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 granulocyte bilobed sausage shaped nucleus red orange granules locations Abbas Lichtman and Pillai8 Figure 2 1A p 14 Eosinophils Abbas Lichtman and Pillai8 Figure 2 1D p 14 Basophils granulocyte S shaped nucleus obscured by granules similar in function to mast cells contain granules that stain dark purple blue IgE receptors Abbas Lichtman and Pillai8 Figure 2 1C p 14 Mast Cells Abbas Lichtman and Pillai8 Figure 2 1B p 14 derived from the bone marrow location membrane bound granules IgE receptors Monocytes 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 15 Antigen 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 Abbas Lichtman and Pillai8 Figure 2 7A p 23 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 Naive Effector and Memory Lymphocytes Abbas Lichtman and Pillai8 Table 2 3 p 22 Naive lymphocytes Effector Lymphocytes plasma cell antibody producing cell a differentiated B cell extensive Golgi eccentric nucleus with a characteristic clock shaped face Abbas Lichtman and Pillai8 Figure 2 8A p 23 Effector T cells helper T cells cytotoxic T cells Abbas Lichtman and Pillai8 Figure 2 6 p 21 Memory lymphocytes We will discuss these different types of lymphocytes in greater detail later in the semester Innate Lymphoid Cells Natural Killer NK cells The Tissues primary aka generative or central lymphoid tissues secondary aka peripheral lymphoid tissues Bone Marrow Abbas Lichtman and Pillai8 Figure 2 9 p 25 Thymus bilobed organ located at the anterior mediastinum Abbas Lichtman and Pillai8 Figure 2 10A B p 27 lobules septa cortex medulla T cell maturation Clinical correlation DiGeorge Syndrome travel from the bone marrow leave and enter circulation naive mature Lymphatic System Abbas Lichtman and Pillai8 Figure 2 11 p 28 Abbas Lichtman and Pillai8 Figure 2 12B p 29 Components Circulation Lymph Node 500 lymph nodes outer fibrous capsule outer cortical region inner medullary region Antigen 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 29 Spleen secondary lymphoid organ function organization Abbas Lichtman and Pillai8 Figure 2 15 A B p 32 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