Screening for amblyopia: a comparison of paediatric letter tests

AIMS/BACKGROUND

The measurement of visual acuity is the most widely accepted indicator of amblyopia and is thought by some to be the only effective screening test. The aim of this study was to investigate the effectiveness of the traditional single optotype Sheridan-Gardiner test (SGT) in the measurement of visual acuity and the detection of amblyopia, compared with the log based linear format Glasgow acuity cards (GAC).

METHODS

In the present study visual acuity was measured monocularly in 702 primary 1 schoolchildren using both acuity tests.

RESULTS

A significant difference was found in the mean (SD) visual acuity measured with GAC (0.9 (0.08) modified logMAR) and SGT (1.13 (0.09) modified logMAR), df = 632, t = -59.08, p = 0.0001. The majority of children (89.3%) achieved visual acuities better than 6/6 in either eye when using the single optotype test. If the 95% confidence limits for a significant interocular difference in acuity are used as-criteria for the detection of unilateral amblyopia, GAC were found to be the most sensitive, correctly identifying 100%, while SGT identified 55% of the children with unilateral amblyopia.

CONCLUSION

The results of this study highlight several problems with both the test format and testing procedure in the present school screening system.

Clinical evaluation of infrared autorefractors for use in contact lens over refraction

We examined the ability of autorefractors to provide an accurate means of contact lens over-refraction measurement. Over-refraction measures, performed using six commercially available automated infrared autorefractors and retinoscopy, were compared with subjective refraction. A total of 40 contact lens wearers (20 soft lens wearers and 20 rigid gas permeable (RGP) lens wearers) participated in the study. All six autorefractors were able to provide over-refraction measures in all subjects. Data analysis revealed differences in autorefractor performance between the two types of contact lens wearer with greater accuracy and lower variability being found in the soft lens wearing subjects compared with the RGP group. The level of agreement between retinoscopy and subjective over-refraction results was lower in soft lens wear and higher in RGP wear than the levels found between the autorefractor and subjective over-refraction measures. We conclude that autorefractors provide a useful means of measuring contact lens over-refraction in soft lens wearers. Over-refraction results should be treated more cautiously in RGP wearers.

A voltage-operable current is involved in Ca2+ entry in human lymphocytes whereas ICRAC has no apparent role

Presently, it is thought that a non-voltage-gated current is responsible for activation-induced Ca2+ entry in nonelectrically excitable cells such as lymphocytes. However, it has also been proposed that the pathway instead involves a second messenger-regulated Ca2+ channel that is voltage operable, where "voltage operable" is defined as an intrinsic property of the channel protein(s) rather than a requirement of normal gating. To evaluate the contribution of these currents to activation-induced Ca2+ influx, each was examined with respect to its ability to account for Ca2+ influx as reported by Ca(2+)-sensitive dyes. We identified a set of reagents, nordihydroguaiaretic acid and various calmodulin inhibitors, that inhibits Ca2+ entry and blocks the voltage-operable current but leaves the non-voltage-gated current unaltered. Further-more, nordihydroguaiaretic acid inhibited Ca(2+)-dependent proliferation of mitogen-activated human peripheral blood mononuclear cells or Jurkat T cells and specifically blocked Ca(2+)-dependent interleukin 2 production by Jurkat T cells to a degree similar to the immunosuppressant drug cyclosporin A. We also identified compounds, amiloride and Mn2+, that block the non-voltage-gated current but have no effect on either the voltage-operable current or Ca2+ entry. Correspondingly, amiloride had no effect on Ca(2+)-dependent proliferation of Jurkat cells. These observations imply that blockade of the non-voltage-gated current does not block either Ca2+ entry or Ca(2+)-dependent lymphocyte proliferation, whereas blockade of the voltage-operable current does. The data suggest that the voltage-operable current may be a mediator of activation-induced Ca2+ entry in lymphocytes.

Comparison of age-related changes in short-wavelength-sensitive cone thresholds between normals and patients with primary open-angle glaucoma

PURPOSE

To establish the effect of aging upon short-wavelength-sensitive cone (S-cone) sensitivity for both normals and patients with primary open-angle glaucoma (POAG).

