Low-dose exposure and immunogenicity of transgenic maize expressing the Escherichia coli heat-labile toxin B subunit.
BACKGROUND
Transgenic maize, which produces the nontoxic B subunit of the Escherichia coli heat-labile toxin (LT-B) in seed, has proven to be an effective oral immunogen in mice. Currently, there is considerable concern over accidental consumption of transgenic maize expressing LT-B by humans and domestic animals. We have yet to define nonimmunogenic levels of transgenic LT-B when ingested.


OBJECTIVE
Our goal in this study was to determine the highest dose of LT-B orally administered in mice that does not result in a measurable immune response. We defined an immune response as specific serum or mucosal IgG or IgA significantly greater than background after three feedings (0.0002-20 mug) or a priming response induced by the intermittent feeding.


METHODS
We fed transgenic maize pellets on days 0, 7, 21, and 49 and collected serum and fecal samples weekly. Serum was analyzed for LT-B-specific IgG and IgA, and feces was analyzed for LT-B-specific IgA.


RESULTS
We observed a dose-dependent anti-LT-B antibody response with high specific antibody concentrations in groups fed high doses (0.2, 2, 20 mug) of LT-B maize. Mice fed 0.02 mug LT-B demonstrated immune priming in 62.5% of the animals. Mice that were fed </= 0.002 mug LT-B showed no increase in specific antibody nor did they demonstrate immune priming, indicating that 0.002 mug LT-B was the highest nonimmunogenic dose tested.


CONCLUSIONS
Our results demonstrate that LT-B derived from transgenic maize is immunogenic at nanogram levels when orally administered to mice.
Beyer
April J
AJ
Interdepartmental Microbiology, Iowa State University, Ames, Iowa 50011, USA.
Wang
Kan
K
Umble
Amber N
AN
Wolt
Jeffrey D
JD
Cunnick
Joan E
JE
D000818:Animals; D001427:Bacterial Toxins / Q000235:genetics / Q000276:immunology*; D001992:Bronchoalveolar Lavage Fluid / Q000276:immunology; D004768:Enterotoxins / Q000235:genetics / Q000276:immunology*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000276:immunology*; D005243:Feces / Q000737:chemistry; D005260:Female; D007070:Immunoglobulin A / Q000097:blood / Q000276:immunology; D007074:Immunoglobulin G / Q000097:blood / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D030821:Plants, Genetically Modified / Q000276:immunology*; D003313:Zea mays / Q000235:genetics* / Q000276:immunology
D001427:Bacterial Toxins; D004768:Enterotoxins; D029968:Escherichia coli Proteins; D007070:Immunoglobulin A; D007074:Immunoglobulin G; C027538:heat-labile enterotoxin, E coli