Soluble CD86 is a costimulatory molecule for human T lymphocytes

CD86 is an important costimulatory molecule for the priming and activation of naive and memory T cells, respectively. Here, we show that soluble CD86 is detected in human serum. Soluble CD86 is produced by resting monocytes and results from an alternatively spliced transcript (CD86 Delta TM) characterized by deletion of the transmembrane domain. Recombinant CD86 Delta TM binds to CD28 and CTLA-4 and induces the activation of T cells after stimulation with anti-CDS mAb. CD86 Delta TM also induces IFN gamma production by virus-specific CD8(+) memory human T cells stimulated with the Flu M1 peptide. The concentrations of soluble CD86 found in human serum are sufficient to induce biological activity. Soluble CD86 molecule, therefore, appears to be a functional costimulatory molecule playing a potentially important role in immune surveillance.