METHODS

S-cone thresholds were established for the detection of blue test spots on a bright yellow adapting background. Detection thresholds for combined medium- and long-wavelength-sensitive cones (M/L-cones) were also established for a yellow test spot upon a yellow background. A group of 177 normal subjects (age range 20 to 80 years) and 46 glaucoma subjects were examined.

RESULTS

The rate of decline of S-cone sensitivity with increasing age was found to be similar in patients with POAG and age-matched normals (approximately 0.2 log units/decade), although S-cone sensitivity in the POAG population was significantly lower (p < 0.05) than that in age-matched normals by approximately 0.3 log units.

CONCLUSIONS

The results of the present investigation show an age-related decline in S-cone sensitivity for both normals and patients with POAG. The decline in S-cone sensitivity within the POAG population is similar to that occurring in normal subjects when the two populations are matched for age.

Lack of evidence for human T cell lymphotrophic virus type I or II infection in patients with systemic lupus erythematosus or rheumatoid arthritis

OBJECTIVE

Human retroviruses including human immunodeficiency virus (HIV) and human T cell lymphotrophic virus Types I and II (HTLV-I/II) have been associated with forms of connective tissue autoimmune diseases including systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). We looked for evidence of HTLV-I/II infection in a large population of SLE, RA, and control patients.

METHODS

One hundred fifteen patients with connective tissue autoimmune disease and other rheumatological disorders were screened for antibodies to HTLV-I/II by Western immunoblots (WIB). Due to the transforming characteristic of these retroviruses, the patients' peripheral blood mononuclear cells (PBMNC) were cultured in attempts to establish continuous cell lines. Furthermore, PBMNC culture supernatants were analyzed for reverse transcriptase activity and/or HTLV-I/II gag antigen production. The presence of HTLV-I/II proviral sequences in short term culture and fresh PBMNC was determined by Southern blot analysis and polymerase chain reaction (PCR), respectively. respectively.

RESULTS

All 115 patients were HTLV-I/II and HIV seronegative. Seventy-four attempts to establish PBMNC cell lines from 65 patients were unsuccessful with a mean culture survival time of 3.6 (+/- 1.4) months. Reverse transcriptase activity and HTLV-I/II gag antigen production were not detected in 51 and 16 culture supernatants tested, respectively. Cells from 11 patients tested by Southern blot analysis and from 57 patients tested by PCR were negative for HTLV-I/II related sequences.

CONCLUSION

Our results failed to establish an association between human retroviruses (HTLV-I/II and HIV) and SLE, RA, or other rheumatological disorders. However, these results do not rule out other exogenous or endogenous retroviruses that may play a role in the initiation and/or promotion of these diseases.

Pertussis toxin activates platelets through an interaction with platelet glycoprotein Ib

Platelets present a unique model to study the B-oligomer effects of pertussis toxin because they become activated in response to the B oligomer but are not susceptible to ADP-ribosylation by the holotoxin. In these studies, the B oligomer of pertussis toxin caused concentration-dependent platelet activation, as determined by increases in intracellular calcium concentration, dense granule secretion, and platelet aggregation. Stirring was required for pertussis toxin to increase intracellular calcium. A monoclonal antibody against platelet glycoprotein Ib abolished increases in intracellular calcium concentration and increased the latency and reduced the slope of the aggregation response elicited by the B oligomer. Pertussis toxin also evoked [14C]serotonin release from platelets, and this effect was inhibited, though not eliminated, by an antibody against platelet glycoprotein Ib. Binding of pertussis toxin to glycoprotein Ib was observed after nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These data suggest that the B oligomer of pertussis toxin induces platelet activation mediated, at least in part, by an interaction with platelet glycoprotein Ib.

