B and T Lymphocyte Attenuator is a Target of miR-155 during Naïve CD4+ T Cell Activation.

BACKGROUND: MicroRNA-155 (miR-155) is upregulated during T cell activation, but the exact mechanisms by which it influences CD4+ T cell activation remain unclear.
OBJECTIVE: To examine whether the B and T lymphocyte attenuator (BTLA) is a target of miR-155 during naïve CD4+ T cell activation.
METHODS: Firefly luciferase reporter plasmids pEZX-MT01-wild-type-BTLA and pEZX-MT01-mutant-BTLA were constructed. Lymphocytes were nucleofected with miR-155 inhibitor or negative control (NC). Then, naïve CD4+ CD62L+ helper T cells purified from lymphocytes were stimulated with immobilized antibody to CD3 and soluble antibody to CD28. miR-155 and BTLA expression were examined by real-time RT-PCR. Cell surface CD69 expression and IL-2 secretion were measured by ELISA and flowcytometry, respectively.
RESULTS: Luciferase reporter assay showed that miR-155 targeted the BTLA 3'UTR region. Compared with non-stimulated condition, both miR-155 and BTLA mRNA expression were upregulated after T cell activation. Similar results were observed for BLTA protein expression. Compared with NC, the miR-155 inhibitor decreased miR-155 by about 45%, but did not influence BTLA mRNA expression. Compared with NC, the miR-155 inhibitor decreased the surface BTLA expression by about 60%. Upregulation of BTLA in miR-155 knockdown CD4+ T cells did not influence the cell surface expression of CD69, an early activation marker (p=0.523). Similarly, IL-2 production was not changed.
CONCLUSION: miR-155 is involved in the inhibition of BTLA during CD4+ T cell activation. These results might serve as a basis for an eventual therapeutic manipulation of this pathway to treat inflammatory and autoimmune diseases.