C‐Reactive Protein Triggers Calcium Signalling in Human Neutrophilic Granulocytes via Fcγ RII a in an Allele‐Specific Way

• Published in: Scandinavian journal of immunology Vol. 77; no. 6; pp. 442 - 451
• Main Authors: Aas, V., Sand, K. L., Åsheim, H.‐C., Benestad, H. B., Iversen, J.‐G.
• Format: Journal Article
• Language: English
• Published: 01.06.2013
• ISSN: 0300-9475; 1365-3083
• DOI: 10.1111/sji.12049

Abstract C ‐reactive protein (CRP) binds to F cγ‐receptors, F cγRIIa ( CD 32) with high affinity and to F cγ R Ia ( CD 64) with low affinity. The binding to CD 32 has been shown to be allele specific, that is, it binds to R / R 131 but not to H / H 131. Little is known about the cooperation of CRP and neutrophilic granulocytes ( PMN s) in inflammatory reactions. The purpose of the present study was to examine CRP signalling in human PMN s, and whether this signalling is also allele specific. Cytosolic calcium of PMN was measured in a single‐cell digital imaging system. Receptor expression and polymorphism were studied by real‐time RT ‐ PCR , flow cytometry and standard PCR . C ‐reactive protein induced cytosolic calcium signals in PMN s from homozygote R / R 131donors, but not in PMN s from heterozygote R/H131 donors. However, after the heterozygote PMN s had been incubated with IFN ‐γ (100 U/ml) for 2 h, both the proportion of cells responding and the size of the CRP ‐induced calcium signals increased. IFN ‐γ increased mRNA expression of CD 64 about fivefold and surface protein expression of CD 64 about fourfold. The calcium signal elicited by CRP was augmented by PMN adhesion to fibronectin, but almost totally abrogated by sphingosine kinase inhibitors. The signals were partly dependent on calcium influx. In conclusion, calcium signalling instigated by CRP in human PMN is F cγ R IIa allele specific, as R / R 131 responded to CRP , whereas R / H 131 did not. However, increased expression of FcγRIa ( CD 64), stimulated by IFN ‐γ, can augment calcium signalling by CRP in low‐responders. This suggests that the state of the PMN s, as well as the genetic origin, affect sensitivity for CRP .