Cross-reactivity of rat, mouse, and human IgD

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.