A comparison of ex vivo cytokine production in venous and capillary blood
We performed a randomized study of the immunological effects of an early measles vaccine given at 4·5 months of age and aimed to obtain venous samples from the infants at baseline and 6 weeks later. If this was not feasible, a capillary sample was obtained. We analysed baseline samples from the first 50 children enrolled in the study to investigate the potential differences in ex vivo cytokine production between venous blood and capillary blood. We also obtained paired venous and capillary blood samples from 11 adult volunteers. Whole blood was stimulated with lipopolysaccharide (LPS) [a Toll‐like receptor (TLR)‐4 ligand], (S)‐(2, 3‐bis (palmitoyloxy)‐(2‐RS)‐propyl)‐N‐palmitoyl‐(R)‐Cys‐(S)‐Ser‐(S)‐Lys4‐OH, trihydrochloride (PAM3Cys) (a TLR‐2 ligand), phytohaemagglutinin (PHA) or purified protein derivative (PPD). Cytokine concentrations in the supernatants were assessed by a multiplexed assay and were compared between venous and capillary samples in both infants and adults. The production of both the pro‐ and the anti‐inflammatory cytokines, tumour necrosis factor (TNF)‐α and interleukin (IL)‐10, was higher in cultures of capillary blood compared with venous blood. This was found in non‐stimulated control samples as well as in blood stimulated with PAM3Cys and PPD. Adults produced more IL‐5 in venous blood than in capillary blood upon PHA stimulation. We found no other difference in the levels of IL‐5 or IFN‐γ between venous and capillary blood. In capillary blood we found sex differences in response to PHA but this was not the case in venous blood. We found significant differences in the production of cytokines between venous and capillary blood. Such differences should be taken into account when setting up immuno‐epidemiological studies.