Lymphoid Tissue and Lymphatic Organs Defense Mechanisms

š Innate / Non-specific š Adaptive / Specific š Epithelial Barriers š Humoral Immune reaction (B cells) š Cell-mediated immune reaction (T cells) š Phagocytic cells š Pattern Recognition Receptors š Acute inflammation š Neutrophils, Macrophages, Mast cells, other granulocytes š NK cells š Antigen Presenting Cells (APCs) š Complement system Pattern Recognition Receptors

š Innate (non-specific) immune system š Recognize molecular patterns š Found on phagocytes

š Types š Endocytic PRRs

š Signaling PRRs š Toll-like receptors (TLRs) š CD 14 receptor š NOD receptor Natural Killer cells (NK cells) Adaptive / Specific Some Definitions

š Antigen š Self: Major Histocompatibility Complex (MHC) – I and II š Non-self: Foreign š Epitope š Antibody š IgG, IgM, IgD, IgE, IgA Adaptive Immune System: Cells

š B cells š Humoral immune response š B cells receptors: Immunoglobulins (antibodies) š T cells š T cytotoxic cell (CD8+) š Cell-mediated immune response š T helper cell (CD4+) š Active in initial phase of both types Antigen Presenting Cells (APCs)

š Professional

š Non Professional Lymphoid Tissue

š Reticular connective tissue š Network of reticular fibers š Network of stellate reticular cells š Fibroblasts, Macrophages, Dendritic cells š Very numerous lymphocytes Localization of Lymphoid Tissue

š Lymphatic Organs š Lymph node š Spleen š Thymus š Mucosa-Associated Lymphoid Tissue (MALT) š Tonsils š GALT š BALT (Bronchi-Associated LT) Types of Lymphoid Tissue

š Diffuse: B and T cells š Nodular (Follicular): Mainly B cells š Spherical aggregates of lymphoid tissue š Primary and secondary

š B cell selection š Follicular Dendritic cells š Th cells š Macrophages Lymph Node Spleen š White pulp š PALS (T cells) š Splenic (lymphoid) nodules (B cells)

š Red pulp š Splenic cords š Splenic Sinusoids š Pulpal veins

Primary follicle Thymus

š Epithelial origin š No reticular connective tissue š Only T cells š No lymphoid nodules š No immune reactions against non-self antigens š T cell school Thymus Thymus

š Autoimmunity š Involution