, Gaithersburg, MD, USA) was added. Following a 30-min incubation, the
plates were washed and 100 µl/well of ABTS substrate [2,2′-azino-bis-(3-benzthiazoline-6-sulphonic acid)] (KPL) was added. Colour development was stopped after 30 min by the addition of 50 µl/well of 1% sodium dodecyl sulphate (SDS) (Sigma-Aldrich). The light absorption at 415 nm was measured with a Bioassay HTS 7000 plate reader (PerkinElmer, Waltham, MA, USA). Data analysis was perormed with spss version 11·5 (SPSS Inc., Chicago, IL, USA). CYC202 order Analysis of variance with Tukey’s post-hoc test was used to detect differences in continuous variables across groups controlling for assay date. Pearson’s correlation coefficient Dorsomorphin nmr was used to study the relationship between
numeric variables. The t-test or the non-parametric Mann–Whitney rank sum test were used to test for differences between the means of two groups. Differences were considered statistically significant if P < 0·05. All tests were two-tailed. Of 344 individuals recruited in the cross-sectional study we selected 72 individuals with either low (between 253–388 copies/red cell), medium (443–579 copies per red cell) or high (581–1125 copies per red cell) red cell CR1 expression (Fig. 1a). Because the red cell CR1 level determines the IC binding capacity, we measured this parameter in each individual. There was no significant difference in the IC binding capacity between low and medium CR1 expressors (Fig. 1b). However, the IC binding capacity correlated well with the CR1 level (Fig. 1c). We confirmed that IC-dependent TNF-α production by macrophages is inhibited by Fc fragments, and therefore
it is dependent on Fcγ receptors (Fig. 2a). We then set out to investigate whether binding of free opsonized ICs to erythrocytes leads to inhibition of the IC-mediated stimulation of macrophages and whether, conversely, IC-loaded erythrocytes can stimulate macrophages to release TNF-α. As can be seen in Fig. 2b, incubation of red cells with opsonized ICs inhibited the production of TNF-α by the macrophages (P < 0·001) and IC-loaded erythrocytes stimulated production of TNF-α compared to non-IC bearing erythrocytes (P < 0·001). To understand the influence of red cell G protein-coupled receptor kinase CR1 expression level on their inhibitory and stimulatory capacity we analysed the above data by CR1 expression level. Medium and high CR1-expressing red cells were more effective at inhibiting the IC-mediated stimulation of macrophages than low CR1-expressing erythrocytes (Fig. 3a). However, there was no significant difference between medium and high CR1-expressing erythrocytes. We observed no significant difference in the ability of IC-loaded erythrocytes with different CR1 expression level to stimulate TNF-α production from macrophages (Fig. 3b).