Blood Cells - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 90

Basophils are similar to mastocytes, but distinct. In normal conditions, they
are not detected in the blood circulation. 68 Basophils differ from mastocytes
and eosinophils, as they do not express plasmalemmal stem cell factor receptor
(SCFR) 69 and chemokine receptor CCR3, respectively. Human basophils also
express TLR2 and TLR4 Toll-like receptors.
The behavior of basophils in vivo can differ from that in vitro. Moreover, func-
tioning differences exist between mammal species. For example, mouse basophils
express peptidase-activated receptors, but human basophils do not. Basophils can be
activated by many agents, such as cytokines, immunoglobulins, peptidases, TLR2
ligands, and parasite-associated antigens.
Committed basophils release 2 kinds of mediators: (1) preformed granule-
associated mediators, such as vasodilator histamine, serotonin, bradykinin, anti-
coagulant heparin, and cytokines; and (2) newly generated mediators, such as
prostaglandins and leukotrienes. Both transmembrane ectonucleotide pyrophosph-
atase-phosphodiesterase ENPP3 (or CD203c) and Tspan30 (or CD63) are markers
of activated human basophils.
Basophils release numerous potent inflammatory mediators from their cytoplas-
mic granules upon high temperature, mechanical stress, ionization, toxins, pepti-
dases, cationic proteins derived from eosinophils and neutrophils, IgE-mediated
processes as well as IgE-independent immune mechanisms, such as that primed
by complement factors.
Low-molecular-weight mediators include histamine, serotonin, prostaglandins,
leukotrienes. These mediators are released in response of allergens. They cause
increased vascular permeability, smooth muscle constraction, vasodilation.
Basophils are the main source of interleukin-4 in allergen- and helminth-
activated blood mononuclear cells [ 174 ]. Basophils highly express IL33 receptor
(IL33R or IL1RL1) and produce IL4 and IL13 in response to IL33, a member of
the IL1 family, using MyD88 adaptor [ 173 ]. Interleukin-33 provokes airway hyper-
responsiveness and goblet cell hyperplasia. Activated basophils not only secrete
cytokines (Tables 3.9 and 3.10 ) to support the development of IL4-producing CD4

+
T lymphocytes and IgE-secreting B lymphocytes associated with type-2 helper T
immunity, but also produce chemoattractants for eosinophils and neutrophils into
inflammatory sites. 70 Ligands of TLR2 induce nuclear translocation of transcription
factor NF

B and cytokine secretion. On the other hand, TLR4 ligand lipopolysac-
charides remain inactive, as CD14 is not expressed by basophils [ 173 ].

κ

68 In addition to basophil progenitors, bipotent basophil-mastocyte progenitors in the mouse spleen
are able to differentiate into either basophils or mast cells [ 173 ].
69 A.k.a. cellular kinase in tyrosine cKIT or KIT and CD117.
70 Signals from T-cell receptors are strengthened by simultaneous binding of MHC molecules to
a specific coreceptor. The coreceptor corresponds to CD4 and CD8 on CD4 + and CD8 + T cells,
such as helper and cytotoxic T cells, respectively. Coreceptors CD4 and CD8 tether class-2 and -1
MHC molecules, respectively.