Autoinhibition of Rheumatoid Factor Reactivity Demonstrated by a Block Hemagglutination Procedure

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Abstract
Summary: Various rheumatoid factor (RF) sera were titrated with human γ-globulin (HGG) coated tanned sheep cells at six cell concentrations ranging from 0.125% to 2.0%. It was found that in 36 of 63 sera tested there was an abnormally large decrease in titer with increasing cell concentration. Double logarithmic plots of titers vs. cell concentrations were linear. While linearity with a slope of -1.0 was to be expected, it was found that these 36 sera tested yielded slopes greater than -1.0. Addition of aggregated HGG to a -1.0 slope serum caused a rise in slope. Removal of autologous 7 S HGG, by diethylaminoethyl (DEAE) column chromatography, from a high slope serum lowered the slope. Addition of 7 S HGG, prepared either from a high slope serum or from certain normal sera, to a -1.0 slope serum served to raise the slope. Partial removal of RF by adsorption of a low slope serum also caused an increased slope. Heating at 56°C for 30 min did not affect slope values. These results suggest that the high slope effect is primarily due to autoinhibitory heat stable components present in the 7 S HGG fraction of most rheumatoid factor sera.