Abstract
It was shown previously that the development of a primary immune response in vitro in the Mishell-Dutton system was strongly inhibited by increased cell densities (Gurvich et al., Immunology 1975. 28: 271). In the present work, the rate of onset of this inhibition was studied in C57BL/6 mouse spleen cell suspensions during the phase of exponential increase of antibody-forming cells (AFC) after 3 days' cultivation in vitro with the antigen. It has been shown that the increase in AFC number is very soon inhibited following an increase in the cellular density, the inhibition already being evident within 2 or 4 h. Parallel reduction in incorporation of radioactive precursors in DNA and especially RNA is observed, whereas inhibition of protein synthesis was delayed.