B-B cell interaction involved in polyclonal B cell activation is restricted by I-A but not by I-E molecules

We have previously demonstrated that the class II MHC restricted B-B cell interaction is involved in the polyclonal differentiation of unprimed murine B cells into IgM-producing cells induced by a T cell-derived lymphokine B151-TRF2 or bacterial LPS. The present study has addressed the question of whether I-A and/or I-E molecules function as restriction elements for the B-B cell interaction. The results revealed that (B10 x B10.BR)F1(H-2b/k) B cells could be separated into I-Ab- and 1-Ak-restricted subpopulations by their ability to bind to B10(H-2b) or B10.BR(H-2k) B cell monolayers, whereas an I-E-restricted F1 B cell population was not obtained. Moreover, B10-derived B cells isolated from (B10 + B10.BR) - (B10 x B10.BR)F1 but not from B10 - (B10 x B10.BR)F1 radiation-induced bone marrow chimeras acquired newly the ability to co-operate with mitomycin C-treated auxilary B cells expressing I-Ak but not I-Ek molecules. Thus, these results indicate that I-E molecules, unlike I-A molecules, do not serve as restriction elements for the B-B cell interaction, and that I-A and I-E molecules on B cells play functionally disparate roles in the activation of polyclonal B cells.