Phenotypic analysis of immunocompetent cells in healthy human dental pulp

Like other tissues in the body, the human dental pulp is equipped with a network of immune cells that can be mobilized against pathogens when they invade the tooth. Very little data, mostly obtained with classic histologic methods, have reported their quantities and relative percentages. The objective of this study was to characterize and precisely quantify immunocompetent cells in healthy human dental pulp by using fluorescence-activated cell sorting, together with identifying specific cell subsets in the leukocyte (CD45(+)) cells.

Healthy human third molars were collected from 42 young patients. Dental pulps were separated from the hard tissues and prepared for flow cytometry or immunostaining analyses.

CD45(+) cells represented 0.94% ± 0.65% of cells obtained from the enzymatic digestion of whole dental pulps (n = 34). CD16(+)CD14(+) granulocytes/neutrophils (50.01% ± 9.08%, n = 7) were found to represent the major subpopulation in CD45(+) cells followed by CD3(+) T lymphocytes (32.58% ± 11%, n = 17), CD14(+) monocytes (8.93% ± 5.8%, n = 7), and HLA-DR(high) Lin1(-) dendritic cells (4.51% ± 1.12%, n = 7). Minor subpopulations included CD3(-)CD56(+) natural killer cells (2.63% ± 1.15%, n = 7) and CD19(+) B lymphocytes (1.65% ± 0.89%, n = 17). We further identified cells harboring a phenotype compatible with Foxp3/CD25-expressing regulatory T lymphocytes (CD45(+)CD3(+)CD4(+)CD127(low)). Fluorescence-activated cell sorting analysis and confocal microscopy also revealed expression of HO-1 in HLA-DR(+) cells.

For the first time, this study identifies and precisely quantifies the relative proportion of immunocompetent cells potentially involved in tissue homeostasis of healthy human dental pulp.