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The explosion of genuine high throughput technologies has allowed large compound libraries to be screened with ever increasing biological specificity, exacerbating the problem of lead candidate selection for subsequent drug development. To avoid creating a bottleneck, compounds identified from the high throughput screens undergo lead optimisation, a medium-throughput screen which allows ranking in terms of their basic absorption, distribution, metabolism, excretion (ADME) and toxicological properties. The historical role of the preclinical scientist in the drug discovery/development continuum has been to perform ADME and toxicology studies, simply to support the regulatory submission of lead candidates. This situation is, however, changing with the development of preclinical lead optimisation technologies (Approaches to High Throughput Toxicity Screening, London, Atterwill et al., 1999) facilitating the selection of leading candidates, thereby bridging the gap between high throughput efficacy screens and traditional safety assessment programmes.

The interaction of human serum with oligodendroglia was investigated in vitro using purified cultured neonatal rat oligodendrocytes. Previous evidence for antibody independent classical pathway complement activation was confirmed; the results also showed a deficit in the protection of rat oligodendrocytes from complement attack suggesting a deficiency in the expression of terminal regulatory proteins of the complement cascade. Thus, rat oligodendrocytes are selectively sensitive to normal serum due both to complement activation and impaired protection from terminal complement attack.

A high non-specific background fluorescence signal was observed when cell surface antigen analysis was carried out using flow cytometry on a cell sample which contained a high proportion of dead and dying cells. To overcome this problem it was necessary to analyse the cells in three stages. First the intact cells were identified by their forward (FWD) and 90 degree scatter profile. These cells were gated-on, then analysed on the basis of their FWD scatter and propidium iodide (PI) signal, allowing the dead PI positive cells to be gated out. The PI negative cells were then displayed using their 90 degree scatter and fluorescence signals following staining with the irrelevant antibody control. This revealed a population of dead cells, which despite being PI negative, were non-specifically binding antibody molecules. Such multiparameter analysis permitted the successful analysis of cell surface antigens in preparations of low viability by gating out the high background fluorescence associated with dead PI positive and negative cells.