This likely reflects the fact that TNF expression induced by LPS is known to peak earlier than 3 hours. Likewise, there were other inflammatory response genes differentially expressed after LPS stimulation that were detected in both PBMC and monocytes. These included genes that were upregulated, such as monocyte chemotactic protein 2 , and genes that were downregulated, such as dendritic cell immunoreceptor , confirming that genes strongly differentially expressed in OTX015 monocytes can be detected in PBMC. Of particular interest were genes that had significant differential expression after LPS stimulation in monocytes that were not detected when PBMC were used for analysis. The linker for activation of T cells gene, known to be upregulated in monocytes, was significantly upregulated at 3 hours in the Mono+ and Mono2 samples. Conversely, expression of this gene was significantly downregulated in the MonoD sample, resulting in an overall lack of change in expression in the PBMC sample. There were, however, also genes where the differential expression in response to LPS appeared markedly different between monocytes and PBMC, but were detectable in both samples. For example, the small inducible cytokine A5 was highly differentially expressed in the Mono+ sample. Although there was no differential expression in the MonoD sample, the marked expression in monocytes resulted in the gene remaining detectable in PBMC, despite the dilutional effects of the nonmonocytes. There were in addition genes in which downregulation of expression in monocytes was more significant than in PBMC. These included histone deacetylase 4 , and acyloxyacyl hydrolase, where in both cases the differential expression in the MonoD sample was negligible or even slightly upregulated. These examples highlight the different effects of non-monocyte cells on overall expression in PBMC, obscuring or diluting the expression detectable in monocytes. The known proportion of monocytes and non-monocytes within the PBMC was used to predict gene expression in PBMC. This was done by calculating the reduction in fold change in gene expression that would occur in PBMC with different expression levels in non-monocytes. Increased expression in non-monocytes leads to greater dilution of the fold change in PBMC. This is illustrated by expression of the IL-1a gene. At 24 hours, IL-1a is expressed only in monocytes and the fold change is therefore the same in monocytes and PBMC. In contrast, at 3 hours IL-1a is expressed in non-monocytes at about one sixth of the level in monocytes and this results in a reduction in fold change in PBMC. There were a few genes that were differentially expressed in opposite directions in monocytes and PBMC after stimulation with LPS. Examples included granzyme A and c-type lectin. In both cases, expression in the MonoD sample was in the opposite direction to the expression in the monocyte samples, which resulted in opposite overall expression in PBMC.