SPP1 and systemic lupus erythematosus: Specifically, SPP1 is involved in the transcription of genes in monocytes and production of cytokines in innate immune cells in SLE (Ghodke-Puranik et al., 2021), while PHC2 inhibits interleukin-2 secretion and acts as a negative regulator of Th-cell activity (Cho et al., 2013).