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 a nd results from an alternatively spliced transcript (CD86 Delta TM) charact erized by deletion of the transmembrane domain. Recombinant CD86 Delta TM b inds to CD28 and CTLA-4 and induces the activation of T cells after stimula tion 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 pepti de. 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 rol e in immune surveillance.