Blood Cells - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 161

Plasmocytes yield humoral immunity by secreting antibodies against antigens
that confer a continuous existence of potential specific response. They constitute
a special pool of immunological memory cells. Short- and long-life plasmocytes
derive from memory B lymphocytes.
Stimulation of B cells by antigen causes either cell death or proliferation and
differentiation into plasmablasts . 167 Plasmablasts can develop from any type of
activated B cells: naive marginal-zone, naive follicular, activated germinal-center,
and memory B cells.
Plasmablasts express chemokine receptors CXCR4 to migrate to the bone
marrow, spleen red pulp, and medullary cords of the lymph nodes, where is
produced CXCL12 chemokine. On the other hand, plasmablasts repress synthesis
of chemokine receptors CXCR5 and CCR7 that control germinal-center migration,
hence avoiding a return to the sites of immune reactions.
Plasmocytes synthesize adhesion molecules, such as E- and P-selectin ligands,
α L -integrin (or CD11a),

β 2 -integrin (or CD18), and heparan sulfate proteoglycan

receptor epican. 168
Certain plasmablasts migrate to survival niches to maintain a concentration of
antibodies following resolution of the immune response, thereby protecting against
subsequent challenges. CD4

helper T cells bind antigens presented by B cells and
participate in clones of antibody-secreting plasmocytes.
In the spleen, 2 populations of plasmocytes exist: a long-life plasmocyte pool
and a set of rapidly renewing short-life plasmocytes. Most long-life plasmocytes
reside in the bone marrow. The development and survival of plasmocytes depend
on several factors: interleukins, such as IL6 and IL21; tumor-necrosis factor; the
transcription factor B-lymphocyte-induced maturation protein BLIMP1 encoded
by the positive-regulatory domain-containing Prdm1 gene; stable isoform of the
transcription factor X-box-binding protein XBP1; and suppression of transcription
factor of B-cell development paired box protein PAX5 [ 292 ].

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3.13 Monocytes and Macrophages

The myeloid cell lineage of innate immunity includes 2 distinct lineages of phago-
cytes: (1) monocytes and macrophages and (2) dendritic cells. Bone marrow-derived
myeloid cells — blood-circulating monocytes and tissue-resident macrophages —
are effectors and regulators of inflammation and immediate innate immunity. Den-
dritic cells initiate and regulate the pathogen-specific adaptive immune responses
and major effectors of the development of immunological memory and tolerance.

167 Plasmocyte precursors arise from terminal differentiation of B cells that is defined as the
switch from expression of plasmalemmal antibody, which acts as an antigen receptor, to antibody
secretion.
168 A.k.a. CD44, extracellular matrix receptor-3, and lymphocyte homing-adhesion receptor GP90.