Mouse embryonic fibroblast (MEF) cells are commonly used as feeder cells to maintain the pluripotent state of stem cells. MEFs produce growth factors and provide adhesion molecules and extracellular matrix (ECM) compounds for cellular binding. In the present study, we compared the expression levels of Fgf2, Bmp4, ActivinA, Lif and Tgfb1 genes at the mRNA level and the level of Fgf2 protein secretion and Lif cytokine secretion at passages one, three and five of MEFs isolated from 13.5-day-old and 15.5-day-old embryos of NMRI and C57BL/6 mice using real-time PCR and enzyme-linked immunosorbent assay. We observed differences in the expression levels of the studied genes and secretion of the two growth factors in the three passages of MEFs isolated from 13.5-day-old and 15.5-day-old embryos, respectively. These differences were also observed between the NMRI and C57BL/6 strains. The results of this study suggested that researchers should use mice embryos that have different genetic backgrounds and ages, in addition to different MEF passages, when producing MEFs based on the application and type of their study.

The survival, growth and development of Onchocerca lienalis 3rd-stage (L3) larvae implanted into mice within micropore chambers has been studied with a view to developing a vaccination model for studies of protective immunity in onchocerciasis. The influence of host genetics on worm recoveries and development (growth and moulting rate) was analysed in a panel of inbred mice (CBA, BALB/c, DBA/2, SJL, 129J, C57BL/10 (B10), C3H/He and NIH), together with mice of BALB and B10 backgrounds with different major histocompatibility complex (H-2) genes (BALB/c, BALB.K, BALB.B and B10, B10.D2/n, B10.BR, B10.S). Parasite recoveries and development were similar in all mouse genotypes tested. They were unaffected by procedures designed to block or modulate phagocytic cell function with carbon or carrageenan, or to suppress inflammation by treatment with hydrocortisone acetate. A comparison of chambers sealed with membranes designed to admit (5·0 μm pore size) or exclude (0·2 μm pore size) host cells demonstrated no effect on the percentage recovery of living larvae, although dead larvae were more frequently retrieved when cells were excluded. Recoveries and rates of development of larvae implanted into immunodeficient scid mice and athymic Hooded rats were similar to those recorded in immunocompetent controls. We conclude that host genetic factors and immunocompetence are not significant determinants of survival, growth or development of O. lienalis larvae implanted within micropore chambers into naive mice. Despite its limitations, the use of this system merits further investigation as an approach to the study of protective immunity against developing larvae in onchocerciasis.

The genetic influences upon host variation in eosinophilia and resistance to helminth infection, and the relationship between these parameters, was investigated in 9 inbred and 3 hybrid strains of mice infected with Mesocestoides corti. Blood, bone marrow, spleen and peritoneal fluid eosinophilia were far higher in SJL mice than in any other inbred strain. SWR, NIH, C3H and BALB/c mice were high responders to M. corti whereas CBA and 3 congenic strains sharing the B10 background (C57BL/10, B10.S, B10.G) were low responders. Some of the genes for high eosinophil responsiveness appeared to be dominant, as F1 hybrids from high and low response parental strains were intermediate to high in response to infection. SJL and NIH strains were highly susceptible to infection with M. corti, larval burdens at 21 days after infection with 100 tetrathyridia being considerably higher (>1000) than all other strains. BALB/c (≃ 700 larvae) were designated susceptible, SWR (>400 larvae) were resistant and the BIO congenics (<400 larvae) were highly resistant. Genes influencing resistance also appeared to be dominant, as F1 hybrids between resistant and susceptible parental strains were intermediate to resistant on infection. The overall response patterns indicate a direct correlation between susceptibility to infection and high eosinophil responsiveness, but this relationship is not consistent in all strains.

A new isolate of Trypanosoma musculi has been derived from organisms recovered from Mus spretus captured in Lisbon, Portugal. The time-course and profiles of infection with this isolate in inbred mice have been compared with those obtained with the existing Partinico II isolate. Infections with the Portuguese isolate are less intense, and controlled more quickly than those with the Partinico isolate. As with the latter, there are marked mouse strain-dependent influences on infection with the Portuguese isolate, but these strain-dependent characteristics differ considerably with each isolate. For example, NIH mice were the most susceptible to the Partinico II isolate, but virtually refractory to the Portuguese isolate. Mice exposed to infection with one isolate show complete immunity to both homologous and heterologous challenge infections. These striking interactions between host and parasite genotype are discussed in terms of immunological influences on infection.

Toxocara canis, the parasitic roundworm of dogs, can infect a number of paratenic hosts, such as mice and humans, due to the widespread dissemination of its ova in the environment. In these paratenic hosts, larvae have been shown to exhibit a predilection for the central nervous system, resulting in an increasing number of parasites migrating to the brain as infection progresses. In an initial experiment, we investigated the differential brain involvement of T. canis in 7 strains of inbred mice, and chose 2 strains, susceptible (BALB/c) and resistant (NIH) to cerebral infection. In a second experiment, both strains were investigated in terms of course of migration, larval accumulation, and behavioural response to T. canis infection. Results revealed that infected BALB/c mice took significantly longer to drink from a water source (following a period of deprivation), compared with control mice, indicating some degree of memory impairment. Cerebral larval recoveries from both strains of mice demonstrated variation between the two experiments, suggesting that larval burdens may not be a reliable indicator of susceptibility or resistance to T. canis infection. The percentage of total recovered larvae in each organ may be a better representation of larval distribution. Our model system may provide insights into the impact of chronic geohelminth infection on cognitive development.