Accommodative microfluctuations and pupil diameter

The nominally steady-state accommodation response exhibits temporal variations which can be characterized by two dominant regions of activity; a low frequency component (LFC < 0.6 Hz) and a high frequency component (1.0 < or = HFC < or = 2.1 Hz). There is no consensus as to the relative contribution made by each of the frequency components of the microfluctuations to the control of steady-state accommodation. We investigate the effect of variations in artificial pupil diameter (0.5, 1, 2, 3, 4 and 5 mm pupils) on the microfluctuations of accommodation, while three young emmetropic subjects view, monocularly, a photopic high contrast Maltese cross target placed at a dioptric distance equal to their open-loop accommodation level. Average power spectra were calculated for five accommodation signals, each of 10 sec duration, collected for each viewing condition at a sampling rate of 102.4 Hz using a continuously recording infrared objective optometer. For artificial pupil diameters < or = 2 mm the power of the LFC was found to increase as a function of reducing pupil diameter, while for artificial pupil diameters > 2 mm the LFC was found to be relatively constant. No systematic change in the HFC with varying artificial pupil diameter was observed. Changes in the root-mean-square (r.m.s.) value of the fluctuations with varying pupil diameter were significant (one-way ANOVA, F = 8.507, P = 0.0001, d.f. = 89) and showed a similar form to the changes in the LFC.(ABSTRACT TRUNCATED AT 250 WORDS)

Objective concurrent measures of open-loop accommodation and vergence under photopic conditions

PURPOSE

To investigate the relationship between photopic open-loop accommodation and vergence and the effect of mental effort on these positions.

METHODS

Twenty subjects (11 men and 9 women) viewed monocularly a photopic (25 cdm-2), high-contrast (90%) Maltese cross-target for 3 minutes, through a 0.5-mm pinhole drilled into an infrared filter. Accommodation was measured objectively at 1-second intervals using a Canon Autoref R-1 infrared optometer, and vergence was recorded continuously and objectively using a differential infrared eye tracking system.

RESULTS

Under passive viewing conditions there was a significant correlation between photopic open-loop accommodation and vergence (R = 0.671, P = 0.0012); for the majority of subjects the imposition of mental effort shifted the passive levels of both open-loop accommodation and vergence, but these shifts were unsystematic and uncorrelated (R = 0.259, P = 0.270). The active open-loop positions of accommodation and vergence were also found to be correlated (R = 0.692, P = 0.0007).

CONCLUSIONS

The influence of proximal stimuli can explain the correlations identified between photopic open-loop positions of accommodation and vergence. The uncorrelated responses of the accommodation and vergence systems to mental effort are likely to reflect interactions between various spatiotopic stimuli including mental effort and perceived proximity.

Effect of target luminance on microfluctuations of accommodation

It is feasible that small temporal variations in steady-state accommodation may provide feedback to the accommodation control system through changes in retinal image contrast and that this feedback may be used to maintain an optimal accommodation response. The complex waveform of microfluctuations is dominated by two distinct regions of activity; a low frequency component (LFC < 0.6 Hz) and a high frequency component (1.0 < or = HFC < or = 2.3 Hz). Whereas the HFCs appear to be correlated with some intraocular manifestation of arterial pulse the contribution of the LFCs to the control of steady-state accommodation is unclear. The present study investigates the effect of target luminance on the waveform of accommodative microfluctuations. Three young emmetropic observers viewed monocularly a high contrast (90%) Maltese cross target placed at a vergence equal to their dark-focus level of accommodation in a Badal stimulus system. The luminance of the target was varied from 0.002 to 11.63 cd m-2 in nine equal logarithmic steps. Five continuous accommodation signals were collected for each viewing condition at a sampling rate of 102.4 Hz, and average power spectra subsequently calculated with a frequency resolution of 0.1 Hz. One-way ANOVA revealed a significant variation in the root-mean-square (r.m.s.) value of the microfluctuations (F = 19.795, d.f. 124, P = 0.0001) which could be attributed mainly to increases in the r.m.s. value for the two lowest luminances (0.002 and 0.004 cd m-2). Power spectrum analysis revealed that these changes in the microfluctuations could be attributed to increases of power in the LFC.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical and blood bank factors in the management of platelet refractoriness and alloimmunization

