No abstract

Background The complement system is a central component of the innate immune system. Constitutive biosynthesis of complement proteins is essential for homeostasis. Dysregulation as a consequence of genetic or environmental cues can lead to inflammatory syndromes or increased susceptibility to infection. However, very little is known about steady state levels in children or its kinetics during infection. Methods With a newly developed multiplex mass spectrometry-based method we analyzed the levels of 32 complement proteins in healthy individuals and in a group of pediatric patients infected with bacterial or viral pathogens. Findings In plasma from young infants we found reduced levels of C4BP, ficolin-3, factor B, classical pathway components C1QA, C1QB, C1QC, C1R, and terminal pathway components C5, C8, C9, as compared to healthy adults; whereas the majority of complement regulating (inhibitory) proteins reach adult levels at very young age. Both viral and bacterial infections in children generally lead to a slight overall increase in complement levels, with some exceptions. The kinetics of complement levels during invasive bacterial infections only showed minor changes, except for a significant increase and decrease of CRP and clusterin, respectively. Interpretation The combination of lower levels of activating and higher levels of regulating complement proteins, would potentially raise the threshold of activation, which might lead to suppressed complement activation in the first phase of life. There is hardly any measurable complement consumption during bacterial or viral infection. Altogether, expression of the complement proteins appears surprisingly stable, which suggests that the system is continuously replenished. Fund European Union's Horizon 2020, project PERFORM, grant agreement No. 668303.

Background Monitoring 6-thiopurine S-methyltransferase (TPMT; EC 2.1.1.67) activity is especially important when patients are treated with 6-thiopurine drugs, since severe bone marrow toxicity may be induced if patients have deficient TPMT activity.

The proposed metabolic advantage of 6-thioguanine (6-TG) is the direct conversion into the pharmacologically active 6-thioguaninenucleotides (6-TGN). The authors assessed metabolic characteristics of 6-TG treatment in patients with Crohn's disease (N = 7) on therapy with 20 mg 6-TG. 6-thioguanine-monophosphate (6-TGMP), 6-thioguanine-diphosphate (6-TGDP), and 6-thioguanine-triphosphate (6-TGTP) were measured by high-performance liquid chromatography analysis in erythrocytes. Thiopurine S-methyltransferase activity and total 6-TGN levels were determined by standard methods. High interindividual variance in metabolite measurements was observed. Main metabolites were 6-TGTP (median = 531 pmol/8 x 10(8) red blood cells) and 6-TGDP (median = 199 pmol/8 x 10(8) red blood cells). Traces of 6-TGMP (median = 39 pmol/8 x 10(8) red blood cells) and 6-TG (2 patients) could be detected. 6-TGN levels correlated with 6-TGTP levels (r = 0.929, P = .003) and with the sum of separate nucleotides (r = 0.929, P = .003). No correlations were established between TPMT activity (median = 13 pmol/h/10(7)) and 6-TG metabolites. The 1-step metabolism of 6-TG still leads to high interindividual variance in metabolite concentrations. Total 6-TGN level monitoring may suffice for clinical practice.

No abstract