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The Immune Response to Dextran in BALB/c Mice

I. Modification of "Thymus-Independent" Response by the T Cell Mitogen Concanavalin A¹

From the Department of Immunology and Microbiology, Wayne State University School of Medicine, Detroit, Michigan 48201

Abstract

Normal and congenitally athymic mice respond to immunization with dextran, thus indicating that the response is thymus independent. Athymic mice have lower plaque-forming cell (PFC) response than normal mice 3 days after immunization, but similar PFC response as normal mice by 5 days. Seven to 10 days after immunization, athymic mice maintain a high level of PFC response whereas the PFC response declines sharply in normal mice.

Concanavalin A (Con A), added at initiation of in vitro culture, enhances the response of spleen cells from primed normal mice. Treatment with methyl--D-mannoside (MAM), a competitive inhibitor of binding of Con A, immediately after addition of Con A, abolishes the enhancement. Treatment with MAM, 3 to 6 hr after Con A addition, partially blocks the enhancement. The enhancing effect is dependent on the dose of Con A and the duration of in vivo priming before in vitro culture.

Con A does not enhance the in vitro PFC response of cells from primed athymic mice. Supernatants from Con A-treated non-primed normal spleen cell cultures enhance the PFC response of "nude" cells, thereby indicating that enhancement by Con A is mediated through a soluble T cell product(s) with no apparent antigen specificity.

Hydroxyurea, an inhibitor of DNA synthesis, blocks the enhancement by Con A of cells primed for 1 to 3 days. Release of hydroxyurea block after 19 hr incubation does not restore the PFC response, thereby indicating the responding anti-dextran PFC precursor cells are engaging actively in DNA synthesis. PFC response of primed cells taken at the peak of anti-dextran response (day 5) shows that they are less susceptible to the hydroxyurea block. Con A enhances the PFC response of cells primed for 5 days even in the absence of DNA synthesis.

Footnotes

¹ This work was supported by U.S. Public Health Service Grant AI-10724 from the Institute of Allergy and Infectious Diseases.