Age-related changes in dermal mast cell prevalence in BALB/c mice: functional importance and correlation with dermal mast cell expression of Kit.

Differences in dermal mast cell prevalence for adult mice of different strains have been reported previously. In this study, the dermal mast cell prevalence for BALB/c and C57BL/6 mice at 6 weeks of age was similar but as BALB/c mice matured from 6 to 10 weeks of age, their dermal mast cell prevalence halved. In contrast, there was no significant difference in the dermal mast cell prevalence of 6- and 10-week-old C57BL/6 mice. These differences determined the degree of susceptibility of BALB/c and C57BL/6 mice of different ages to UVB (UV radiation of wavelength 280-320 nm)-induced systemic immunosuppression. Expression of the receptor for stem cell factor, Kit protein, was examined on mast cells under conditions in which the dermal mast cell prevalence varied. A significant correlation was observed between Kit expression by mast cells from adult BALB/c, DBA/2 and C57BL/6 mice and dermal mast cell prevalence. In BALB/c mice, mast cell Kit expression decreased as the mice matured from 6 to 10 weeks of age and correlated with the reduction in dermal mast cell numbers. Kit levels on dermal mast cells from C57BL/6 mice were consistently higher than on mast cells from BALB/c mice although significant reductions in Kit were also measured with ageing from 6 to 10 weeks. We hypothesize that regardless of the extent of Kit expression, the dermal mast cell populations were maximally expanded in C57BL/6 mice. We suggest that BALB/c mice of 6 and 10 weeks of age are useful hosts in which to quantitatively evaluate mast cell involvement in a range of functional assays involving skin.