AN EXAMINATION OF THE “STAR‐PHENOMENON”, A THREE COMPONENT IMMUNOPRECIPITATION INVOLVING STAPHYLOCOCCAL PROTEIN A

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Abstract
The co‐precipitation called “star‐phenomenon” occurred between the three component system: protein A, an IgG forming soluble complexes with protein A and F (ab') 2‐preparations of human IgG, guinea pig IgG or rabbit anti‐staphylococcal IgG. Co‐precipitation also occurred if the IgG was replaced by normal human Fc fragments. On a protein A column the human F(ab')2‐preparation was separated into a major non‐reactive and a minor reactive fraction. Only the latter contained Fc‐structures, these being isolated on an anti‐Fc column and found to belong to undigested IgG. The “star”‐forming, protein A reactive F(ab') 2‐fragments were washed through the anti‐Fc column. The F(ab')2 fraction from rabbit anti‐staphylococcal IgG contained no Fc‐structures and only a small portion containing anti‐protein A activity was active in co‐precipitation.