Natural interferon-producing cells in mice.

When mouse lymphoid cells derived from untreated C57BL/6 mice were cocultivated in liquid cultures with L-cell monolayers for 3 h, overlaid with soft agar, and then further incubated for 12 h, protected foci of L cells against vesicular stomatitis virus infection were formed. Many strains of mice have been found to have the protected focus-forming cells on the L-cell monolayers. The formation of the protected foci was completely suppressed by addition of cycloheximide into soft agar. When anti-interferon (type I) antiserum was added to soft agar, there was a decrease in focus counts of about 80%. These experimental results indicated that the formation of protected foci by untreated mouse lymphoid cells was mediated for the most part by type I interferon that was produced without addition of special inducer. We have designated these focus-forming cells as natural interferon-producing cells (NIPC). NIPC belong to the glass-adherent fraction, and Thy-1 antigen, immunoglobulin, and Ia antigen could not be detected on the surface of the NIPC. NIPC were detected in congenitally athymic nude mice. These findings suggest that NIPC belong to the Ia-negative macrophages. Mouse lymphoid cells obtained from germfree mice could form the protected foci on L-cell monolayers and could produce interferon without the addition of a special inducer. NIPC are considered to be a cellular background for spontaneous interferon production.