Highly purified sheep anti-rat lymphocyte membrane IgD (mIgD) was used to detect cross-reactivity with the putative murine-δ chain on mouse lymphocytes. Cross-reactivity is demonstrated by indirect immunofluorescent staining and by immunoprecipitation of 125I-labeled lymphocyte membrane extracts followed by electrophoresis on 10% polyacrylamide gels. In addition, cross-reactivity of anti-rat-δ with human IgD is shown by gel diffusion analysis.

The anti-rat-δ reagent stained both Ig5a+ and Ig5b+ lymphocytes. Preincubation of Ig5b+ (but not Ig5a+) cells with monoclonal allotype-specific antibodies (anti-Ig5b) under capping conditions caused inhibition of staining by the sheep anti-rat-δ reagent, indicating that it is the δ-chain that is recognized on mouse lymphocytes and that the anti-rat-δ reagent does not distinguish between mouse-δ allotypes. Furthermore, absorption of the sheep anti-rat-δ serum with purified human IgD reduced subsequent staining of mouse lymphocytes by approximately 50%; staining was not affected by absorption with human IgM. This xenogeneic anti-δ antiserum appears to detect determinants on the δ-heavy chain, which are shared by at least three species of mammals, suggesting that these determinants represent important molecular features conserved during evolution.

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This work was supported by Grants HD12381, CA24031, and AI14985 from the United States Public Health Service, National Science Foundation Grant 06949, and grants from the American Cancer Society and the National Foundation March of Dimes.

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