ligand for a receptor on its own surface. The result of this upregulation
and ligand-receptor binding is an increase in T cell proliferation. T
cell–derived cytokines such as tumor necrosis factor-alpha and -beta
(TNF-αandβ) induce leukocyte recruitment. Production of gamma-(γ)-
interferon (γ-IFN) by helper T cells attracts and activates macrophages
(monocytes comprise most of the cellular infiltrate). γ-IFN also converts
other cells (such as endothelial cells) to antigen-presenting cells by induc-
tion of class II MHC expression, which further augments the response.
The result of the activity of helper T cells is a dramatic increase in the
number of lymphocytes and macrophages at the test site, which produces
swelling. IL-1 is synthesized by antigen-presenting cells and macrophages
with helper T cells as the targets.
- The answer is d.(Alberts, pp 1396–1400. Abbas, pp 58–59, 91–92, 148.
Kindt, pp 448–454.)There are some viruses in which antibody-mediated
immunity is critical to prevention/recovery, whereas with others cell-medi-
atedimmunity is the key. Therefore, both memory T and memory B cells
will be formed. B cells will divide to form a plasma cell and a memory B
cell. Activated T cells enlarge to form large lymphocytes and subsequently
undergo cell proliferation to form T cells and memory T cells. In these
responses, macrophages phagocytose virus (answer a).Cells that become
infected with virus can be killed by CD8+cytotoxic T cells (answers c and e),
which can react to the antigen in the presence of MHC class I molecules.
T and B cell areas of the spleen and lymph nodes will be involved in the
filtration of blood and lymph, respectively. B cell differentiation requires
the presence of CD4+helper T cells and an antigen-presenting cell (APC).
The APC will phagocytose the virus and present it to helper T cells in the
presence of MHC class II molecules (answer b).The B cell also presents
antigen during viral infections.
180.The answer is d.(Alberts, pp 1372–1374. Junqueira, p 274. Ross and
Pawlina, pp 410, 412.)Passage of lymphocytes from the lymphoid compart-
ment of the lymph node to the bloodstream involves passage from the effer-
ent lymphatic vessel to the thoracic duct and eventually into the venous
system (at the juncture of the left brachiocephalic and subclavian veins).
The region of the lymph node marked with the asterisk in the photomicro-
graph is the hilus of the lymph node. Passage from the blood to the lym-
phoid compartment involves specific homing receptors on lymphocytes,
286 Anatomy, Histology, and Cell Biology