Fig. 1.

Probabilistic regulation of time to die. Small resting B cells from spleens or lymph nodes were placed in culture under different conditions, and survival was measured by propidium iodide uptake. Cell numbers were counted by reference to beads as described (7). Fitting was performed by using a Matlab fmincon function. (A) Survival curves were fitted by using an exponential decay function [solid line, k = 0.35, 95% confidence interval (C.I.) (+0.011, −0.008)] or a lognormal survival function without T = 0 and T = 1 [dashed line, μ = 48.55, 95% C.I. (+2.3, 2.2), σ = 24.90, 95% C.I. (+4.6, −4.5)]. (B) Survival of B cells isolated from lymph nodes by using the quick preparation method. Data fitted using lognormal survival function [dashed line, μ = 42.59, 95% C.I. (+4.6,−4.5), σ = 29.08, 95% C.I. (+3.8, −3.0)]. The probability distribution function of the fitted lognormal is represented in Inset. (C) Survival curves of B cells isolated from spleen and cultured either alone [circles, μ = 45.40, 95% C.I. (+1.8, −1.7), σ = 36.94, 95% C.I. (+7.3, −5.9)] or with saturating IL-4 [squares, μ = 62.33, 95% C.I.(+2.2, −2.0), σ = 30.02, 95% C.I. (+5.1, −4.2)]. (D) The values for μ and σ of lognormal survival function fit to viability data for three experiments titrating IL-4. Error bars for A–C represent SEM for triplicate samples. Error bars in D represent 95% C.I.s assigned by using a Monte Carlo simulation.