and, therefore, is less condensed than the chromatin of a lymphocyte (F).
The monocyte has some phagocytic activity in the blood, but its major role
is as a source of macrophages throughout the body including Langerhans
cells (skin), microglia (brain), and Kupffer cells (liver).
Megakaryocyte. The megakaryocyte (E)is a large cell with a multi-
lobular appearance and is the source of platelets. Megakaryocytes fragment
to form the platelets, which are key elements of the blood.
Lymphocyte.The lymphocyte (F)is considered an agranular cell with
an ovoid nucleus and scanty cytoplasm. The shape and the arrangement of
chromatin vary, depending on the classification of the lymphocyte: small,
medium, or large. Small and medium are involved in chronic inflamma-
tion, whereas, large lymphocytes are the source of T and B cells. Lympho-
cytes are either T or B cells based on their education in the thymus or bone
marrow. Plasma cells differentiate from B lymphocytes that undergo mito-
sis and form a plasma cell and a memory cell after exposure to appropriate
antigen. An antigen-presenting cell and a specific subtype of T lymphocyte
called a helper T cell are required for B cell differentiation into antibody-
producing plasma cells.
166.The answer is e.(Junqueira, pp 229, 231. Ross and Pawlina, pp
257–258. Kasper, pp 349, 351, 356.)The patient returning from a camping
trip most likely has contracted a parasite. The cell in the transmission elec-
tron micrograph is an eosinophil. Eosinophil granules contain a number of
important substances including histaminase, eosinophil peroxidase,
eosinophil cationic protein, and major basic protein (MBP). MBP forms the
core of the eosinophilic granules and is a toxin for parasites. MBP binds to
and disrupts the membrane of the parasite. The binding is mediated by the
Fc receptor. MBP also causes basophils to release histamine. Eosinophils
phagocytose parasites, but MBP is not directly involved (answer a).IL-1
and IL-2 carry out the functions of activating APCs and stimulating prolif-
eration of B- and T-cells, respectively. However, the eosinophil does not
release IL-1 and IL-2 (answers b and c).IL-5 stimulates production and
maturation of eosinophils, but is not released by eosinophils (answer d).
Cardiovascular System, Blood, and Bone Marrow Answers 269