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CELLS AND TISSUES OF THE IMMUNE SYSTEM

There are two main types of adaptive immunity—cell-mediated (or cellular) immunity, which is responsible for defense against intracellular microbes, and humoral immunity, which

protects against extracellular microbes and their toxins ( Fig. 6-2 ). Cellular immunity is mediated by T (thymus-derived) lymphocytes, and humoral immunity is mediated by B (bone

marrow-derived) lymphocytes and their secreted products,

Figure 6-2Humoral and cell-mediated immunity.

Figure 6-3Histology of a lymph node. A, The organization of the lymph node, with an outer cortex containing follicles and an inner medulla. B, The location of B cells (stained green,

using the immunofluorescence technique) and T cells (stained red) in a lymph node. C, A germinal center.

Figure 6-4The T-cell receptor (TCR) complex. A, Schematic illustration of TCRa and TCRb chains linked to the CD3 complex. B, Recognition of MHC-associated peptide displayed on

an antigen-presenting cell (top) by the TCR. Note that the TCR-associated z chains and CD3 complex deliver signals (signal 1) upon antigen recognition, and CD28 delivers signals (signal

2) upon recognition of costimulators (B7 molecules).

Figure 6-5Structure of antibodies and the B-cell antigen receptor. A, The B-cell receptor complex composed of membrane IgM (or IgD, not shown) and the associated signaling proteins

Iga and Igb. CD21 is a receptor for a complement component that also promotes B-cell activation. B, Crystal structure of a secreted IgG molecule, showing the arrangement of the variable

(V) and constant (C) regions of the heavy (H) and light (L) chains. (Courtesy of Dr. Alex McPherson, University of California, Irvine, CA.)

Figure 6-6The morphology and functions of dendritic cells (DC). A, The morphology of cultured dendritic cells. (Courtesy of Dr. Y-J. Liu, M. D. Anderson Cancer Center, Houston.) B,

The location of dendritic cells (Langerhans cells) in the epidermis. (Courtesy of Dr. Y-J. Liu, M. D. Anderson Cancer Center, Houston.) C, The role of dendritic cells in capturing microbial

antigens from epithelia and transporting them to regional lymph nodes.

Figure 6-7 A highly activated natural killer cell with abundant cytoplasmic granules. (Courtesy of Dr. Noelle Williams, Department of Pathology, University of Texas Southwestern

Medical School, Dallas, TX.)

Figure 6-8Schematic representation of NK-cell receptors and killing. NK cells express activating and inhibitory receptors; some examples of each are indicated. Normal cells are not

killed because inhibitory signals from normal MHC class I molecules override activating signals. In tumor cells or virus-infected cells, there is increased expression of ligands for

activating receptors, and reduced expression or alteration of MHC molecules, which interrupts the inhibitory signals, allowing activation of NK cells and lysis of target cells. KIR, killer

cell Ig-like recepors.

 

Figure 6-9The HLA complex and the structure of HLA molecules. A, The location of genes in the HLA complex is shown. The sizes and distances between genes are not to scale. B,



Schematic diagrams and crystal structures of class I and class II HLA molecules. (Crystal structures are courtesy of Dr. P. Bjorkman, California Institute of Technology, Pasadena, CA.)

Figure 6-10Antigen processing and recognition. The sequence of events in the processing of a cytoplasmic protein antigen and its display by class I MHC molecules are shown at the top.

The recognition of this MHC-displayed peptide by a CD8+ T cell is shown at the bottom.

 

TABLE 6-1-- Association of HLA with Disease


Date: 2016-04-22; view: 697


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