Proteins adhering to Escherichia coli after exposure to guinea-pig serum.

The constituents of guinea-pig serum that attach to the surface of a serum-sensitive strain of have been determined. Antisera from rabbits immunized with bacteria exposed to serum (`sensitized' bacteria) were analysed by means of immunoelectrophoresis. It is concluded that at least seven constituents from the serum of the normal adult guinea-pig adhere to the during sensitization. These bind tightly enough to resist removal by at least six washings of the sensitized bacteria. Two of these constituents (IgG and IgM) are known to possess antibody activity. A third constituent, β, is known to be the third component of the complement system of the guinea-pig. Another is probably the fourth component of this complement system. The other three serum components remain unidentified, although one of them is shown to possess esterase activity, and thus may be related to the first component of complement. Evidence is presented suggesting that normal guinea-pigs may have little or no antibody against present in the IgG fraction of the serum. If, before sensitization of the , the serum is heated to inactivate the activity of bactericidal complement, the serum does not kill this organism, but no change is detectable in the serum proteins adhering to these bacteria. Similarly, if, before sensitization of , the bactericidal antibody to the is absorbed from the serum, while bactericidal complement is left intact, there is no change in the serum proteins adhering to the bacteria. When the serum used for sensitizing is from guinea-pigs that have been actively immunized with the same strain of , rabbits immunized with these sensitized bacteria appear to form increased amounts of antibody directed against the 7S γ-globulin of the guinea-pig serum.