An unbiased stereological study on subpopulations of rat liver macrophages and on their numerical relation with the hepatocytes and stellate cells.

Studies on liver macrophages have elucidated their key roles in immunological, fibrotic and regenerative responses, and shown that macrophages are not a homogeneous population. In the rat, two sets of liver macrophages coexist, identified by ED1 and ED2 antibodies. Those sets have different quantitative responses in liver injuries and may have different tasks throughout the injury and recovery phases. Nevertheless, the total number (N), number per gram (N g(-1)) and proportion of those macrophages in relation to other liver cells has never been quantified using design-based stereology. Thus, we combined immunocytochemistry with those tools to produce an unbiased estimate of the N of ED1(+) and of ED2(+) cells. A smooth fractionator sampling scheme was applied to the liver of five male Wistar rats (3 months old), to obtain systematic uniform random sections (30 microm thick); these were immunostained with the monoclonal antibodies: ED1, a pan-macrophagic marker; and ED2, which identifies the completely differentiated macrophages, i.e. Kupffer cells. The N of ED1(+) cells was 340 x 10(6), estimated with a coefficient of error (CE) of 0.04, and that of ED2(+) cells was 283 x 10(6), with a CE of 0.05. These figures correspond to 10.7% and 8.9%, respectively, of the total liver cells. The new data constitute reference values for correlative inferences. Also, the methodological strategy, by its accuracy and precision, is valuable for future investigations on the liver cell composition in various models of disease, and especially for studying the more subtle variations that occur during the injury and recovery phases.