| Heat-inactivated normal human serum produces iron-reversible bacteriostasis of a number of microoganisms. This inhibitory affect was abolished by adsorption of serum with ultraviolet-killed cells of species that produce the siderophore enterochelin. Bacteriostasis was also alleviated by adsorption of serum with 2,3-dihydroxy-N-benzoyl-L-serine, a degradation product of enterochelin, bound to the insoluble matrices AH-Sepharose 4B or Affigel 701. The adsorption process did not add iron or enterochelin to serum, nor did it remove transferrin. The immunoglobulin fraction from normal human serum was isolated; when added to a defined medium prepared so as to mimic human serum, the immunoglobulin rendered the medium inhibitory to an enterochelin-defective strain of Salmonella typhimurium. Adsorption of this medium with AH-Sepharose 4B-2,3-dihydroxy-N-benzoyl-L-serine (AHS4B-DBS) removed this inhibition.;The enterochelin-specific immunoglobulin antibody could also be isolated by affinity chromatography of serum with AHS4B-DBS. When added to a whole cell radioactive iron uptake system, the antibody inhibited enterochelin-directed uptake but not that mediated by citrate or ferrichrome. Also, the growth stimulatory effect of enterochelin on an Ent('-) strain of Escherichia coli was blocked by immunoglobulin. This antibody has a high affinity for enterochelin; various elution procedures employing high salt concentrations and low pH failed to remove it from affinity columns. Elution with 3 M sodium thiocyanate or 13 mM 2,3-dihydroxybenzoic acid proved successful. Two pieces of evidence indicate that the enterochelin-specific antibody is primarily of the IgA isotype. It could be removed from serum with goat antihuman IgA and was present only in sodium sulfate fractions of serum known to contain IgA. These results indicate that an enterochelin-specific IgA immunoglobulin exists in normal human serum. These immunoglobulins may act synergistically with transferrin to effect bacteriostasis of enterochelin-producing pathogens.;The ability of UV-killed cells to remove the antibody from serum suggested that enterochelin was firmly bound to the cell surface. The failure of E. coli ompB strains, which are phenotypically lacking the porin proteins b and c, to remove the antibody indicated that enterochelin was bound to either b or c. However, serum adsorbed with b('-), c('-), or b('-)c('-) (ompF, ompC) strains did not contain the antibody indicating that enterochelin was still bound to the cell surface of these strains. These results suggested that the regulatory gene ompB controls the synthesis of more than just the porin proteins. Some of these other proteins may be involved in iron assimilation. |
