Liability to hydrophobic and charge interaction of smooth Salmonella typhimurium 395 MS sensitized with anti-MS immunoglobulin G and complement

Sensitization of smooth Salmonella typhimurium 395 MS bacteria with hyper-immune anti-MS immunoglobulin G (IgG) antibodies increased the liability to hydrophobic interaction as assessed by the affinity for a column of Octyl-Sepharose. After sensitization, the material originally eluted with 1 M (NH4)SO4 in a 0.01 M phosphate buffer (pH 6.8) was not desorbed until the ionic strength was reduced to nil, and 0.1% (vol/vol) Triton X-100 in the 0.01 M phosphate buffer was used as eluant. Furthermore, by including positively charged bis-trimethylamino-polyethylene glycol (PEG) or negatively charged bis-sulfoamino-PEG in an aqueous two-phase system of dextran T500 and PEG 6000, the partition of the IgG-sensitized bacteria was affected by either of the polymers, whereas that of the parent bacteria was not. The hydrophobic effect of IgG binding was enhanced by complement. With heat-inactivated complement, the effect of IgG was diminished. The F(ab')2 fragment showed a much lower capacity to promote a hydrophobic interaction than the complete IgG molecule.