Adaptive Immunity Overview

Introduction

• Focus on adaptive immunity and lymph nodes.
• Previous discussions on inflammatory response.

Antigen Presentation in Lymph Nodes

• Macrophages and neutrophils carry antigens on MHC 2 molecules.
• Germinal centers in lymph nodes contain B cells.
• B cell receptors (BCR) are typically IgD antibodies.

B Cell Activation

• BCRs undergo recombination to vary binding domains for different antigens.
• Antigens bind to BCRs, activating naive B cells.
• Activated B cells then undergo receptor-mediated endocytosis.
• Chromosome 6 produces MHC 2 for antigen presentation.

T Helper Cell Activation

• Macrophages present antigens to naive T helper cells using MHC 2.
• T helper cells have TCRs and CD4 proteins.
• Activation requires primary signal (MHC 2 interaction) and co-stimulation (B7 and CD28 interaction).
• Interleukin 1 is released for further signaling.

T Helper Cell Differentiation

• T helper cells can differentiate into Th1 or Th2 cells.
• Th2 cells are crucial for producing interleukins IL-4 and IL-5.
• IL-2 and IL-4 stimulate T cell proliferation.

B Cell Proliferation and Differentiation

• IL-4 causes clonal expansion of B cells.
• IL-5 induces differentiation into plasma and memory B cells.
• Plasma cells produce antibodies specific to antigens.

Antibody Functions

• Antibodies neutralize, precipitate, lyse, agglutinate, or opsonize antigens.
• Connects adaptive and innate immunity through processes like opsonization.

Humoral Immunity

• Triggered by free antigens and involves B cells and antibodies.
• Involves cytokines IL-4, IL-5, and IL-6 from T helper cells.

Cell-Mediated Immunity

• Focuses on intracellular threats (e.g., viral or cancerous cells).
• Cytotoxic T cells recognize MHC 1 and foreign peptides.
• Induces apoptosis through perforins and granzymes.

Natural Killer Cells

• Part of innate immunity, not adaptive.
• Kill via absence of MHC 1, presence of Ma molecules, or IgG recognition.
• Mechanism similar to cytotoxic T cells with perforins and granzymes.

Summary

• Humoral immunity deals with external antigens through B cells.
• Cell-mediated immunity deals with internal cell threats through cytotoxic T cells.
• Natural killer cells, though similar, are part of innate immunity.