Immuno T cells

Speaker: Dr. Rawah Faraj, DVM, MSc., Ph.D., Assistant Professor of Immunology
Course: VMED 809A Immunology, Spring 2026
Topics Covered: T cell activation, cell-mediated immunity, antigen processing and presentation.

Thymus Gland: Location for T-lymphocyte maturation and education.
Bursa of Fabricius: Location for B-lymphocyte maturation.
Bone Marrow: Initial maturation and education for both T and B lymphocytes.
Process of Maturation:
- In the bone marrow, immature T cells undergo mitosis.
- In the thymus, each T cell matures by producing T cell receptors.
- Each mature T cell has a unique T cell receptor and can differentiate into either:
- T helper cells: assist other cells in the immune response.
- Cytotoxic T cells: directly kill infected or cancerous cells.

Mature T Cells:
- Circulate throughout the body and are categorized into types based on function.
- Each T cell expresses a unique T cell receptor (TCR).

Definition: The process where white blood cells such as macrophages, neutrophils, and dendritic cells engulf and digest foreign particles or pathogens.

Definition: Signaling proteins released by immune cells that regulate and modulate the immune response.
Etymology: Derived from Greek words "cyto" (cell) and "kinos" (movement).
Examples include interleukins, interferons, and tumor necrosis factors.

Role: Activate B cells and cytotoxic T cells; crucial coordinator in immune responses.

Function: Recognize and kill infected cells by identifying antigens on the surface of those cells.
Activation Steps:
1. Antigen Recognition: Detects foreign antigen using MHC-I molecules and T-cell receptors (TCR).
2. Clonal Selection: Proliferation of activated cytotoxic T cells.
3. Lethal Hit: Target cell (infected or cancerous) undergoes apoptosis.

Definition: A group of molecules displayed on cell surfaces that aid in the immune system's ability to recognize foreign molecules.
Types:
- MHC Class I: Present on all nucleated cells, presenting endogenous antigens to CD8+ T cells.
- MHC Class II: Present primarily on antigen-presenting cells (APCs) like macrophages and dendritic cells, presenting exogenous antigens to CD4+ T helper cells.

Definition: Essential white blood cells in the adaptive immune response characterized by their T-cell receptors (TCRs).
Subtypes:
- T helper cells: Aid in the activation of B cells and other immune functions.
- Cytotoxic or killer T cells: Directly destroy intracellular pathogens.
TCR Function: Recognizes small peptide fragments of antigens presented by MHC molecules on infected cells.

Structure: Composed of two polypeptide chains forming a binding site for antigenic peptides.
Types:
- α/β T Cells: Majority of T cells with alpha and beta chains.
- γ/δ T Cells: Minor population with gamma and delta chains.
TCR/CD3 Complex: Associated with additional polypeptide chains (CD3 complex) including γ, δ, ε chains, and a ζ (zeta) chain.

Definition: An immune response that does not involve antibodies but involves the activation of phagocytes, antigen-specific cytotoxic T lymphocytes, and helper T lymphocytes.
Mechanism: Involves the release of various cytokines in response to antigens.
Examples: Immunofluorescence image showing cytotoxic T cells killing a cancer cell via lytic granules.

Types of APCs: Includes dendritic cells, macrophages, and B cells.
Function:
- Dendritic cells uptake virus antigens, upload bacterial antigens.
- Macrophages engulf and process antigens and present them to T cells.
- B cells bind microbial toxins using receptors for further immune response activation.

Role: Specialized cells that detect, phagocytize, and destroy bacteria and harmful organisms; also present antigens to T cells.
Cytokines Released: Includes IL-1, IL-6, and tumor necrosis factor alpha, which initiate inflammation.
Origin: Derive from blood monocytes that differentiate in tissues, circulating throughout the body.
Types and Functions:
- Alveolar Macrophage: Located in lung alveoli; initiates immune responses to respiratory pathogens.
- Kupffer Cells: Located in the liver; involved in immune response and tissue remodeling.
- Microglia: In the CNS; help in the elimination of dead neurons and controlling brain immunity.

Toll-Like Receptors (TLRs): Recognize different pathogen components (e.g., sugars, LPS) to initiate immune responses.
Interaction with Pathogens: Binding of bacteria to macrophage receptors leads to the release of cytokines, initiating phagocytosis and digestion of pathogens.

Process: T cells do not recognize free antigens but must see them associated with MHC molecules.
- T helper (TH) cells recognize processed antigens displayed by MHC class II molecules.
- Cytotoxic T cells recognize endogenously synthesized antigens presented by MHC class I molecules.

Definition: CD proteins are integral for immune function, aiding in cell activation, adhesion, and response regulation.
Current Identified CD Proteins: Ranges from CD1 to CD371, used in research in immunology and cancer therapy.
Key CD Markers:
- CD4: Present on T helper cells, assists in binding MHC class II.
- CD8: Found on cytotoxic T cells, assists in binding MHC class I.

Examples Include:
- CD3: Found on T cells (both Human and Mouse).
- CD4, CD8: Key markers for T lymphocyte identification.
- More extensive lists include markers for other immune cell types (e.g., B cells, NK cells, Stem cells).

MHC Class I:
- Presents endogenous antigens from intracellular pathogens;
- Found on all nucleated cells.
MHC Class II:
- Presents exogenous antigens processed by APCs to CD4+ T cells.

Binding: Cytotoxic T cell binds to infected cell using TCR and MHC class I.
Perforin Release: Creates pores in the infected cell's membrane.
Target Cell Destruction: Enzymes enter and induce apoptosis in the infected cell.

Which cell type primarily attacks and kills cancer cells?
- A. red blood cell B. cytotoxic T cell C. platelet D. mast cell
How are antigens presented to naïve T cells?
- A. Antigen-antibody complexes bound to a B cell; B. Infectious organisms release lipopolysaccharide; C. Macrophages display peptides with MHC molecules; D. Neutrophils release antigens from phagosomes; E. NK cells lyse infected cells.
What T cell surface marker is present on T helper cells?
- A. CD4; B. CD8; C. CD10; D. CD20; E. CD28.
List the Antigen-Presenting Cells.
Describe the functions of macrophage cells based on their location.
What is the function of nitric oxide?