Chloroquine inhibits the production of a mononuclear cell factor by inhibition of lectin binding.

The effect of chloroquine (CQ) on the ability of normal human peripheral blood monocytes to produce a soluble mononuclear cell factor (MCF) capable of stimulating prostaglandins from adherent rheumatoid synovial cells was studied. CQ inhibited concanavalin A (Con A)- and bacterial peptidoglycan-induced MCF activity, but not colchicine-induced activity, in a dose-dependent manner. After incubation with CQ for 20 minutes, 3H Con A binding was reduced by 50%, and metabolism of pre-bound 3H Con A was inhibited. These data suggest that CQ can inhibit MCF production by inhibition of lectin binding, perhaps by inhibition of receptor recycling.