Influence of hydroxyurea on lectin-induced early and late events in peripheral blood lymphocyte cultures

Activation events induced by lectins in human lymphocyte cultures differed not only in time kinetics of their appearance but were also in a different manner inhibited by hydroxyurea (HU). 4F2 and Tac expression, thermostable sheep erythrocyte rosette formation, cell volume distribution changes and the enhancement of the purine metabolic rate [( 3H]adenine incorporation) induced by PHA, Con A or PWM were not influenced by HU treatment, suggesting G1-phase dependency of these markers. The decrease in the mitogen-induced marker expression after 48 h of incubation with HU can be explained by the unability of activated cells to process the cell cycle, to divide and to become newly positive cells. Mitogen-induced RNA synthesis was partially, DNA synthesis, PWM-induced Ig synthesis and lectin-mediated HLA class II antigen expression were totally inhibited by HU. It holds especially for the DR antigen that its appearance in a polyclonal model of lymphocyte activation occurs in a later (postmitotic G1) phase of the cell cycle. The inhibitory effect of HU on late activation parameters could be removed after washing the cells. Mitogen-activated, HU-treated PBL cultures after removing HU continued cell cycle progression without requirement for further addition of lectin.