tokens: From this and other findings the picture emerges that there are at least three categories of factors which mediate cell-type-specific transcription in B lymphocytes : ( a ) cell-specific factors such as Oct-2A and Oct-2B that are not expressed in most other cell types : ( b ) ubiquitous factors such as NF-kappa B that are constitutively active in B cells but are sequestered in an inactive form in other cells ; ( c ) ubiquitously active factors , exemplified by the one binding to the E3 sequence motif .