284 Anatomy, Histology, and Cell Biology
175.The answer is a.(Young, pp 203, 207–221. Junqueira, pp 258, 268,
271, 272, 274. Kindt, pp 29–30, 494–498. Abbas, pp 211–213.)Martin
Causubon suffers from severe combined immunodeficiency (SCID) and
has no T cells. The CD3 antibody recognizes a group of five proteins that
are associated with the α andβchains of the T cell receptor (TCR). Recog-
nition of antigen-MHC by the TcR-CD3 complex does not require any
other molecules. Other “accessory molecules” on T cells (THor Tc) and
their partner ligands on APCs or target cells provide a “second signal” to
stimulate T cells. The region shown is a T-dependent region of the spleen.
The photomicrograph shows an area of white pulp with a central artery.
The sheath surrounding the central artery is known as the periarterial lym-
phoid sheath (PALS) and is analogous to the deep cortex (paracortex) of the
lymph node or the interfollicular zone of Peyer’s patches, the other T-
dependent regions within lymphoid tissue.
The histologic structure of the spleen includes the presence of a connec-
tive tissue capsule with extensions into the parenchyma, forming trabeculae.
The parenchyma consists of red pulp, which represents areas of red blood
cells, many of which are undergoing degradation and phagocytosis by
macrophages lining the sinusoids of the red pulp, and white pulp, which rep-
resents lymphocytes involved in the filtration of the blood. The germinal cen-
ters within the white pulp are the B-dependent regions of the spleen.
(The Case of Martin Causubon is provided courtesy of the Jeffrey Modell
Foundation and “The Primary Immunodeficiency Resource Center:” http://
http://www.info4pi.org/patienttopatient/index.cfm?section=patienttopatient&c))
176.The answer is b.(Abbas, pp 68–69, 133–136. Kindt, pp 372–375. Kasper,
pp 1912, 1916, 1947–1948. Junqueira, pp 97–101. Alberts, pp 1208–1211.)The
patient in the scenario suffers from peanut allergy. Allergic reactions involve
IgE produced by plasma cells (shown in the fluorescein-labeled micrograph)
in the germinal centers of the lymph nodes or spleen (answers c and d).
Allergens, like peanut antigen, are originally recognized by T cell receptors on
TH2 cells. The TH2 cell produces IL-4 which stimulates B cells to differentiate
into plasma cells (like those in the photomicrograph), which synthesize and
secrete IgE. IgE binds specifically to the high affinity receptor, Fc epsilon RI,
on mast cells and basophils. The presence of IgE primes the mast cell; it is
thencapable of an allergic response by secreting histamine and heparin
when the child is again exposed to the allergen (peanut antigen). Histamine
alters vascular permeability leading to edema and in severe cases to anaphylaxis.
Differentiation of IgE-plasma cells is regulated by the low affinity IgE receptor,