Image analysis of cell proliferation and differentiation in the thymus of the newtPleurodeles waltlii Michah. by SAMBA 200 cell image processing.

The relationships between cell kinetics and nuclear transformations related to cell differentiation were investigated in the thymus of the newt by means of image analysis. A SAMBA 200 cell image processor was used to compute 18 densitometric, textural and morphological parameters on Feulgen-stained thymic nuclei from a few days after hatching of larvae (stage 40) to 1 month after metamorphosis (150 days old). During the first step, cell nuclei were automatically identified as lymphoid or epithelial with a 93.4%-98.7% confidence level when compared with the cytological diagnoses. During the second step, four cell classes were recognized in both epithelial and lymphoid cell populations and assumed to correspond toG 0,G 1,S andG 2 cell subpopulations, on the basis of both the nuclear DNA content and the chromatin pattern. The variations in the percentages of cells in these four classes, in addition to the evolution of growth fraction and cell number, indicate that the thymus is basically an exponentially growing epithelial bud, which reaches a steady state during metamorphosis. A few lymphoidG 0 stem cells penetrate the epithelial bud up to stage 42, enter theG 1 phase of the mitotic cycle, and give rise to lymphoblasts. Then, lymphoblast cells produce lymphocytes, which perform intensive proliferation until metamorphosis, while an increasing proportion of them leave the thymus. During metamorphosis, a steady state is reached in the lymphoid cell population as in the epithelial one, and statistically half the number of new lymphocytes emigrate.