- D1.532 - Phenotypic and Functional Comparison of LAD2, HMC-1.2, and Primary Human Mast Cells

Mast cell (MC) models are essential to study MC biology, function and therapeutic responses. Commonly used cell lines include HMC-1.2, LAD2 as well as primary tissue-derived MCs. However, these models differ substantially in receptor levels and function which can affect experimental outcomes. Therefore, appropriate MC model selection should be aligned with the scientific question. We systematically compared primary human skin-derived mast cells (hsMCs) with established MC lines to define their biological and functional profiles.

HMC-1.2 cells were obtained commercially, and LAD2 cells were provided by the NIAID/NIH (USA). Primary hsMCs were isolated from skin samples and utilized the day after isolation. Receptor profiles were evaluated by flow cytometry, and degranulation in response to anti-IgE, ionomycin, Substance P and Compound 48/80 was measured via beta-hexosaminidase release.

MC receptors exhibited distinct expression profiles across the studied groups. CD117 (cKit) was highly expressed in HMC-1.2 (99.6%) and LAD2 (99.3%) and lower in hsMCs (82.3%). FcεRIα expression was low in HMC-1.2 (0.4%), intermediate in LAD2 (62.0%), and highest in hsMCs (96.8%). MRGPRX2 expression was almost absent in HMC-1.2 (0.2%), but highly expressed in LAD2 (100.0%), and hsMCs (97.3%). While low affinity IgG receptor: CD32 (FcγRIIa) expression was detectable in all models (HMC-1.2: 67.1%, LAD2: 100.0%, hsMCs: 82.9%), basal CD63 (LAMP3) levels were markedly higher in HMC-1.2 (89.7%) compared to LAD2 (7.0%) and hsMCs (6.2%). In functional assays, assessing CD107a expression, anti-IgE stimulation induced robust activation in primary hsMCs (56.9% vs. 12.0% baseline) and beta-hexosaminidase release but failed to activate LAD2 (6.3% vs. 2.6% baseline) or HMC-1.2 (1.0% vs. 0.0% baseline) cells. Conversely, the MRGPRX2 agonist Substance P triggered strong activation in both LAD2 (85.6%) and hsMCs (71.6%) -accompanied by degranulation- while HMC-1.2 cells remained unresponsive.

Distinct receptor and activation profiles were observed across MC models. These findings have important implications for selecting the appropriate mast cell model for functional studies: primary hsMCs are optimal for FcεRI-mediated studies, whereas LAD2 and hsMCs are more suitable for MRGPRX2-driven pseudo-allergic responses. HMC-1.2 cells are unsuitable for activation studies but may be used for cell proliferation studies due to their rapid growth characteristics.