making plans to leave campus before the exam.
The confusing concepts question will remain open for 24 hours after activation to earn participation credit.
Lecture 17 Overview: The Immune System
Focus: Adaptive Immunity (Part 2)
T cells: Linking humoral and cell-mediated immunity
MHC molecules and antigen-presenting cells
Topics Covered:
HIV Virus and AIDS
Stages of HIV Infection:
Primary: Non-specific flu-like symptoms
Clinical latency: Decline in T helper (Th) cells
Early symptomatic disease: High fever, unusual infections, some cancers
AIDS: T cell count < 200 cells/µl, associated with unusual cancer and infections.
Clostridioides difficile (C. diff)
Non-member of the Enterobacteriaceae family, causes colitis and life-threatening CDI.
Risk is higher for patients on antibiotics.
Produces cytotoxins leading to pseudomembranous colitis.
Sepsis
Often caused by bacterial infections.
Characterized by SIRS symptoms:
Abnormal WBC count
Abnormal body temperature
Rapid heart/breathing rates
Considered a medical emergency.
Antigen-Presenting Cells (APCs)
Engulf microbes, digest, and present antigens for T cell activation.
MHC Class I: Present on all nucleated cells (absent in RBCs)
MHC Class II: Found on professional APCs (e.g., dendritic cells, macrophages, B cells).
T Cells: Types and Activation
Main Types of T Cells:
Cytotoxic T Cells (TC): CD8 receptors; kill infected host cells.
T Helper Cells (TH): CD4 receptors; help activate B cells and TC cells.
Activation Process:
T cells require antigen presentation by APCs via MHC molecules.
TCR (T-cell receptor) binds antigens within MHC molecules.
MHC Molecules and Antigen Processing
MHC Class I Presentation:
Present intracellular pathogens.
Antigens from degraded proteins in the cytoplasm.
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Pathogen proteins degraded
Antigens presented on MHC I on cell surface.
MHC Class II Presentation:
Present extracellular pathogens.
Pathogens phagocytosed and digested.
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Antigens loaded onto MHC II from the endosome for presentation.
T Cell Activation Process
Signals Required for Activation:
Antigen-MHC binding (TCR to MHC)
Second signal (CD28 on T-cell binds B7 on APC)
Cytokine signaling from TH cells.
Effects of Activation:
Clonal expansion of effector and memory TC cells.
Effector TC cells move to infection sites and destroy infected cells.
Case Study: Bare Lymphocyte Syndrome (BLS)
Symptoms: Frequent infections due to low IgG, IgA, and IgM levels.
Test results: Absence of MHC Class II proteins, affecting TH cell activation and antibody response.
Treatment: Bone marrow transplant recommended due to defective antigen presentation.
Summary of Innate vs. Adaptive Immunity
The adaptive immune response provides capability for stronger and faster responses upon re-encounter with pathogens and includes memory formation crucial for long-term immunity.