Basic studies on the biological functions and possibilities of clinical applications of an intestinal IgG Fc binding site.

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Intestinal mucus is very important in protecting the intestinal mucosa against various harmful antigens, however the mechanisms involved are incompletely defined. Recently, we identified a binding site for the Fc region of IgG(FcIBS) associated with goblet cell mucin in human intestine. We documented that FcIBS could bind antibodies-bacterial complexes. This time we investigated the following biological functions of FcIBS and tried to establish recombinant FcIBS.1) Establishment of recombinant FcIBS : Human colonic epithelium were separated from colonic mucosa. Fraction of mRNA was gained from poly(A) fraction of the colonic epithelia extract. This fraction containing mRNA was injected into the ovum of Xenopus leavis and translated into FcIBS protein. However we could not make cDNA of FcIBS.2) Effect of FcIBS on growth of bacteria : Culture of RDEC-1 both in the presence of anti-RDEC-1 IgG and 10K supernatant of colonic homogenate resulted in a significant reduction of colony number in growth of bacteria. Culture of human pathogenic E.Coli(0111) or Salmonella typhimurium(04) both in the presence of anti-bacterial IgG and 10K supernatant of colonic homogenate has resemble results to that of RDEC-1. These results suggested that FcIBS may play a role in preventing bacteria from attaching to the epithelial surface of the intestine. 3) Inhibition of complement binding by FcIBS : When anti-sheep red blood cells (SRBC) IgG were pre-incubated with affinity-purified FcIBS, the ability of the antibodies to lyse SRBC in the presence of complement was inhibited significantly. These results suggested that FcIBS may interfere the activation of complement and the tissue injury associated with immune complex formation on the epithelium.