Numerous independent and interdependent factors are involved in the posttransfusion platelet response. Factors such as ABO match and platelet age are related to circumstances potentially under the control of the blood bank physician and therefore may permit circumvention by an active transfusion service. On the other hand, factors such as fever or sepsis may be unavoidable, being related more to the individual patient or clinical condition. To evaluate which factors could be circumvented, we prospectively followed the 1-hour corrected count increments (CCIs) for 962 single-donor apheresis platelet transfusions to 71 refractory hematologic oncology inpatients, with concomitant recording of implicated factors. Stepwise regression analysis allowed for determination of which concurrent and confounding clinical-, patient-, and blood bank-related factors significantly affected the CCIs. Although many implicated factors proved to be independently associated with an increased or decreased CCI, we found that no single variable consistently explained the CCI variation across the patient population. Each patient appeared sensitive to one or a few particular factors, but because of marked intraindividual variation, it was not possible to identify a priori which factors were important for a given patient. The single exception was a solid-phase red blood cell adherence assay used to cross-match platelets, but only for alloimmunized patients. We also evaluated the utility of requesting HLA-matched platelets from the local suppliers and maintained a clear distinction between platelets simply ordered as HLA matched and actually HLA-identical platelets. Accounting for the confounding clinical-, patient-, and blood bank-related factors, the cross-match assay was a better predictor of an adequate CCI than ordering platelets as HLA matched.

Increased intracellular Ca2+ induces Ca2+ influx in human T lymphocytes

One current hypothesis for the initiation of Ca2+ entry into nonelectrically excitable cells proposes that Ca2+ entry is linked to the state of filling of intracellular Ca2+ stores. In the human T lymphocyte cell line Jurkat, stimulation of the antigen receptor leads to release of Ca2+ from internal stores and influx of extracellular Ca2+. Similarly, treatment of Jurkat cells with the tumor promoter thapsigargin induced release of Ca2+ from internal stores and also resulted in influx of extracellular Ca2+. Initiation of Ca2+ entry by thapsigargin was blocked by chelation of Ca2+ released from the internal storage pool. The Ca2+ entry pathway also could be initiated by an increase in the intracellular concentration of Ca2+ after photolysis of the Ca(2+)-cage, nitr-5. Thus, three separate treatments that caused an increase in the intracellular concentration of Ca2+ initiated Ca2+ influx in Jurkat cells. In all cases, Ca(2+)-initiated Ca2+ influx was blocked by treatment with any of three phenothiazines or W-7, suggesting that it is mediated by calmodulin. These data suggest that release of Ca2+ from internal stores is not linked capacitatively to Ca2+ entry but that initiation is linked instead by Ca2+ itself, perhaps via calmodulin.

A voltage-gated calcium channel is linked to the antigen receptor in Jurkat T lymphocytes

Activation of T lymphocytes results in an increase in intracellular Ca2+ due in large part to influx of extracellular Ca2+. Using the patch clamp technique, an inward current in Jurkat T lymphocytes was observed upon depolarization from a holding potential of -90 mV but not from -60 mV. This whole-cell current was insensitive to tetrodotoxin, carried by Ba2+, and blocked by Ni2+. Occupancy of the T lymphocyte antigen receptor increased the current's magnitude. These data suggest that antigen receptor-induced Ca2+ entry in T lymphocytes may be mediated by a voltage-regulated Ca channel.

Lymphocyte adhesion mediated by lymphocyte function-associated antigen-1. I. Long term augmentation by transient increases in intracellular cAMP

Lymphocyte adhesion to target cells is mediated, in part, by the interaction of lymphocyte function-associated Ag-1 (LFA-1) with intercellular adhesion molecule-1 (ICAM-1). Cells of the B cell line, JY, express both coreceptors and have been used as a model for intercellular adhesion mediated by these molecules. Elevation of the intracellular cAMP concentration ([cAMP]i), by any of several reagents, for periods as brief as 30 min, led to enhanced intercellular adhesion in a concentration dependent manner 5 to 8 h later. Two protein kinase A inhibitors, KT5720 and H-89, but not the protein kinase C inhibitor calphostin C, blocked the effects of elevated [cAMP]i. These data suggest a role for protein kinase A in this response. The adhesion augmented by increased [cAMP]i was due to LFA-1/ICAM-1 interactions between cells because it was blocked by either anti-LFA-1 or anti-ICAM-1 mAb. Elevated [cAMP]i induced cell surface patching of LFA-1, but not ICAM-1, and this redistribution preceded intercellular adhesion. Finally, redistribution of LFA-1 was not mediated by the cytoskeleton. These results suggest a model in which transient activation of protein kinase A results in increased local concentration of LFA-1 at the cell surface and in augmented long term adhesion mediated by this integrin.

