Contextual effects on perceived three-dimensional shape.

Binocular disparity is a powerful cue for the perception of depth. The accuracy with which observers can judge depth from disparity can, however, be very poor. This has been attributed to difficulties associated with the scaling of disparity to take account of distance (Johnston, 1991). We test potential strategies that could be used to improve this scaling. Using the depth-to-width ratio task introduced by Bradshaw, Parton, and Eagle (1998), observers adjusted a depth interval to match the vertical distance between two points. The first experiment examined the effect of placing additional visual stimuli between the observer and the target. Despite the potential of these stimuli to provide reliable distance information, the accuracy of depth settings did not change. The second experiment demonstrated that the degree of binocular correlation present in natural images provides useful distance information, and investigated whether this is used by observers in scaling disparity. To do this, we measured whether varying the magnitude of relative disparity presented in the surround of the target affected depth settings. No such effect was observed. We conclude that the effect of information presented in the surrounding context on settings of depth is limited to those situations in which it provides direct information about the distance to the target.

Amino acid differences in the N-terminus of C(H)2 influence the relative abilities of IgG2 and IgG3 to activate complement.

The four human IgG isotypes are highly conserved in amino acid sequence, but show differential ability to activate complement (C'): IgG3 and IgG1 are very active, IgG2 is active under certain conditions, and IgG4 is inactive. Although the second constant domain [C(H)2] is critical for C' activation, the individual amino acids that confer isotype-specific activity have not been identified. We have generated a series of mutants between IgG2 and IgG3, resulting in the exchange of the four N-terminal and six C-terminal polymorphic residues within C(H)2. Mutants containing the N-terminus of the C(H)2 of IgG3 were as effective as wildtype IgG3 in C1q binding, C1 activation and terminal complex (MAC) formation, but had reduced ability to effect C'-mediated lysis. IgG2 and mutants containing the N-terminal portion of the C(H)2 of IgG2 were reduced compared to IgG3 in activating C1, binding C1q and inducing assembly of the MAC, and were inactive in mediating lysis of target cells. Thus, the amino acid sequence differences in the N-terminus of C(H)2 play a critical role in determining the relative abilities of IgG2 and IgG3 to bind C1q and activate the C' cascade although additional residues of C(H)2 must be involved in mediating optimal target cells lysis. The sequence of the N-terminus of C(H)2 was less critical in determining C4 and C3 binding. Characterization of domain exchange mutants suggests that intermediate steps may be partly dependent on domains other than C(H)2. IgGs that do not direct target cell lysis nevertheless activate intermediate steps in the pathway, which may contribute to immune complex-associated disorders.

The quality of initial function following renal transplantation determined by creatinine elimination kinetics. Comparison of Minnesota antilymphocyte globulin and cyclosporine induction immunosuppression.

To compare the effect of type of induction immunosuppression on the quality of initial renal allograft function, we identified 35 cadaver donor kidney pairs in which one recipient of a kidney from a given pair received induction immunosuppression with Minnesota antilymphocyte globulin (MALG group) while the recipient of the contra-lateral kidney received cyclosporine from day zero (CsA group). In the absence of an existing quantitative measure to assess and compare the status of those grafts that function primarily, we defined the half-life of creatinine elimination (t1/2SCr) as such an outcome measure based on a review of creatinine elimination kinetics. All organs were procured with in-situ perfusion and en-bloc removal. Total cold storage times, rewarm times, and perioperative management were comparable for the two groups. In the MALG group, the mean t1/2SCr) was not different from that in the CsA group (1.38 +/- 0.96 days vs 1.35 +/- 1.2 days P = NS). Multiple regression analysis performed on the differences in recipient age, number of DR-B locus matches, total cold ischemia time, rewarm time, and central venous pressure at reperfusion of a given donor pair demonstrated no significant impact of any of these differences on the difference in t1/2SCr for the same pair set in this sample. The nadir of serum creatinine achieved in the first five days posttransplant was somewhat higher in the CsA group (234 +/- 131 mumol/L) as compared with the MALG group (200 +/- 132 mumol/L) but the difference was not significant. A similar nonsignificant trend was observed in the comparison of mean serum creatinine values at 30 days posttransplant (MALG group: 158 +/- 62 mumol/L vs. CsA group: 200 +/- 141 mumol/L). Only one of seventy recipients (CsA group) was dialyzed within the first 5 days posttransplant for an overall incidence of ATN of less than 2%. Fourteen of 35 (40%) recipients in both groups received treatment for acute rejection. The mean time to first treatment for acute rejection episode was shorter in the CsA group than the MALG group (10 +/- 8 days vs 23 +/- 24 days, P = 0.055). Graft survival at one year was not different for the two groups (92% vs. 87% for the MALG and CsA groups respectively, P = NS).(ABSTRACT TRUNCATED AT 400 WORDS)