Near-field quantification of complement receptor 1 (CR1/CD35) protein clustering in human erythrocytes.

We investigate the distribution of the membrane protein complement receptor 1 (CR1/CD35) in human erythrocyte membrane ghosts using scanning near-field optical microscopy. Recent studies have demonstrated that levels of Aβ peptide, associated with Alzheimers disease (AD) and present in brain and peripheral blood, vary significantly when bound by complement C3b-dependent adherence to CR1. It is unknown why patients with AD have a markedly impaired ability to bind Aβ to CR1 via this mechanism, but one possibility is a defect in the localization and/or conformation of CR1 in the membrane. Scanning near-field optical microscopy does not require the harsh preparation of electron microscopy techniques and may therefore be better suited for measuring membrane protein distributions. The clustering phenomenon of CR1 identified in electron microscopy studies is confirmed and quantified. The standard deviation of the inter-cluster spacing of CR1 is constant (79 ± 9 nm) across erythrocytes with between 61 and 124 clusters per membrane ghost.