Surface-exposed protein antigens of the gonococcal outer membrane.

Whole, 125I-labeled gonococci (GC) were incubated with rabbit sera against whole GC. After washing, the [125I]GC were lysed in detergent, and radioiodinated antigen-antibody complexes were immunoprecipitated by protein A-Sepharose. Several GC outer membrane proteins, including proteins I, II, and III, could be identified in immunoprecipitates obtained with these antisera. In many immunoprecipitates, a 44K protein was present. Reactivity of antisera toward protein II could be demonstrated, and some rabbit sera contained very prominent apparent antibody activity toward this protein. Proteins I and III were found in similar ratios in immunoprecipitates, suggesting that they form heteropolymers in GC outer membranes. Qualitative and quantitative difference in antibody reactivity and specificity could be demonstrated with serially obtained sera from rabbits immunized with whole GC. The use of viable or Formalin-fixed heat-killed staphylococci yielded "non-immunological" precipitation of 125I-labeled GC constituents; this occurred with staphylococci regardless of whether they contained protein A.