Discriminating depth in corrugated stereo surfaces: facilitation by a pedestal is explained by removal of uncertainty

With luminance gratings, psychophysical thresholds for detecting a small increase in the contrast of a weak ‘pedestal’ grating are 2–3 times lower than for detection of a grating when the pedestal is absent. This is the ‘dipper effect’ – a reliable improvement whose interpretation remains controversial. Analogies between luminance and depth (disparity) processing have attracted interest in the existence of a ‘disparity dipper’. Are thresholds for disparity modulation (corrugated surfaces), facilitated by the presence of a weak disparity-modulated pedestal? We used a 14-bit greyscale to render small disparities accurately, and measured 2AFC discrimination thresholds for disparity modulation (0.3 or 0.6 c/deg) of a random texture at various pedestal levels. In the first experiment, a clear dipper was found. Thresholds were about 2× lower with weak pedestals than without. But here the phase of modulation (0 or 180 deg) was varied from trial to trial. In a noisy signal-detection framework, this creates uncertainty that is reduced by the pedestal, which thus improves performance. When the uncertainty was eliminated by keeping phase constant within sessions, the dipper effect was weak or absent. Monte Carlo simulations showed that the influence of uncertainty could account well for the results of both experiments. A corollary is that the visual depth response to small disparities is probably linear, with no threshold-like nonlinearity.

Apoptotic cell‐associated ICAM‐3 in the phagocytic removal of apoptotic cells

Apoptosis is a highly controlled cell death programme that culminates in the exposure of molecular ‘flags’ at the dying cell surface that permit recognition and removal by viable phagocytes. Failure to efficiently remove dying cells can lead to devastating inflammatory and autoimmune disorders. The molecular mechanisms underlying apoptotic cell surface changes are poorly understood. Our previous work has shown an apoptosis-associated functional change in ICAM-3 (a heavily glycosylated, leukocyte-restricted Immunoglobulin Super-Family member) resulting in a molecular ‘flag’ to mediate corpse removal. Here we detail apoptosis-associated changes in ICAM-3 and define their role in ICAM-3’s novel function in apoptotic cell clearance. We show ICAM-3 functions to tether apoptotic leukocytes to macrophages via an undefined receptor. Though CD14 has been suggested as a possible receptor for apoptotic cell-associated ICAM-3, we demonstrate ICAM-3 functions for apoptotic cell clearance in the absence of CD14. Furthermore, we demonstrate leukocytes display early changes in cell surface glycosylation and a marked reduction in ICAM-3, a change that correlates reduced cell volume throughout apoptosis. This loss of ICAM-3 occurs via shedding of ICAM-3 in microparticles (‘apoptotic bodies’). Such microparticles are potent chemoattractants for macrophages. Notably, microparticles from ICAM-3-deficient leukocytes are significantly less chemoattractive than microparticles from their ICAM-3-replete counterparts. These data support the hypothesis that ICAM-3 acts as an apoptotic cell-associated ligand to tether dying cells to phagocytes in a CD14-independent manner. Furthermore our data suggest that released ICAM-3 may promote the recruitment of phagocytes to sites of apoptosis.

Inhibitory effects of persistent apoptotic cells on monoclonal antibody production in vitro:simple removal of non-viable cells improves antibody productivity by hybridoma cells in culture

Cells undergoing apoptosis in vivo are rapidly detected and cleared by phagocytes. Swift recognition and removal of apoptotic cells is important for normal tissue homeostasis and failure in the underlying clearance mechanisms has pathological consequences associated with inflammatory and auto-immune diseases. Cell cultures in vitro usually lack the capacity for removal of non-viable cells because of the absence of phagocytes and, as such, fail to emulate the healthy in vivo micro-environment from which dead cells are absent. While a key objective in cell culture is to maintain viability at maximal levels, cell death is unavoidable and non-viable cells frequently contaminate cultures in significant numbers. Here we show that the presence of apoptotic cells in monoclonal antibody-producing hybridoma cultures has markedly detrimental effects on antibody productivity. Removal of apoptotic hybridoma cells by macrophages at the time of seeding resulted in 100% improved antibody productivity that was, surprisingly to us, most pronounced late on in the cultures. Furthermore, we were able to recapitulate this effect using novel super-paramagnetic Dead-Cert Nanoparticles to remove non-viable cells simply and effectively at culture seeding. These results (1) provide direct evidence that apoptotic cells have a profound influence on their non-phagocytic neighbors in culture and (2) demonstrate the effectiveness of a simple dead-cell removal strategy for improving antibody manufacture in vitro.

Dapsone hydroxylamine induces premature removal of human erythrocytes by membrane reorganization and antibody binding

N-hydroxylation of dapsone leads to the formation of the toxic hydroxylamines responsible for the clinical methaemoglobinaemia associated with dapsone therapy. Dapsone has been associated with decreased lifespan of erythrocytes, with consequences such as anaemia and morbidity in patients treated with dapsone for malaria. Here, we investigated how dapsone and/or its hydroxylamine derivative (DDS-NHOH) induced erythrocyte membrane alterations that could lead to premature cell removal.