The immune response in stationary suspension cultures containing different numbers of cells. The surface density effect.

Correlation between the number of dissociated spleen cells, incubated with antigen in a modified Mishell and Dutton system, and the number of antibody-forming cells (AFC) produced as a result of incubation has been studies in mice of C57Bl/6 strain. It has been shown that when suspension densities are increased 2- to 4-fold, the number of AFC formed is very often reduced 10- to 100-fold, although the percentage of viable cells recovered at the end of incubation is not significantly diminished. The observed reduction of AFC formation in cultures containing increased numbers of cells, designated here the surface density effect, was found to be expressed more by spleen cells of unimmunized than of immunized mice. Inhibition was dependent on the thickness of the cell layer formed on the bottom of the incubation vessel (cells per square centimeter), rather than on the cell: volume ratio of cultures. The effect was not due to a deficit of antigen or nutrition and could not be reproduced by adding of incubation media conditioned by dense cultures. It was determined not by impairment of clone induction but by inhibition of subsequent proliferation. This suppression is reversible and can be reversed by decreasing the cell density, even after 3 days of culture.