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Methionine Overcomes Neural Tube Defects in Rat Embryos Cultured on Sera from Laminin-Immunized Monkeys^1,2,

Center for Environmental Health, Department of Animal Science ^* Electron Microscopy Laboratory, Department of Physiology and Neurobiology, University of Connecticut, Storrs, CT 06269

Sera from laminin-immunized monkeys were previously found to cause neural tube defects in cultures of whole rat embryos by unknown mechanisms. In the present study, adding L-methionine to either the culture media or to the diets of the monkeys overcame the toxicity of the serum from one of these monkeys (LAM3) but not the other (LAM4). The antilaminin antibody levels and avidities for isolated murine laminin of sera from the two monkeys were comparable. However, when yolk sac homogenates were tested on ELISA, antibodies from LAM4 had greater binding than LAM3, which was further supported by immunoelectron microscopy. These differences in antibody binding were explained by the findings that antibodies from LAM4 recognized more epitopes than LAM3 and that LAM4 recognized specific epitopes not recognized by LAM3. These antibodies caused reductions in the number of microvilli on the cells and the cell sizes of the yolk sac endoderm. In addition, uptake of [¹⁴C]methionine, [¹⁴C]sucrose and [¹⁴C]valine by yolk sacs from embryos cultured on serum from LAM4 was less than that for LAM3. We suggest that the neural tube defects caused by the antilaminin antibodies were a result of reduced nutrient flow caused by the reduction in the number of microvilli on the cells of the yolk sac endoderm.

KEY WORDS: • laminin • methionine • monkeys • folic acid • autoimmunity

¹ Supported by NIEHS grant ESO4312 (N. Klein); scientific contribution 1570 from the Storrs Agricultural Experiment Station.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

³ Current address: Karolinska Institute, Box 280, 17177, Stockholm, Sweden.

⁴ To whom correspondence should be addressed.

Manuscript received 29 July 1994. Revision accepted 21 November 1994.