Lymphocyte adhesion mediated by lymphocyte function-associated antigen-1. I. Long term augmentation by transient increases in intracellular cAMP

Lymphocyte adhesion to target cells is mediated, in part, by the interaction of lymphocyte function-associated Ag-1 (LFA-1) with intercellular adhesion molecule-1 (ICAM-1). Cells of the B cell line, JY, express both coreceptors and have been used as a model for intercellular adhesion mediated by these molecules. Elevation of the intracellular cAMP concentration ([cAMP]i), by any of several reagents, for periods as brief as 30 min, led to enhanced intercellular adhesion in a concentration dependent manner 5 to 8 h later. Two protein kinase A inhibitors, KT5720 and H-89, but not the protein kinase C inhibitor calphostin C, blocked the effects of elevated [cAMP]i. These data suggest a role for protein kinase A in this response. The adhesion augmented by increased [cAMP]i was due to LFA-1/ICAM-1 interactions between cells because it was blocked by either anti-LFA-1 or anti-ICAM-1 mAb. Elevated [cAMP]i induced cell surface patching of LFA-1, but not ICAM-1, and this redistribution preceded intercellular adhesion. Finally, redistribution of LFA-1 was not mediated by the cytoskeleton. These results suggest a model in which transient activation of protein kinase A results in increased local concentration of LFA-1 at the cell surface and in augmented long term adhesion mediated by this integrin.

Lymphocyte adhesion mediated by lymphocyte function-associated antigen-1. II. Interaction between phorbol ester- and cAMP-sensitive pathways

Ag independent adhesion between lymphocytes and target cells is mediated in part by the interaction between lymphocyte function associated Ag-1 (LFA-1) and its coreceptor intercellular adhesion molecule-1 (ICAM-1). Within minutes, PMA treatment of JY cells, which express both LFA-1 and ICAM-1, induced capping of LFA-1 and augmentation of intercellular adhesion lasting for several hours. However, over the course of 15 to 30 min, both of these events were blocked by elevation of intracellular cAMP concentration ([cAMP]i) presumably via activation of protein kinase A. This short term inhibition of protein kinase C-induced adhesion was in contrast to the long term augmentation of adhesion caused by increased [cAMP]i as demonstrated in the companion article. Intercellular adhesion, due to LFA-1/ICAM-1 interactions, could also be induced by LPS treatment of JY cells. At submaximal concentrations, the extent of aggregation induced by LPS had two maxima, one at 30 to 60 min and the other with a plateau at 5 to 8 h. LPS is known to activate protein kinase C and we show that LPS treatment induced increased [cAMP]i. Using inhibitors of protein kinases C and A, possible mediators of the two components of adhesion induced by LPS could be identified. The early component was abrogated by inhibition of protein kinase C although the later component was unaffected. In contrast, an inhibitor of protein kinase A had no affect on the early component and attenuated, but did not entirely eliminate, the late component. These results suggest a model of sequential induction, inhibition, and reinduction of LFA-1/ICAM-1-mediated lymphocyte adhesion that is regulated by temporally ordered actions and interactions of protein kinases C and A.

Lymphocyte adhesion mediated by lymphocyte function-associated antigen-1. II. Interaction between phorbol ester- and cAMP-sensitive pathways

Ag independent adhesion between lymphocytes and target cells is mediated in part by the interaction between lymphocyte function associated Ag-1 (LFA-1) and its coreceptor intercellular adhesion molecule-1 (ICAM-1). Within minutes, PMA treatment of JY cells, which express both LFA-1 and ICAM-1, induced capping of LFA-1 and augmentation of intercellular adhesion lasting for several hours. However, over the course of 15 to 30 min, both of these events were blocked by elevation of intracellular cAMP concentration ([cAMP]i) presumably via activation of protein kinase A. This short term inhibition of protein kinase C-induced adhesion was in contrast to the long term augmentation of adhesion caused by increased [cAMP]i as demonstrated in the companion article. Intercellular adhesion, due to LFA-1/ICAM-1 interactions, could also be induced by LPS treatment of JY cells. At submaximal concentrations, the extent of aggregation induced by LPS had two maxima, one at 30 to 60 min and the other with a plateau at 5 to 8 h. LPS is known to activate protein kinase C and we show that LPS treatment induced increased [cAMP]i. Using inhibitors of protein kinases C and A, possible mediators of the two components of adhesion induced by LPS could be identified. The early component was abrogated by inhibition of protein kinase C although the later component was unaffected. In contrast, an inhibitor of protein kinase A had no affect on the early component and attenuated, but did not entirely eliminate, the late component. These results suggest a model of sequential induction, inhibition, and reinduction of LFA-1/ICAM-1-mediated lymphocyte adhesion that is regulated by temporally ordered actions and interactions of protein kinases C and A.

