SPHK1 and allergic asthma: The S1P/S1PR signaling was regulated through the activation of SPHK1 and SPHK 2 to produce S1P by the phosphorylation of sphingosine (Nayak et al., 2010; Aarthi et al., 2011) and the airway hyperresponsiveness and inflammation was potentially reduced by SPHK inhibitors and FTY720, a synthetic analog of S1P and S1PR agonist (Aarthi et al., 2011) and other S1PR modulators (Marciniak et al., 2018), in animal models of allergic asthma (Sawicka et al., 2003; Idzko et al., 2006; Price et al., 2013).