SELPLG and systemic lupus erythematosus: Moreover, variations in the upstream region of P-Selectin are a risk factor for SLE, and two risk alleles have been identified potentially affecting the transcription of P-Selectin and the binding to P-Selectin glycoprotein ligand-1 (PSGL-1)15, the main ligand for P-Selectin expressed on all leukocyte subsets, and also a ligand for E- and L-Selectin3, 17, 18, 19.