6.0 Alternative options for in vitro mast cell studies
Apart from the mentioned cell lines, there are also other alternative options for in vitro mast cell studies in allergy albeit not as commonly reported. One of them is the Immortalized Human Mast Cell Line (LUVA). This cell line was first identified and characterized by Laidlaw and her collegues in 2011 114. The cells were grown from CD34+-enriched mononuclear cells derived from the peripheral blood of a donor with aspirin exacerbated respiratory disease114. The authors mentioned that this cell line can be maintained without stem cell factor to survive and proliferate without further addition of any growth factors for approximately 2 years. In addition, LUVA cells also display high levels of normally signaling c-kit, metachromatic cytoplasmic granules, and FcεRI114. These cells will prove valuable for functional human mast cell studies as they can be induced to degranulate and release various allergic mediators such as β-hexosaminidase, prostaglandin D2, thromboxane A2, and MIP-1β.
Another human mast cell line that is suitable for allergy studies is the ROSAKIT mast cells. This cell line was first reported in 2014 115. Unlike LUVA cells, these cells require stem cell factor to survive and proliferate with a doubling time of 24 h115. ROSAKIT cell also has functional IgE receptors which allows it to be easily activated to release mediators whenever FcεRI crosslinking happens115. Apart from activation through IgE receptors, this human mast cell line can also be induced by means of calcium influx. A reported study showed that the ROSAKIT cell induction using calcium ionophore A23187 was able to release 80% of β-hexosaminidase as compared to using IgE-FcεRI which only releases approximately 38% of the enzyme after 1 h induction115.
Apart from that, secondary mast cell lines from mouse origin such as MC/9 and P815 cell lines are also available. The MC/9 is a cloned mast cell line derived from the fetal liver of a (B6 × A/J)F1 mouse116. These cells can be sensitized to specific antigens by incubating them with IgE having the desired antigenic specificity, resulting in the release of soluble mediators such as histamine and leukotrienes when induced 117. A reported study by Jin et al. (2019) has also induced these cells using PMA (50 nM) and A23187 (1 μM) for 24 h to measure the release of histamine and LTC4 levels 118. P815 cells, on the other hand were isolated from a mouse with mastocytoma in 1957118,119. These cells do not express the IgE high affinity receptor and, therefore, can only be activated independent of the IgE pathway. However, they do express fragment crystallizable gamma receptor II (FcγRII) and could bind the Fc portion of mouse IgG antibodies through their fragment antigen-binding (Fab) which may recognize NK cells activating receptors leading to target cell lysis120. In addition, one study reported the use of C48/80 and CI to induce degranulation in P815 cells to release allergic mediators such as IL-4 and histamine 121.