Comparative analysis of dendritic cell density and total number in commonly transplanted organs: morphometric estimation in normal mice.

Dendritic cells (DC) are considered to be the major cell type responsible for induction of primary immune responses. While they have been shown to play a critical role in eliciting allosensitization via the direct pathway, there is evidence that maturational and/or activational heterogeneity between DC in different donor organs may be crucial to allograft outcome. Despite such an important perceived role for DC, no accurate estimates of their number in commonly transplanted organs have been reported. Therefore, leukocytes and DC were visualized and enumerated in cryostat sections of normal mouse (C57BL/10, B10.BR, C3H) liver, heart, kidney and pancreas by immunohistochemistry (CD45 and MHC class II staining, respectively). Total immunopositive cell number and MHC class II+ cell density (C57BL/10 mice only) were estimated using established morphometric techniques--the fractionator and disector principles, respectively. Liver contained considerably more leukocytes (approximately 5-20 x 10(6)) and DC (approximately 1-3 x 10(6)) than the other organs examined (pancreas: approximately 0.6 x 10(6) and approximately 0.35 x 10(6); heart: approximately 0.8 x 10(6) and approximately 0.4 x 10(6); kidney approximately 1.2 x 10(6) and 0.65 x 10(6), respectively). In liver, DC comprised a lower proportion of all leukocytes (approximately 15-25%) than in the other parenchymal organs examined (approximately 40-60%). Comparatively, DC density in C57BL/10 mice was heart > kidney > pancreas >> liver (approximately 6.6 x 10(6), 5 x 10(6), 4.5 x 10(6) and 1.1 x 10(6) cells/cm3, respectively). When compared to previously published data on allograft survival, the results indicate that the absolute number of MHC class II+ DC present in a donor organ is a poor predictor of graft outcome. Survival of solid organ allografts is more closely related to the density of the donor DC network within the graft.