Chapter 2: Cells and Tissues of the Immune System The Cells: Most cellular responses occur in the lymphatic tissue, or connective tissue, even though most of the cells discussed below are found in the blood circulation. Neutrophils - most common circulating leukocyte - phagocyte - segmented nucleus - granulocyte: specific granules - azurophilic granules - - first responder Eosinophils - granulocyte - bilobed, sausage shaped nucleus - red/orange granules - locations: Basophils - granulocyte - S-shaped nucleus obscured by granules - similar in function to mast cells - contain granules that stain dark purple/blue - IgE receptors Mast Cells - derived from the bone marrow - location: - membrane-bound granules - IgE receptors Abbas, Lichtman and Pillai8_Figure 2-1A; p.14 Abbas, Lichtman and Pillai8_Figure 2-1D; p.14 Abbas, Lichtman and Pillai8_Figure 2-1C; p.14 Abbas, Lichtman and Pillai8_Figure 2-1B; p.14Monocytes (aka. Mononuclear phagocytes) - largest leukocyte; differentiates into macrophages (tissue) - phagocytic function; APC - different lineages (see figure 2-2 below) - innate and adaptive immunity roles - kidney-shaped or horseshoe-shaped nucleus - tissue repair Abbas, Lichtman and Pillai8_Figure 2-3A; p.15 Abbas, Lichtman and Pillai8_Figure 2-2; p.15Antigen Presenting Cells - A cell capable of capturing and presenting antigens to another cell - Examples: Dendritic cells – long, membranous projections - myeloid lineage - recognize molecules on pathogens Lymphocytes - adaptive immune cell - round, slightly indented nucleus, very little cytoplasm - each clone expresses a single antigen receptor - B cells - T cells Abbas, Lichtman and Pillai8_Figure 2-5; p.20 Abbas, Lichtman and Pillai8_Figure 2-7A; p.23Naive, Effector, and Memory Lymphocytes Naive lymphocytes – Effector Lymphocytes – - plasma cell – antibody producing cell; a differentiated B cell - extensive Golgi - eccentric nucleus with a characteristic clock-shaped face Effector T cells - helper T cells - cytotoxic T cells Abbas, Lichtman and Pillai8_Figure 2-8A; p.23 Abbas, Lichtman and Pillai8_Table 2-3, p. 22Memory lymphocytes – We will discuss these different types of lymphocytes in greater detail later in the semester. Innate Lymphoid Cells Natural Killer (NK) cells –Abbas, Lichtman and Pillai8_Figure 2-6; p.21The Tissues: primary (aka. generative or central) lymphoid tissues secondary (aka. peripheral) lymphoid tissues Bone Marrow Abbas, Lichtman and Pillai8_Figure 2-9; p.25Thymus - bilobed organ located at the anterior mediastinum - lobules - septa - cortex - medulla - T cell maturation - travel from the bone marrow; leave and enter circulation (naive, mature) Clinical correlation: DiGeorge Syndrome Abbas, Lichtman and Pillai8_Figure 2-10A, B; p.27Lymphatic System Components: Circulation: Lymph Node - ~500 lymph nodes - outer fibrous capsule - outer cortical region - inner medullary region Abbas, Lichtman and Pillai8_Figure 2-11; p.28 Abbas, Lichtman and Pillai8_Figure 2-12B; p.29Antigen can enter the lymph nodes by one of two ways: Note the cortex, paracortex, and medulla - B cells and T cells self assemble into their regions using chemokines Abbas, Lichtman and Pillai8_Figure 2-12A; p.29Spleen - secondary lymphoid organ - function: - organization Clinical importance: Individuals who do not have their spleen, have a greater risk of infection with certain types of bacteria such as those that encapsulated (pneumococci and meningococci). Abbas, Lichtman and Pillai8_Figure 2-15 A,B;
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