3.2 Inducers and mediators release for HMC-1 cells
As the HMC-1 cell line lacks the expression of FcεRI, an external
stimulus is required to induce mast cell degranulation. The combination
of PMA and CI is widely used (25 of 50 and 28 of 50 respectively). Other
inducers include OVA, IL-33, TSLP, protein kinase activator C, RANKL,
LPS, histamine, and more. However, three of the 50 publications did not
specify the type of inducers used. The induction time implemented by
most studies falls within 5 to 8 hours (h) (23 of 50), followed by an
hour and below (20 of 50), within 13 to 24 h (16 of 50), 2 to 4 h (13 of
50) and 9 to 12 h (2 of 50). However, four publications did not indicate
the induction time. The degranulation of mast cells can be characterized
by the concentration of cytokines secreted. Many of the publications
studied the release of TNF-α (29 of 50), IL-6 (27 of 50), IL-1β (20 of
50), histamine (17 of 50), TSLP (14 of 50), and IL-8 (12 of 50). Table 2
summarizes our analysis of the type of inducers, induction time, and
type of mediators often studied by researchers using HMC-1 cells.
Mast cell activation depends on the cross-linking of IgE antibodies on
the FcεRI and the subsequent signal transduction cascade, including
intracellular Ca2+ mobilization, influx, and
protein kinase C (PKC)
activation. As such, the combination of PMACI is a strong candidate as
an inducer owing to its ability to enhance Ca2+ influx
and activation of MAP kinases 35,36. PMA stimulates
PKC activity, while CI raises the intracellular level of
Ca2+ 37,38. Many clinical studies
have shown the upregulation of cytokines released (Th1-related
cytokines) upon PMACI stimulation, namely the IL-2, IL-6, IL-17, IFN-γ,
and TNF-α. However, these studies did not affect the expression of IL-4
and IL-10 39–41. Another point to note in future
research is that the expressions of IL-10, IL-17, IL-22, IFN-γ, and
TNF-α are higher in IMDM than RPMI-1640 upon PMACI stimulation due to
the concentration of Ca2+. According to Zimmermann and
his colleagues (2015), IMDM consists of 1.49 mM of
Ca2+, while RPMI-1640 contains 0.42mM of
Ca2+. Therefore, by increasing the
Ca2+ concentration in RPMI-1640 to 1.5 mM, the
expression of cytokines is comparable to IMDM. Vice versa, the reduction
of Ca2+ concentration in IMDM resulted in a lowered
cytokine expression. Thus, implying that 1.5 mM of
Ca2+ is optimal for maximal ionomycin stimulation in
cells 42.
When compared between PMACI, lectin phytohaemagglutinin (PHA), LPS,
Con-A, and pokeweed mitogen, PMACI expresses the most potent cytokine
production in a short period without significant damage to the cells43. On the other hand, C48/80 acts as a ”selective”
mast cell activator by stimulating the trimeric G-proteins and
activating phospholipase C and D pathways 44. C48/80
activation can bypass Ca2+ and PKC signal
transduction, thus beneficial when PMACI cannot be used35.