Selective Sparing of Human Tregs by Pharmacologic Inhibitors of the Phosphatidylinositol 3-Kinase and MEK Pathways

Phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase/extracellular signal-regulated (MEK) signaling are central to the survival and proliferation of many cell types. Multiple lines of investigation in murine models have shown that control of the PI3K pathway is particularly important for regulatory T cell (Treg) stability and function. PI3K and MEK inhibitors are being introduced into the clinic, and we hypothesized that pharmacologic inhibition of PI3K, and possibly MEK, in mixed cultures of human mononuclear cells would preferentially affect CD4(+) and CD8(+) lymphocytes compared with Tregs. We tested this hypothesis using four readouts: proliferation, activation, functional suppression, and signaling. Results showed that Tregs were less susceptible to inhibition by both δ and α isoform-specific PI3K inhibitors and by an MEK inhibitor compared with their conventional CD4(+) and CD8(+) counterparts. These studies suggest less functional reliance on PI3K and MEK signaling in Tregs compared with conventional CD4(+) and CD8(+) lymphocytes. Therefore, the PI3K and MEK pathways are attractive pharmacologic targets for transplantation and treatment of autoimmunity.

Splenic and peritoneal B-1 cells differ in terms of transcriptional and proliferative features that separate peritoneal B-1 from splenic B-2 cells

B-1 cells constitute a distinct B cell subset with characteristic phenotypic and functional features. B-1 cells are highly represented among peritoneal lymphocytes; substantial numbers of B-1 cells are also located within splenic tissue. Here a number of differences in transcription factor and gene expression were identified that separate peritoneal B-1 and splenic B-2 cells, and then splenic B-1 cells obtained from immunoglobulin transgenic mice were tested for these parameters. Splenic B-1 cells resembled splenic B-2 cells rather than peritoneal B-1 cells in terms of nuclear expression of DNA-binding STAT3, CREB, and PU.1, with respect to transcriptional activation of IL-10, and in the failure to enter cell cycle in response to PMA. Splenic B-1 cells (B-1S) appear to constitute a unique population of B-1 cells, which, while sharing with peritoneal B-1 cells (B-1P) certain phenotypic features, differ from them in transcription factor and gene expression and in signaling for cell cycle progression.