In this study, the pitfalls of tumor measurement in the nude mouse were evaluated. Regarding intermethod variation, diameters of subcutaneous tumors in nude mice were expressed as length, area, and volume; tumor weights were also recorded. These measurements were all compared to a reference standard: water displacement volume. Estimates of area and volume derived from caliper measurements correlated well with water displacement volume (r = 0.97 and 0.98, respectively). At necropsy, tumor weight was the most consistent and reproducible reflection of tumor volume (r = 1.0000). Regarding interobserver variation, mean absolute difference among volumes determined by several investigators who measured the same tumors in living animals was determined. This averaged 15% of the mean calculated volume. Regarding intraobserver variation, observers measured four separate masses in nude mice eight times each. The observers were prevented from realizing that the same animals were being repeatedly evaluated. Volumes were compared in order to quantify the average variation that occurs when a single investigator repeatedly measures the same mass. When large masses were measured, this error was 7%; when small masses were measured, the error was 27%. Recommendations are made for future work employing tumor measurement.

Circulating murine monocytes comprise two largely exclusive subpopulations that are responsible for seeding normal tissues (Gr-1−/CCR2−/CX3CR1high) or responding to sites of inflammation (Gr-1+/CCR2+/CX3CR1lo). Gr-1+ monocytes are recruited to the site of infection during the early stages of immune response to the intracellular pathogen Toxoplasma gondii. A murine model of toxoplasmosis was thus used to examine the importance of Gr-1+ monocytes in the control of disseminated parasitic infection in vivo. The recruitment of Gr-1+ monocytes was intimately associated with the ability to suppress early parasite replication at the site of inoculation. Infection of CCR2−/− and MCP-1−/− mice with typically nonlethal, low doses of T. gondii resulted in the abrogated recruitment of Gr-1+ monocytes. The failure to recruit Gr-1+ monocytes resulted in greatly enhanced mortality despite the induction of normal Th1 cell responses leading to high levels of IL-12, TNF-α, and IFN-γ. The profound susceptibility of CCR2−/− mice establishes Gr-1+ monocytes as necessary effector cells in the resistance to acute toxoplasmosis and suggests that the CCR2-dependent recruitment of Gr-1+ monocytes may be an important general mechanism for resistance to intracellular pathogens.

Lung cancer, primarily associated with tobacco use, is the leading cause of cancer morbidity and mortality in the United States. Squamous cell carcinoma (SCC) is one of the four major histological types of lung cancer. Although there are several established models for lung adenoma and adenocarcinomas, there is no well-established mouse model for lung SCC. We treated eight different inbred strains of mice with N-nitroso-trischloroethylurea by skin painting and found that this regimen induced lung SCCs in five strains of mouse (SWR/J, NIH Swiss, A/J, BALB/cJ, and FVB/J) but not in the others (AKR/J, 129/svJ, and C57BL/6J). Mouse lung SCCs have similar histopathological features and keratin staining to human SCC. Moreover, a wide spectrum of abnormal lung squamous phenotypes including hyperplasia, metaplasia, carcinoma in situ, and invasive carcinoma, were observed. There are strain-specific differences in susceptibility to Lscc induction by N-nitroso-tris-chloroethylurea with NIH Swiss, A/J, and SWR/J mice developing scores of SCCs whereas the resistant strains AKR/J, 129/svJ, and C57BL/6J failed to develop any SCCs. FVB/J and BALB/cJ mice had an intermediate response. We conducted whole-genome linkage disequilibrium analysis in seven strains of mice, divided into three phenotype categories of susceptibility, using Fisher's exact test applied to 6,128 markers in publically available databases. Three markers were found significantly associated with susceptibility to SCC with the P < 0.05. They were D1Mit169, D3Mit178, and D18Mit91. Interestingly, none of these sites overlap with the major susceptibility loci associated with lung adenoma/adenocarcinoma development in mice. The mouse SCC described here is highly significant for preclinical studies of lung cancer chemopreventive agents because most human trials have been conducted against precancerous lesions for SCC. Furthermore, this model can be used in determining genetic modifiers that contribute to susceptibility or resistance to lung SCC development.

Extrahepatic biliary atresia (BA) is a devastating disease of the neonate in which the hepatic and/or common bile duct is obliterated or interrupted. Infants and children with this diagnosis constitute 50% to 60% of the pediatric population that undergoes orthotopic liver transplantation. However, there is still very little known about the etiology and pathogenesis of BA. Several recent studies have demonstrated that anomalies of situs determination are more commonly associated with BA than previously recognized. In this study, we examined the pathogenesis of jaundice in the inv mouse, a transgenic mouse in which a recessive deletion of the inversin gene results in situs inversus and jaundice. The results show that these mice have cholestasis with conjugated hyperbilirubinemia, failure to excrete technetium-labeled mebrofenin from the liver into the small intestine, lack of continuity between the extrahepatic biliary tree and the small intestine as demonstrated by Trypan blue cholangiography, and a liver histological picture indicative of extrahepatic biliary obstruction with negligible inflammation/necrosis within the hepatic parenchyma. Lectin histochemical staining of biliary epithelial cells in serial sections suggests the presence of several different anomalies in the architecture of the extrahepatic biliary system. These results suggest that the inversin gene plays an essential role in the morphogenesis of the hepatobiliary system and raise the possibility that alterations in the human orthologue of inversin account for some of the cases of BA in which there are also anomalies of situs determination. (HEPATOLOGY 1999;30:372-378.)