Sprague-Dawley rats were infected with Nippostrongylus brasiliensis larvae, and IgE formation was studied. Before infection, the serum IgE level was less than 0.4 μg/ml. The IgE level began to increase from the 10th day of infection, reached its maximum (50-100 μg/ml) at the 14th day and gradually declined. Reinfection of the rats resulted in an increase of the serum IgE level within 7 days. The IgE antibody response to N. brasiliensis antigens did not parallel the increase of IgE synthesis. In most animals, the antibody became detectable in the serum at the 21st day when the total IgE level already began to decrease. The animals showed a secondary IgE antibody response upon reinfection. Both mesenteric lymph nodes and spleen cell suspensions were examined for the presence of IgE-bearing cells (IgE-B cells) and IgE-forming cells by fluorescent antibody technique. The IgE-bearing lymphocytes became detectable in the mesenteric lymph nodes and spleen at the 8th day of infection. The proportion of the IgE-B cells in nonadherent cell population gradually increased and reached maximum at the 14th day; about 20% of immunoglobulin (Ig)-bearing cells in the mesenteric lymph nodes and 10% of Ig-bearing cells in spleen bore IgE on their surface. Evidence was obtained that these lymphocytes synthesized IgE. The IgE-forming cells were detected in both mesenteric lymph nodes and spleen of the infected animals. The number of IgE-forming cells was greater in the mesenteric lymph nodes than in spleen, indicating that the regional lymph nodes are the major source of serum IgE in the N. brasiliensis-infected animals.
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