d. Maturation of B cells in humans takes place first in the fetal liver and later in
the bone marrow of the adult.
e. At various stages of maturation, a B cell expresses unique markers on its
surface that are characteristic of a particular developmental stage. Examples include
IgM and IgD, and Fc markers. Monoclonal antibodies can be used to detect B-specific
a. The macrophage is a relatively large, phagocytic cell that belongs to a family
of cells that are collectively referred to as "mononuclear phagocytes." They play an
essential role in many different types of immune and inflammatory reactions.
Macrophages are unique in that unlike most cell types, they have multiple diverse
functions. They are important effector cells in killing intracellular parasites and tumor
cells; they act as scavengers for foreign material and extracellular debris; and they act
as regulators of immune responsiveness.
b. The major functional roles of macrophages in the immunological process are
antigen processing and antigen presentation.
c. An additional function attributed to macrophages is the production of factors
that influence the activity of lymphocytes. Macrophages secrete over 50 products,
many related to immunity. These include enzymes, plasma proteins (including
coagulation proteins and complement components), lipids, and factors regulating
cellular functions. One of the factors regulating cellular functions is interleukin-1, which
has a number of important effects. For example, interleukin-1, also called lymphocyte-
activating factor (LAF), induces lymphocytes to produce interleukin-2, which in turn
encourages short-term proliferation of lymphocytes.
Section II. B CELLS AND HUMORAL IMMUNITY
ANTIGEN PROCESSING AND PRESENTATION
a. Antigen bound to macrophage surfaces or internalized by macrophages is
more immunogenic than antigen that has not been "processed" by macrophages.
Macrophages function in processing the antigen and subsequently presenting it to
lymphocytes. It is thought that processing may expose determinants otherwise not
available or change pre-existing determinants into a recognizable form.
b. Once the antigen is processed by the macrophage, it is presented to
lymphocytes. There is evidence that small amounts of antigen bound to the
macrophage surface are important in the induction phase of the immune response.
Evidence also suggests that macrophage processing is not essential for all antigens.
The size of the antigen may determine whether macrophage processing is necessary.