Immunology 4: Lymphoid Cells Study Notes

Immunology 4: Lymphoid Cells Overview

  • Instructor: Dr. Rao Dukkipati, Associate Professor, Rowan University, Shreiber School of Veterinary Medicine.

  • Contact: dukkipativ@rowan.edu

Study Resources

  • Lecture PowerPoints

  • Tizard, G. (2025). Veterinary Immunology, Eleventh Edition: Chapters 14, 15, 16 & 19.

  • Punt, J.A., et al. (2019). Kuby Immunology, Eighth Edition: Chapter 2. (Electronic copy available via Rowan Library: https://ebookcentral.proquest.com/lib/rowan/detail.action?docID=31360771)

Learning Objectives

  • Describe the structure of a typical lymphocyte.

  • Describe major lymphocyte populations, including their origin, distribution, and location in the body.

  • Illustrate the important surface molecules typically expressed by T and B lymphocytes.

  • Describe the structure of a T Cell Receptor (TCR) and the genes encoding the variable antigen binding regions of the TCR.

  • Describe the structure of a B Cell Receptor (BCR).

Cells of the Immune System

  • Covered in Lectures 3-5.

  • Lecture 3 & 4 focus on foundational concepts, while Lecture 5 summarizes the topic.

Adaptive Immune Responses

Summary Diagram

  • T helper (CD4+) cells are classified into two types:

    • T helper 1 (Th1) cells produce pro-inflammatory cytokines such as interferon-gamma (IFN-γ), interleukin (IL)-2, and tumor necrosis factor (TNF)-beta.

    • T helper 2 (Th2) cells produce cytokines IL-4, IL-5, IL-10, and IL-13.

  • Antigen presentation promotes different immune responses:

    • Presentation to Th1 cells promotes cell-mediated immunity (CMI).

    • Presentation to Th2 cells promotes antibody production (humoral immunity).

  • CMI responses are predominant with intracellular organism infections.

  • Humoral responses are predominant with extracellular organism infections.

  • Importance of T- and B-cells in adaptive immunity.

Role of Lymphocytes in Adaptive Immune Response

  • Lymphocytes and their role in adaptive immunity illustrated through the following components:

    • Antigen Processing Cell

    • Helper T Cell

    • Effector Cells (includes T and B Cells)

Types of Lymphocytes

  • Three main types develop from the common lymphoid progenitor:

    • B Lymphocytes

    • T Lymphocytes

    • NKT Cells (a subset resembling Natural Killer cells)

    • Natural Killer (NK) Cells

  • Lymphocytes visually appear similar but carry distinct sets of cluster of differentiation (CD) molecules on their surface.

Visual Examples of Lymphocytes

  • Images included to demonstrate various types of lymphocytes including T Cell and B Cell Receptors.

  • Scanning electron micrographs showcase lymphocytes in animals (e.g., horse, cat, dog).

Distribution of Lymphocytes in the Body

  • Blood: 2%

  • Spleen: 13%

  • Intestine: 10%

  • Bone Marrow: 10%

  • Lymph Nodes: 40%

  • Other tissues: 25%

Development of T and B Lymphocytes

  • Sites of development noted:

    • Cytotoxic T cells in Peyer's patches (for ruminants).

    • Bone marrow in birds.

  • Naïve helper (Th) cells can differentiate into various helper cell subsets (e.g., Th1, Th2, Th17) based on polarizing cytokines produced by antigen-presenting cells.

  • Natural killer (NK) cells discussed in Lecture 7.

T Cell Development: Positive and Negative Selection in the Thymus

  • Negative Selection: Elimination of self-reactive T cells.

  • Positive Selection: Stimulation of remaining, non-self-reactive T cells.

Differentiating Lymphocytes

  • Identifying cluster of differentiation (CD) molecules on lymphocyte surfaces aids in differentiation.

  • Phenotype detection achieved through fluorescent-labeled antibodies and flow cytometry.

B Cell Receptors (BCR)

  • Structure:

    • Composed of an immunoglobulin (IgM or IgD) and signal transduction molecule (CD79).

    • BCR binds to free antigens (Ag).

    • Contains MHC class II molecules for antigen presentation to T helper cells.

    • Fc receptors for immunoglobulins and complement receptors enhance regulation and feedback.

B Cell Receptors: Their Ligands and Functions

  • B cells act as antigen-presenting cells during secondary responses by processing and presenting peptides via MHC class II molecules to helper T-cells.

Structure of Complete B Cell Receptor (BCR)

  • BCR is an immunoglobulin molecule (IgD or IgM) and includes CD79 for signal transduction.

  • Detailed structure covered in Lectures 15 & 16.

T Cell Receptors (TCR)

  • Structure:

    • T cells express TCR associated with glycoproteins CD4 (in helper T cells) and CD8 (in cytotoxic T cells).

    • TCR binds only to antigen presented on MHC molecules, not free antigens.

TCR Ligands and Functions

  • TCRs are crucial for recognizing antigens presented by MHC molecules.

  • Self-reactive TCRs are generally destroyed during fetal development to prevent autoimmunity.

T Cell Receptors: Alpha/Beta vs. Gamma/Delta

  • TCR types include:

    • α/β TCR (90-99% of cells in humans and mice).

    • γ/δ TCR (specific to gut and skin, and a larger proportion in ruminants' blood).

  • Classical Th and Tc cells are of the α/β type, while γ/δ T cells engage in both innate and adaptive responses and can recognize antigens without MHC.

TCR Genes

  • Antigen binding regions have genes similar to those of immunoglobulin (Ig) with segments V, D, and J.

  • These segments are rearranged during T cell development to generate diversity in TCR, crucial for recognizing different antigens.

Importance of TCR in Autoimmunity

  • TCR recognition of self antigens may culminate in autoimmunity through mutations.

  • Examples include rheumatoid arthritis and multiple sclerosis.

  • Potential treatment includes monoclonal antibodies targeting defective TCRs.