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Lecture 3

MICR 270 Lecture 3: MICRO 270 Module 3 NOTES

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Queen's University
Microbiology and Immunology
MICR 270

MICRO 270 MODULE 3 The Immune Response: Adaptive Immune Response: 1. Antigen recognition via antigen-presenting cells (APC) a. Naïve T cells recognize invading antigens through the cell surface b. Presenting cells via MHC proteins 2. Lymphocyte activation a. Activated B and T cells divide rapidly b. B cells mature into plasma cells i. Production of antibodies c. Helper T cells secrete macrophages and other phagocytic cells to eliminate invading agents d. Cytotoxic T cells kill virus infected areas 3. Antigen elimination a. B cell antibodies and active T cells eliminate antigens 4. Apoptosis a. Once antigens are eliminated, activation of lymphocytes occurs and immune system response declines b. Apoptosis = programmed cell death 5. Memory a. Antigen specific immune cells remain in the body as memory cells b. Creates faster immune response to same antigen if it occurs again Antigen Presenting Cells and Antigen Recognition: • Antigen presenting cells (APCs) are used to take up foreign antigens o Example: Dendritic cells • Two categories of presenting cells • Professional APC’s: o Dendritic cells o Macrophages o B cells ▪ Use of phagocytosis or receptor-mediated endocytosis ▪ Use of MHC proteins on surface to display foreign antigen • Non-professional APC’s: o Fibroblast o Thymic and Thyroid epithelial cells o Glial cells o Pancreatic beta cells ▪ Does not constantly express MHC proteins ▪ Stimulation by certain cytokines • APC’s allow cytotoxic T cells to recognize protein MHC complex o Initiates immune response Two main receptors for antigen recognition: • B-cell receptors: o Antigen-specific antibody (BCR) and is membrane-bound or soluble. o Immunoglobulin molecule that is found on surface of B cells o Recognition of free antigens and antigens with MHC molecules o B-cells are one type of professional APC’s • T-cell receptors: o Membrane-bound antigen-specific receptor (TCR) found on the surface of T-cells o Cannot recognize antigens in free form ▪ MHC molecule must be present on the surface of APC • Specificity is found in MHC-antigen complex o Two types of co
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