Dendritic cell appearance and differentiation during early and late stages of rat stomach
carcinogenesis were studied in the pyloric mucosa. Young male rats were given
drinking water with or without
N-methyl-N'-nitro-N-nitrosoguanidine (
MNNG; 100 mg/liter) for 14 days. Use of competitive RT-PCR and northern blotting showed that
MNNG exposure induced 3- to 4-fold greater expression of the genes for
integrin beta7 and
integrin alphaE2 (identical with
antigen OX-62, a dendritic cell marker), as well as three
cytokines,
IL-4,
GM-CSF and
TNFalpha, in the stomach pyloric mucosa of resistant Buffalo rats compared to sensitive ACI rats. These genes were minimally expressed in control animals. The results confirm the appearance of dendritic cells in the target pyloric mucosa and suggest the possibility that dendritic cell differentiation and maturation are induced by various
cytokines, at least in Buffalo rats. Competitive RT-PCR showed expression of
integrin alphaE2 and beta7, MHC
class II-associated invariant chain (Ii), MHC class II, B7-1, CD28,
GM-CSF and
TNFalpha genes in all 12 examined stomach
adenocarcinomas and
adenomas induced in male Lewis and WKY rats with 30 weeks'
MNNG exposure, suggesting the presence of dendritic cells in
tumors. OX-62 staining and western blotting for OX-62 also confirmed the presence of dendritic cells in
tumors. However, the population of dendritic cells in
tumors was less than that in the pyloric mucosa after 14 days'
MNNG exposure. The present results suggest that immune defense involving dendritic cells is marshaled from the very early initiation stage during rat
stomach cancer development, but is downgraded in developed
tumors.