T-cell-dependent B-cell stimulation is H-2 restricted and antigen dependent only at the resting B-cell level.

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Abstract
Cloned lines of helper thymus-derived (T) cells produce help for bone marrow-derived (B) cell growth and Ig [immunoglobulin] secretion in the presence of histocompatible adherent cells and of specific antigen. This help stimulates histocompatible and histoincompatible B cell blasts polyclonally. Neither antigen nor histocompatibility, but antigen-unspecific factor(s) for growth and Ig secretion are required to stimulate a B cell blast through the next round of division. Only histocompatible, resting, small B cells and only those binding their specific antigen can be stimulated by antigen-activated T cell help to initiate growth and Ig secretion. The preference of the resting B cells for such collaboration with T cell help is mapped to the K end of the H-2 histocompatibility locus and probably constitutes the antigen expressed on B cells by the immune response (I) region. A resting B cell is apparently excited by the binding of specific antigen to surface Ig and by the interaction of its surface Ia antigen with helper T cells. After this dual recognition, the excited B cell can be stimulated by the antigen-unspecific factor(s) generated by the interaction of helper T cells, adherent cells and antigen to initiate replication.