No abstract

Mutatect MN-11 is a tumor line that can be grown subcutaneously in syngeneic C57BL/6 mice. The frequency of spontaneously arising mutants at the hypoxanthine phosphoribosyltransferase (Hprt) locus was observed to be elevated as a result of in vivo growth. The objective of the present study was to identify factors in the tumor microenvironment that might explain this increase in mutant frequency (MF). When tumors were examined histologically, neutrophils were found to be the predominant infiltrating cell type. Quantitative estimates of the number of neutrophils and MF of tumors in different animals revealed a statistically significant correlation (r ‫؍‬ 0.63, P < 0.0001). Immunohistochemical analysis for inducible nitric oxide synthase (iNOS) demonstrated its presence, mainly in neutrophils. Biochemical analysis of tumor homogenates for nitric oxide synthase (NOS) activity indicated a statistically significant correlation with MF (r ‫؍‬ 0.77, P < 0.0001). Nitrotyrosine was detected throughout the tumor immunohistochemically; both cytoplasmic and nuclear staining was seen. To increase the number of infiltrating neutrophils, tumors were injected with chemoattractant interleukin-8 and prostaglandin E2. This produced a statistically significant increase in neutrophil content (P ‫؍‬ 0.005) and MF (P ‫؍‬ 0.0002). As in control MN-11 tumors, neutrophil content and MF were strongly correlated (r ‫؍‬ 0.63, P ‫؍‬ 0.003). Because neutrophils are a potential source of genotoxic reactive oxygen and/or nitrogen species, our results support the notion that these tumor-infiltrating cells may be mutagenic and contribute to the burden of genetic abnormalities associated with tumor progression.

We investigated the pathogenesis of soft-tissue contracture in club foot, using immunohistochemistry to study 41 biopsy specimens and 12 normal deltoid ligaments from cadavers. Five biopsy specimens were studied by electron microscopy (EM) to determine the presence of myofibroblasts. All 41 specimens of club foot stained positively for vimentin as against only one of the 12 control specimens. By contrast, there was no difference in staining for desmin or alpha-smooth muscle actin. EM showed some variability in the appearance of ligamentous cells. Most contained bundles of microfilaments in the cytoplasm and many had abundant pinocytotic vesicles, but no basal lamina or plasmalemmal attachment plaques. Cells of the medial ligamentous tissue in patients with club foot contain vimentin and others have myofibroblastic characteristics. Both features may contribute to recurrence after soft-tissue release.