Lymphocyte adhesion can be regulated by cytoskeleton-associated, PMA-induced capping of surface receptors

Intercellular adhesion in lymphocytes is mediated in part by the interaction of the integrin lymphocyte function-associated antigen-1 (LFA-1) with intercellular adhesion molecule-1 (ICAM-1). The B lymphoblastoid line JY expresses both LFA-1 and ICAM-1, and intercellular adhesion is enhanced by treatment with the phorbol ester phorbol 12-myristate 13-acetate (PMA), which also induced capping of LFA-1, ICAM-1, and human leukocyte antigen. Capping of LFA-1 is likely to result from protein kinase C (PKC) activation because receptor-mediated stimulation of PKC also led to capping. Additionally, adhesion mediated by PMA or lipopolysaccharide was blocked by either of two PKC inhibitors, calphostin C and staurosporine. PMA induced the apparent condensation of cytoskeletal elements that colocalized with the membrane protein cap. Cytoskeletal condensation and capping occurred in the absence of intercellular adhesion. Alteration in the distribution of cytoskeletal components and membrane redistribution of LFA-1 were inhibited by cytochalasin D, which also abolished intercellular adhesion. Taken together, these data suggest that intercellular adhesion is the result of PKC-mediated membrane redistribution of LFA-1 and ICAM-1, which is in turn associated with modification of the actin-based cytoskeleton.

The amelioration of myopia using biofeedback of accommodation: a review

The purpose of this review is to give an account of the issues raised by reports that myopia can be treated by operant conditioning or biological feedback. Devices are available that provide auditory feedback of accommodative state such that variation in tone frequency provides a means by which the patient can monitor his or her ability to induce changes in accommodation response, the task thus being to change the pitch of the tone in a direction corresponding to a more distant far point. The aim of a training programme is to reinforce and establish control over the accommodative response by a process akin to operant conditioning and subsequently to transfer the skill to normal visual environments such that a manifest reduction in myopia becomes apparent. Although there are reports that the technique can induce a reduction in myopia by up to 3 D the findings are of limited value owing to the lack of objective data, for example pre- and post-training cycloplegic refraction. The pre- and post-training measures of subjective letter acuity used by many studies are, with repeated trials, particularly vulnerable to individual differences in the ability to learn how to discriminate and interpret blurred images. The review concludes that more comprehensive clinical trials are needed before accommodation biofeedback can qualify as an established method of clinical treatment of myopia. The trials should be designed to encompass the following issues: the characteristics of a feasible physiological model linking accommodation and myopia development; the rationale with regard to patient selection; the technical performance of the optometer employed; the characteristics of the control group used; the criteria for assessment of myopic change; the transfer of training to performance in normal visual environments; the economic viability of the programme of training and equipment; and the skill, training and knowledge of the clinician implementing the training programme.

Three intracellular signals for cytotoxic T lymphocyte-mediated killing. Independent roles for protein kinase C, Ca2+ influx, and Ca2+ release from internal stores

Ligation of the TCR after interaction of a CTL with a relevant target cell results in a change in CTL shape with reorientation and secretion of cytoplasmic granules. Secretion can be induced by treating CTL with the combination of a phorbol ester to activate protein kinase C and ionomycin to increase the intracellular Ca2+ concentration by ion-selective permeabilization of both the plasma membrane and internal Ca2+ storage depots. Treatment of cloned murine CTL with PMA induced a change in cell shape without movement of cytoplasmic granules, whereas increased intracellular [Ca2+] after treatment with ionomycin resulted in granule movement without shape change. Granule movement induced by ionomycin did not lead to secretion in the absence of PMA. Direct activation of the TCR resulted in increased intracellular Ca2+ predominately from influx of extracellular Ca2+ with a substantially smaller contribution from release of Ca2+ from internal stores. By independently inhibiting either component of the TCR-initiated increase in intracellular Ca2+, it was determined that both sources of Ca2+ were required for granule movement and secretion. Thus, increases in intracellular Ca2+ concentration mediated by these two sources appear not to be functionally equivalent. Taken together, these results indicate that the CTL functional response that normally occurs after interaction with an antigenically relevant target cell is regulated by three independent signals.

