Binding of Clostridium difficile toxin A to human milk secretory component

• Published in: Journal of medical microbiology Vol. 47; no. 10; pp. 879 - 888
• Main Authors: Dallas, S. D, Rolfe, R. D
• Format: Journal Article
• Language: English
• Published: Reading Soc General Microbiol 01-10-1998; Society for General Microbiology
• Subjects: Animals; Bacterial Toxins - immunology; Bacterial Toxins - metabolism; Bacteriology; Binding, Competitive; Biological and medical sciences; Clostridium difficile; Colostrum - immunology; Cricetinae; Electrophoresis, Polyacrylamide Gel; Enterotoxins - immunology; Enterotoxins - metabolism; Fundamental and applied biological sciences. Psychology; Glycosylation; Guanylate Cyclase - immunology; Guanylate Cyclase - metabolism; Humans; Immunoglobulin A, Secretory - chemistry; Immunoglobulin A, Secretory - immunology; Immunoglobulin A, Secretory - metabolism; Intestine, Small - metabolism; Microbiology; Microvilli - metabolism; Milk, Human - immunology; Milk, Human - metabolism; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Receptors, Enterotoxin; Receptors, Guanylate Cyclase-Coupled; Receptors, Peptide - immunology; Receptors, Peptide - metabolism; Secretory Component - immunology; Secretory Component - isolation & purification; Secretory Component - metabolism; Secretory component; Human; Immunoglobulins; IgA; Clostridium difficile; Clostridiales; Host agent relation; Molecular interaction; Toxin; Clostridiaceae; Secretory protein; Human milk; Bacteria; Colostrum; Biological receptor
• ISSN: 0022-2615; 1473-5644
• DOI: 10.1099/00222615-47-10-879

Department of Microbiology and Immunology, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
1 Corresponding author: Dr R. D. Rolfe.
Received October 13, 1997
Accepted January 21, 1998
Toxigenic Clostridium difficile is isolated from a majority of healthy human infants. The exact mechanism of asymptomatic colonisation is unclear; however, previous studies in this laboratory have shown that components of both the immunoglobulin and non-immunoglobulin fractions of human milk bind to toxin A and prevent its interaction with hamster intestinal brush border membranes (BBMs). Secretory IgA (sIgA) is the primary immunoglobulin found in human milk. As sIgA resists digestion in the infant stomach and passes at high levels into the colon, its ability to bind toxin A was the subject of this investigation. Purified sIgA in concentrations at and below those found in human milk inhibited the binding of toxin A to purified BBM receptors. Heating sIgA to 100° for 5 min did not affect its inhibitory activity. IgM, IgG and serum IgA did not appreciably inhibit the binding of toxin A to BBM receptors. SDS-PAGE separated sIgA into three major bands: secretory component, heavy chains and light chains. Autoradiography with radiolabelled toxin A revealed that toxin A bound to the secretory component (SC) of sIgA. When the three purified subunits of sIgA were coated on to microtitration wells, SC bound significantly more toxin A than the heavy or light chains of sIgA. Purified SC also inhibited toxin binding to receptors in a dose-dependent fashion similar to sIgA. The heavy and light chains of sIgA did not inhibit toxin A receptor binding. Removing carbohydrates from sIgA and SC by enzymic digestion showed that toxin A binds much less to deglycosylated SC than to glycosylated SC. These data suggest that SC in human milk binds to toxin A and may function as a receptor analogue, protecting human infants against C. difficile -associated disease.