SPHK1 and infection: Whereas, in PMNs the response to the Ctr infection is characterized by a strong upregulation of SPHK1, at both early (2 h) and late (24 h) infection time points, in M2Φ two counteracting pathways involving upregulation of SPHK1 as well as SGPP1 and SGPL1 likely maintain a steady pool of S1P.