Chlorazol Fast Pink (CFP) is a sulfonic acid azo dye, first described as an in vitro complement inhibitor in 1952 (Lambert & Richley, B. J. Exp. Path. 33, 327, 1952). We have examined CFP in vivo and in vitro and found that it inhibits complement dependent lesions in laboratory rodents, and that these effects are correlated with depression of serum complement. In some cases, CFP has been compared with pentosan polysulfate (PPS), another anionic complement inhibitor.

CFP and PPS, injected intraperitoneally, block Forssman shock and Forssman cutaneous vasculitis in guinea pigs and the reverse passive Arthus reaction in guinea pigs and rats. Inhibition of these reactions is accompanied by an inhibition of serum complement, demonstrable by an assay of “undiluted” serum. In this assay, serum is laid over EA embedded in an agarose matrix in a capillary tube, and the zone of lysis measured with an optical micrometer.

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