Human cells allosensitized in vitro release soluble suppressor factors: presence of at least two distinct factors.

Human cells allosensitized in vitro release suppressor "factors" (SF) capable of inhibiting a primary mixed lymphocyte reaction (MLR). Preincubation experiments with SF of either responders or stimulators in MLR suggested the presence of at least two distinct suppressor activities: one called SFR, acting on certain responders including the SF producer; the other called SFNR, acting on stimulators in all MLR. These activities can be separated using sorbents composed of monoclonal anti-HLA-DR antibodies on the one hand and mouse or rabbit IgG on the other hand. SFR is found in the effluent and SFNR in the eluate of these sorbents. The SFNR-binding properties are shared by a murine suppressor factor called immunoglobulin-binding factor or IBF. Moreover SFNR, like IBF, is capable of suppressing a secondary in vitro IgG response through the species barrier.