Figure 1.

Immature B cells accumulate in mice lacking both Ii and MHC class II β-chain. (A) Cytofluorimetric analysis of CD23 and IgM on B220⁺ cells. Control, Ii^−/−, and double-deficient (double^−/−) splenocytes were stained with both antibody to B220 (anti-B220) and anti-IgM or anti-CD23. Histograms show the expression of these molecules on B220 cells. (B) IgM response to TI antigen. Control, Ii^−/−, and double-deficient (double^−/−) mice were challenged with the type II-TI antigen NP₉₀-Ficoll. Six days after injection, blood was drawn and IgM titers were quantitated by ELISA. The graph shows concentration of antibodies at days 0 and 6 from four control, Ii^−/−, and double ^−/− mice. The results presented are the average of four injected mice.