Using factual information of uncertain truth value as the stimulus material, previous investigators have found that repeated statements are rated more valid than non‐repeated statements. Experiments 1 and 1A were designed to determine if this effect would also occur for opinion statements and for statements initially rated either true or false. Subjects were exposed to a 108‐statement list one week and a second list of the same length a week later. This second list was comprised of some of the statements seen earlier plus some statements seen for the first time. Results suggested that all types of repeated statements are rated as more valid than their non‐repeated counterparts. Experiment 2 demonstrated that the validity‐enhancing effect of repetition does not occur in subject domains about which a person claims not be knowledgeable. From the results of both studies we concluded that familiarity is a basis for the judged validity of statements. The relation between this phenomenon and the judged validity of decisions and predictions was also discussed.

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Synopsis The field of regenerative medicine research is rapidly expanding for both human and animal model organisms. One area of particular interest to many equine researchers is the possibility of isolating or generating cells that are pluripotent, therefore capable of producing differentiated cell types derived from all three primary germ layers. Currently, several reports of equine embryonic stem-like (ES) cell isolation can be found in the literature. Meanwhile, other groups are working to produce equine induced pluripotent stem (iPS) cells. The focus of this chapter is to provide a background summary of the essential features needed to characterize a cell type as pluripotent in any species, specific challenges in using the horse as a model organism for pluripotent cell generation, and a brief introduction of current and upcoming clinical trials using ES/iPS cells.

A long-term goal of mesenchymal progenitor cell (MPC) research is to identify cell-surface markers to facilitate MPC isolation. One reported MPC feature in humans and other species is lack of CD14 (lipopolysaccharide receptor) expression. The aim of this study was to evaluate CD14 as an MPC sorting marker. Our hypothesis was that cells negatively selected by CD14 expression would enrich MPC colony formation compared with unsorted and CD14-positive fractions. After validation of reagents, bone marrow aspirate was obtained from 12 horses. Fresh and cultured cells were analyzed by flow cytometry and reverse transcription and quantitative polymerase chain reaction to assess dynamic changes in phenotype. In fresh samples, cells did not consistently express protein markers used for lineage classification. Short-term (2-day) culture allowed distinction between hematopoietic and nonhematopoietic populations. Magnetic activated cell sorting was performed on cells from 6 horses to separate adherent CD14 þ from CD14 À cells. MPC colony formation was assessed at 7 days. Cells positively selected for CD14 expression were significantly more likely to form MPC colonies than both unsorted and negatively selected cells (P 0.005). MPCs from all fractions maintained low levels of CD14 expression long term, and upregulated CD14 gene and protein expression when stimulated with lipopolysaccharide. The equine CD14 molecule was trypsin-labile, offering a plausible explanation for the discrepancy with MPC phenotypes reported in other species. By definition, MPCs are considered nonhematopoietic because they lack expression of molecules such as CD14. Our results challenge this assumption, as equine MPCs appear to represent a descendant of a CD14-positive cell.