Lymphatic System and Immunity
with T cells and are abundant in lymph nodes, the spleen,
bone marrow, and the intestinal lining
(f g. 16.16)
Each person has millions of varieties of T and B cells.
The members of each variety originate from a single early
cell, so they are all alike, forming a
¯n) of cells
(genetically identical cells originating from division of a sin-
gle cell). The members of each variety have a particular type
of antigen receptor on their cell membranes that can respond
only to a speciF
compares the charac-
teristics of T cells and B cells.
What is immunity?
What is the dif
erence between an antigen and a hapten?
How do T cells and B cells originate?
T Cells and the Cellular Immune Response
A lymphocyte must be activated before it can respond to an
antigen. T cell activation requires processed fragments of
antigen attached to the surface of another type of cell, called
in red bone
the bone marrow
to become B cells.
processed in the
thymus to become
Both T cells and B cells
are transported through
the blood to lymphatic
organs, such as the
lymph nodes, lymphatic
ducts, and spleen.
Falsely colored scanning electron micrograph o± a
circulating lymphocyte (8,600×).
Bone marrow releases relatively unspecialized lymphocyte precursors, which a±ter
processing specialize as T cells (T lymphocytes) or B cells (B lymphocytes). In the ±etus, the medullary cavity
contains red marrow.