Three intracellular signals for cytotoxic T lymphocyte-mediated killing. Independent roles for protein kinase C, Ca2+ influx, and Ca2+ release from internal stores

Ligation of the TCR after interaction of a CTL with a relevant target cell results in a change in CTL shape with reorientation and secretion of cytoplasmic granules. Secretion can be induced by treating CTL with the combination of a phorbol ester to activate protein kinase C and ionomycin to increase the intracellular Ca2+ concentration by ion-selective permeabilization of both the plasma membrane and internal Ca2+ storage depots. Treatment of cloned murine CTL with PMA induced a change in cell shape without movement of cytoplasmic granules, whereas increased intracellular [Ca2+] after treatment with ionomycin resulted in granule movement without shape change. Granule movement induced by ionomycin did not lead to secretion in the absence of PMA. Direct activation of the TCR resulted in increased intracellular Ca2+ predominately from influx of extracellular Ca2+ with a substantially smaller contribution from release of Ca2+ from internal stores. By independently inhibiting either component of the TCR-initiated increase in intracellular Ca2+, it was determined that both sources of Ca2+ were required for granule movement and secretion. Thus, increases in intracellular Ca2+ concentration mediated by these two sources appear not to be functionally equivalent. Taken together, these results indicate that the CTL functional response that normally occurs after interaction with an antigenically relevant target cell is regulated by three independent signals.

Red cell survival studies in a patient with anti-Tca

A radiolabeled, allogenic red cell survival study was performed on a patient who lacked the Cromer-related antigen Tca and who had developed the corresponding antibody. Red cell survival was 92% at 1 hour and 88% at 24 hours. Monocyte monolayer assays (MMA) and IgG subclass determinations were performed on samples from: (1) 1965, the period of initial antibody formation; (2) approximately two years before the red cell survival study; and (3) four months after the study. All samples reacted w+ to 1+ by the antiglobulin test. The earliest sample contained IgG1, IgG2, and IgG4 anti-Tca. Because there were 20.5% reactive monocytes in the MMA (normal range 0-3%), this antibody may have produced extravascular red cell destruction. In contrast to the initial example, the samples before and after the red cell survival study both contained IgG2 and IgG4 subclasses with 1.3% and 2.2% MMA reactivity, respectively. The current pattern of antibody subclass, the lack of reactivity in the MMA, and a red cell survival of 88% at 24 hours indicate that short-term transfusion support would have been well tolerated. This contrasts to the in vitro results obtained with the earliest sample, which suggest a clinically significant antibody. This appears to be the first report of a red cell alloantibody that remained serologically reactive but underwent a loss of its IgG1 fraction, which appeared capable of red cell destruction based on the MMA results.

Multicompartment analysis of the effects of plasmapheresis. Application to lipid kinetics in humans

The quantitative effect of plasmapheresis on concentrations of intravascular solutes is described by a minimal two-compartment model, which allows exit to and entry from a nonplasma body pool of the solute. This novel method is simple and capable of determining endogenous metabolic turnover of physiologically important plasma constituents in both therapeutic and experimental settings. The model was suggested by the therapeutic use of plasmapheresis in hyperlipidemia, and the turnover rates of triglyceride and cholesterol were calculated for one patient treated with chronic plasmapheresis. It is concluded that at least a two-compartment model is necessary to quantitatively describe the effect of plasmapheresis on any substance that undergoes appreciable endogenous turnover (metabolic clearance rate greater than 1.1 times plasmapheresis rate when both rates are in units of volume per time). Calculation of endogenous turnover rate with the use of measurements of the concentration of a solute in plasma before and after plasmapheresis and in the total plasmapheresate and measurement of the volume of plasma removed, volume of plasma substitute infused, and total plasmapheresis time is detailed. This method avoids the use of isotopic labeling experiments. In turn, the endogenous turnover rate may predict the efficacy of therapeutic plasmapheresis.

