Lymphoid System and Cellular Immunology Answers 281169.The answer is a.(Abbas, pp 188, 191. Kindt, pp 434–435.)Because of the
shortage of human organs for transplant, xenotransplantation is considered as
the main potential solution for obtaining donor organs. Xenotransplantation
induces hyperacute graft rejection since human preformed antibodies recog-
nize [alpha]Gal(1–3)[beta]Gal terminal carbohydrates present on animal
endothelial cells in the graft. Interestingly, Old World monkeys and humans
do not express that xenoantigen on their endothelial cells.
170.The answer is d.(Abbas, pp 81–82. Kindt, pp 40–41, 245–248. Alberts,
pp 1406–1409.)The organ in the photomicrograph is the thymus, which pro-
duces CD4+(helper) and CD8+(cytotoxic) T cells. It functions in the genera-
tion of self/nonself discrimination because self-reactive T cells are deleted
and self-MHC-restricted cells are expanded during their education within
the thymus. T cell receptors for antigen develop develop during the educa-
tion of T cells in the thymus. Those T cells also develop homing receptors for
subsequent seeding to T-dependent areas of lymph nodes, spleen, and other
lymphoid tissues throughout the body. The thymus can be identified at low
magnification (A) from the lobulation with cortex and medulla in each lob-
ule and the absence of germinal centers. At high magnification (B) the pres-
ence of Hassall’s (thymic) corpuscles is an identifying characteristic. Hassall’s
corpuscles contain degenerating epithelial cells in concentric arrays that
increase with age and instruct thymic dendritic cells to induce development
of regulatory T cells (Treg). The thymus is derived from the third and fourth
branchial pouches, notthe third branchial arch (answer c).Production of
memory B cells as well as effector and memory T cells occurs in the sec-
ondary lymphoid organs. Production of antibodies is the responsibility of
plasma cells, which arise from B lymphocytes and are found in germinal cen-
ters in lymph nodes throughout the body as well as in the spleen and tonsils
(answer a).The lymph nodes filter the lymph and blood, (answer b).The
spleen is the site of erythrocyte degradation and bilirubin recycling (answer e).
171.The answer is d.(Alberts, pp 1393–1394, 1401–1402, 1419. Kindt,
pp 223–225, 231–235, Abbas, pp 63–66, 70–73.)T cell gene rearrangement
occurs during the education of T cells in the thymus in fetal and early
neonatal development. The T cell receptor (TCR) is composed of αandβ
chains. Each chain contains a variable amino-terminal portion and a con-
stant carboxyl-terminal portion. These chains are encoded for by V, D, J,
and C gene segments, which undergo rearrangement during development