Resistance against natural killer cell cytotoxicity: analysis of mechanisms.

Target cell resistance against natural killer (NK) cell-mediated cytotoxicity obstructs NK cell-based immunotherapy of leukaemia. Several mechanisms of resistance have been described. Because of lack of simple assays for analysing these mechanisms, their relative impact on a given effector-target pair is mostly unknown. We here analysed the combination of the Granzyme B (GrB) enzyme-linked immunospot assay (ELISPOT) for the assessment of NK cell reactivity and cytotoxicity assays to estimate target cell escape mechanisms. Target cell recognition failure leads to negative GrB ELISPOT results, whereas target cell resistance shows positive GrB ELISPOT results in the absence of cytotoxicity. We confronted NK cells with the sensitive target cell line K562, and with the resistant cell lines ML2, SupB15 and Raji. ML2 cells sufficiently activated GrB-release whilst being resistant against cytotoxic granules of NK cells. Partial resistance of Raji results from the interaction of HLA class I with inhibitory killer immunglobulin-like receptors (KIR) on the NK cells. Failure of target recognition by HLA class I-KIR interaction, lacking ligands to stimulatory NK cell receptors and partial resistance to cytotoxic granules all contributed to resistance of SupB15. In conclusion, revealing the mechanisms of resistance against NK cell-mediated cytotoxicity may allow improving the results of NK-based immunotherapy.

Mooren's ulcer treated with a periosteal graft.

We report a case of recurrent Mooren's ulcer treated with an autogenous periosteal graft. The eye responded well to this therapy. Final visual acuity was 20/40 with spectacle correction of +2.00 + 2.50 X 165.

Quantitative descriptors of corneal shape derived from computer-assisted analysis of photokeratographs.

The goal of this retrospective study was to derive clinically useful quantitative measures of corneal shape from computer-assisted analyses of photokeratoscope photographs. Algorithms were developed to determine a new index of corneal symmetry, the Surface Asymmetry Index (SAI). The SAI correlated well with best spectacle-corrected visual acuity and may be useful clinically for predicting the level of spectacle-corrected visual acuity that could be expected based on the corneal surface topography in the otherwise normal eye of an individual patient. Algorithms were also developed to determine the centrally-weighted average corneal power and the power and location of the steepest and flattest corneal meridians. The average surface power and the power of the steepest meridian determined from the photokeratographs correlated well with values obtained using the keratometer in the retrospective series (correlation coefficient = 0.98 for the average surface power and 0.97 for the power of the steepest meridian).

Corneal compression sutures for the reduction of astigmatism after penetrating keratoplasty.

We placed interrupted 9-0 nylon sutures across the graft-host interface of ten eyes with more than 5 diopters of keratometric cylinder after penetrating keratoplasty in order to steepen the flattest corneal meridian and reduce the amount of corneal cylinder. Placement of compression sutures reduced corneal cylinder by an average of almost 6 diopters one week later. Average corneal cylinder was 5.1 diopters nine to 12 months after surgery. Best-corrected visual acuity with spectacles improved by an average of two Snellen lines (20/60 to 20/40) and uncorrected visual acuity improved by an average of one line (20/300 to 20/200). There were no complications related to placement of the sutures. This procedure provides a rapid and simple method for reducing astigmatism after penetrating keratoplasty.

The topography of normal corneas.

Previously we have analyzed photokeratographs to determine the topography of congenital, acquired, and surgically induced deformations of corneal shape. In this article, we survey the variety of corneal shapes found in both eyes of 22 individuals with normal corneas. The degree of correlation of the distribution of corneal power around the visual axis was striking for both eyes of 18 of the 22 individuals, as was the variability of the corneal topography of different individuals. The average centrally weighted corneal power determined from the photokeratographs correlated well with the average keratometric corneal power (r = .96). By defining the topographic features characteristic of normal corneas, we will be better able to diagnose corneal shape anomalies and understand the role such anomalies play in the degradation of vision.

Imaging of the cornea.

The aim of the LSU Eye Center Corneal Topography Project was to apply computer analysis to keratoscopy and develop graphic presentation methods to provide accurate and easily assimilated information regarding the status of patient corneal topography. The analysis contains four diagrams: a plot of the raw keratoscope data for quality control, a three-dimensional wire model of corneal surface power distribution, a plot of dioptric point surface powers, and a color-coded contour map of corneal surface powers. While the analysis uses a current generation 11 ring keratoscope for producing keratoscope photographs, it can be adapted to newer keratoscopes, which promise to give broader coverage of the corneal surface. Examples of normals and several surgical patients will be shown, including cases in which the method has pointed to potential refinements in the theory and application of refractive surgical techniques.