CD28 and systemic lupus erythematosus: Research indicates that SRSF1 can suppress mTOR pathway activity by upregulating PTEN expression in naive CD4 + T cells from systemic lupus erythematosus patients.24–26 We examined PTEN protein expression, a negative regulator of the mTOR pathway, and found that PTEN levels decreased while phosphorylated S6 (pS6) protein levels increased in CD8+T cells following anti-CD3 and anti-CD28 stimulation in Srsf1fl/flCd4-Cre mice (Fig. 3g), suggesting heightened mTORC1 pathway activity.