Page 514 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com mebooksfree.com CHAPTER 58 Cellular Basis of the Immune Response 503 mebooksfree.com
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Stem
Bone
cell
marrow

Thymus

CD4 – – – Double-negative
–
–
(CD4 , CD8 )
CD8
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mebooksfree.com mebooksfree.com Death of cells with TCRs CD4 + + + Positive selection involves mebooksfree.com mebooksfree.com
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cell; no TCR
TCR
Double-positive
+
+
(CD4 , CD8 )
CD8
cell; has TCR
TCR
the survival of cells with
that do not react with
TCRs that react with
self MHC proteins
self MHC proteins
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mebooksfree.com mebooksfree.com Negative selection involves CD4 + + + Survival of cells with mebooksfree.com mebooksfree.com
Dead
CD8
cell
TCR

TCRs that do not
the death of cells with TCRs
that recognize self antigens
recognize self antigens

Dead
CD8
cell CD4 + + + Differentiation of double-positive
TCR
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cell into a single-positive cell (either
+
+
CD4 or CD8 ) upon contact with
either class II or class I MHC protein,
respectively
–
CD4
CD4
+
CD8
CD8
+
TCR
TCR
FIGURE 58–2
Development of T cells. Note the positive and negative selection that occurs in the thymus. MHC, major histocompatibility
complex; TCR, T-cell receptor. by helper (CD4-positive) T cells, which produce interleukins
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mebooksfree.com mebooksfree.com mebooksfree.com (Table 58–3). For example, helper T cells make (1) interleu- mebooksfree.com
T CELLS
T cells perform several important functions, which can be
kin (IL)-2, which activates CD4 and CD8 cells; (2) IL-4,
divided into two main categories, namely, regulatory and
which help B cells make antibodies, especially IgE; and
effector. The regulatory functions are mediated primarily
(3) gamma interferon, which enhances killing by

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