Pertussis toxin effects on T lymphocytes are mediated through CD3 and not by pertussis toxin catalyzed modification of a G protein

Pertussis toxin (PT) has been shown to have a variety of effects on T lymphocyte function, and its activity has been used to suggest the involvement of a G protein in the early events of T lymphocyte activation. In this report, the effects of PT on T lymphocytes have been investigated in detail. PT at a concentration of 10 micrograms/ml rapidly stimulated early events that are normally induced by occupancy of the TCR complex in Jurkat cells and cloned, murine CTL including increased intracellular Ca2+ concentration, serine esterase release, and induction of Ag non-specific target cell lysis. However, 1-h treatment with this concentration of PT induced a state that was refractory to further receptor stimulation in Jurkat cells but not cloned CTL although substrate membrane proteins were modified to a similar extent in both cell lines. The functional effects of PT were mimicked by the B oligomer of PT which did not, however, catalyze ADP-ribosylation of membrane proteins. In addition, overnight exposure of Jurkat cells to a lower concentration of PT also modified substrate membrane proteins but did not inhibit receptor stimulation. These findings indicate that PT catalyzed ADP-ribosylation of a G protein does not account for the actions of the toxin on T lymphocytes. Finally, direct stimulation of increased intracellular Ca2+ concentration by PT and the B oligomer only occurred in T lymphocytes expressing CD3. This suggests that the mitogenic effect of PT holotoxin is mediated by the interaction of the B oligomer with CD3 and that this may account for many of the effects of PT holotoxin both in vivo and in vitro.

Pertussis toxin effects on T lymphocytes are mediated through CD3 and not by pertussis toxin catalyzed modification of a G protein

Pertussis toxin (PT) has been shown to have a variety of effects on T lymphocyte function, and its activity has been used to suggest the involvement of a G protein in the early events of T lymphocyte activation. In this report, the effects of PT on T lymphocytes have been investigated in detail. PT at a concentration of 10 micrograms/ml rapidly stimulated early events that are normally induced by occupancy of the TCR complex in Jurkat cells and cloned, murine CTL including increased intracellular Ca2+ concentration, serine esterase release, and induction of Ag non-specific target cell lysis. However, 1-h treatment with this concentration of PT induced a state that was refractory to further receptor stimulation in Jurkat cells but not cloned CTL although substrate membrane proteins were modified to a similar extent in both cell lines. The functional effects of PT were mimicked by the B oligomer of PT which did not, however, catalyze ADP-ribosylation of membrane proteins. In addition, overnight exposure of Jurkat cells to a lower concentration of PT also modified substrate membrane proteins but did not inhibit receptor stimulation. These findings indicate that PT catalyzed ADP-ribosylation of a G protein does not account for the actions of the toxin on T lymphocytes. Finally, direct stimulation of increased intracellular Ca2+ concentration by PT and the B oligomer only occurred in T lymphocytes expressing CD3. This suggests that the mitogenic effect of PT holotoxin is mediated by the interaction of the B oligomer with CD3 and that this may account for many of the effects of PT holotoxin both in vivo and in vitro.

Spatial and temporal characteristics of the increase in intracellular Ca2+ induced in cytotoxic T lymphocytes by cellular antigen

The increase in intracellular Ca2+ concentration [( Ca2+]i) in cytolytic T lymphocytes in response to target cell binding was investigated by ratio image fluorescence microscopy. Ca2+ mobilization from intracellular stores occurred at a site distal to target cell contact and was transient. Extracellular Ca2+ influx resulted in an increase in [Ca2+]i that was prolonged and distributed more proximal to the target cell. Oscillations in [Ca2+]i were observed after target cell contact, although the periodicity was dependent on the presence of extracellular Ca2+. The Ag-specific reorientation of cytoplasmic granules occurred well after [Ca2+]i had begun to decline to a resting level, but was dependent on extracellular Ca2+. These studies indicate that the Ag-stimulated increase in [Ca2+]i exhibits considerable spatial and temporal variation, and that these characteristics are altered by the availability of extracellular Ca2+. The results also suggest that these changes in [Ca2+]i may play a role in the cytoplasmic events that accompany T cell-mediated cytolysis.