PHOSPHODIESTERASE PROFILE OF HUMAN B-LYMPHOCYTES FROM NORMAL AND ATOPIC DONORS AND THE EFFECTS OF PDE INHIBITION ON B-CELL PROLIFERATION

1 CD19(+) B lymphocytes were purified from the peripheral blood of nor mal and atopic subjects to analyse and compare the phosphodiesterase ( PDE) activity profile, PDE mRNA expression and the importance of PDE a ctivity for the regulation of B cell function. 2 The majority of cycli c AMP hydrolyzing activity of human B cells was cytosolic PDE4, follow ed by cytosolic PDE7-like activity; marginal PDE3 activity was found o nly in the particulate B cell fraction. PDE1, PDE2 and PDE5 activities were not detected. 3 By cDNA-PCR analysis mRNA of the PDE4 subtypes A , B (splice variant PDE4B2) and D were detected. In addition, a weak s ignal for PDE3A was found. 4 No differences in PDE activities or mRNA expression of PDE subtypes were found in B cells from either normal or atopic subjects. 5 Stimulation of B lymphocytes with the polyclonal s timulus liyopolysaccharide (LPS) induced a proliferative response in a time-and concentration-dependent manner, which was increased in the p resence of interleukin-4 (IL-4). PDE4 inhibitors (rolipram, piclamilas t) led to an increase in the cellular cyclic PIMP concentration and to an augmentation of proliferation, whereas a PDE3 inhibitor (motapizon e) was ineffective, which is in accordance with the PDE profile found. The proliferation enhancing effect of the PDE4 inhibitors was partly mimicked by the cyclic BMP analogues dibutyryl (db) cyclic AR?IP and o -1-beta-D-ribofuranosylbenzimidazole-3',5'-cyclic monophosphorothioate , Sp-isomer (dcl-cBIMPS), respectively. However, at concentrations exc eeding 100 mu M db-cyclic AMP suppressed B lymphocyte proliferation, p robably as a result of cytotoxicity. Prostaglandin E-2 (PGE(2), 1 mu M ) and forskolin (10 mu M) did not affect B cell proliferation, even wh en given in combination with rolipram. 6 Inhibition of protein kinase A (PKA) by differentially acting selective inhibitors (KT 5720, Rp-8-B r-cyclic AMPS) decreased the proliferative response of control cells a nd reversed the proliferation enhancing effects of rolipram. 7 Importa ntly, PDE4 activity in LPS/IL-4-activated B lymphocytes decreased by a bout 50% compared to unstimulated control values. 8 We conclude that a n increase in cyclic AMP, mediated by down-regulation of PDE4 activity , is involved in the stimulation of B cell proliferation in response t o LPS/IL-4. B cell proliferation in response to a mitogenic stimulus c an be further enhanced by pharmacological elevation of cyclic AMP.