Repeated mobility testing for later artificial visual function evaluation

The study investigates the utility of a newly designed mobility test for repeated testing of visual function in patients with severe visual impairment and future application in evaluating functional progress in patients with artificial vision. Ten subjects divided into three groups based on visual acuity (VA) ranging from light perception to 20/200 and reduced visual field (VF) were included in the study. The mobility test consisted of using a set of four different but structurally similar and relatively short mazes having a constant number of obstacles of various sizes. The subjects, divided into three groups by acuity, passed through each course several times. In general, the patients with better VA had a larger extent of VF. Average speed and number of contacts were recorded as measures of performance. The average passing times of the groups through the courses were significantly different (p = 0.03), which was influenced by VA and VF. There was no significant difference in average number of contacts between the groups (p = 0.15). The mobility test proved to be appropriate for gaining statistically relevant results in repeated individual testing of patients with severe vision impairment. Results show promise for use this mobility test as a tool for assessing visual function of patients undergoing implantation of a visual prosthesis for artificial vision.

[Development of an epiretinal prosthesis for stimulation of the human retina]

Degenerations of the outer retina in retinal diseases such as retinitis pigmentosa lead to blindness due to photoreceptor loss. A therapeutic option for visual rehabilitation is presently not available. Over the last few years, a retinal prosthesis has been developed and its use has been tested in animal experiments as well as in humans. With the epiretinal implant images of the environment are taken by a camera, these data are transmitted to an intraocular encoder, and the retina is electrically stimulated by a retinal stimulator placed epiretinally. The stimulation electrodes are placed as flexible microcontact electrodes by pars plana vitrectomy in an epimacular position. The threshold is determined by stimulations of increasing amplitudes. Initial results of acute epiretinal stimulation using an epiretinal implant in legally blind patients demonstrate that acute epiretinal stimulation of the human retina is feasible and safe.

Band 3 protein clustering on human erythrocytes promotes binding of naturally occurring anti-band 3 and anti-spectrin antibodies

Recognition of senescent and oxidatively stressed human erythrocytes appeared to be initiated by band 3 clustering, followed by bivalent binding of naturally occurring anti-band 3 autoantibodies (anti-band 3 NAbs), and complement deposition. The number of RBC-associated anti-band 3 NAbs was, however, low compared to the total amount of IgG that bound in vitro to RBC containing band 3 oligomers. This implied the involvement of yet other types of NAb, among which we focussed on anti-spectrin NAbs, since eluates from RBC of thalassemic patients contained these NAbs. Binding of affinity-purified anti-band 3 and anti-spectrin NAbs was studied to RBC on which band 3 oligomers were generated by exoplasmic cross-linking. This pretreatment increased binding not only of (125)I-iodinated anti-band 3, but also of anti-spectrin NAbs by 7-10-fold at 0 degrees C in the presence of nearly physiological IgG and HSA concentrations. Binding of anti-spectrin NAbs was not to spectrin as judged from surface-labeling of RBCs that were pretreated with cross-linker. Binding was dose and time dependent in both cases. Moreover, binding of anti-spectrin NAbs was not competed by high concentrations of anti-band 3 NAbs and anti-spectrin NAbs even stimulated binding of anti-band 3 F(ab')(2) by 30%. This suggests that anti-spectrin NAbs bound to band 3 or a protein associated with band 3 by virtue of their inherent polyreactivity.

Tissue homeostatic role of naturally occurring anti-band 3 antibodies

Self antigens exposed to the immune system constitutively or in the process of tissue homeostasis may stimulate a TH2 type immunity giving rise to low titer, low affinity naturally occurring antibodies which are involved in actively maintaining peripheral tolerance to self and in tissue homeostatic clearance processes. In reviewing the tissue homeostatic aspect of naturally occurring antibodies to band 3 protein of the human erythrocyte membrane, we address crucial issues of how these and other types of naturally occurring antibodies (NAb) (eg. anti-spectrin NAb) gain functionality and how this can induce opsonization by complement C3b under physiological conditions. Exoplasmic, chemical cross-linking of band 3 protein is sufficient to increase specific anti-band 3 binding under physiological conditions. Formation of oligomers following this non-oxidative cross-linking protocol disfavors a recognition mechanism involving exposure of a neoantigen. New data on NAb binding to erythrocytes further demonstrates that specific binding of any low affinity NAb can only be determined in the presence of whole human IgG and physiological ionic strength, where competition of the predominantly positively charged NAb for binding to the negatively charged cell surface is high. Hence, specific and physiologically relevant binding of low affinity NAb is gained by bivalent binding and suppression of exclusive charge-charge interactions by other NAb sharing the range of pl values. Therefore, many investigations on NAb/cell interactions which have been carried out in the absence of whole IgG have yielded controversial data.