Factors controlling the trafficking and processing of a leader-derived peptide presented by Qa-1.

Many leader-derived peptides require TAP for presentation by class I molecules. This TAP dependence can either be ascribed to the inability of proteases resident in the endoplasmic reticulum (ER) to trim leader peptide precursors into the appropriate epitope or the failure of a portion of the leader segment to gain access to the lumen of the ER. Using the Qa-1 binding epitope, Qdm derived from a class Ia leader as a model, we show that many cell types lack ER protease activity to trim this peptide at its C terminus. However, both T1 and T2 cells contain appropriate protease activity to process the full length D(d) leader (DL) when introduced into the ER lumen. Nevertheless, both T1 cells treated with the TAP inhibitor ICP47 and TAP(-) T2 cells fail to present this epitope from either the intact D(d) molecule or a minigene encoding the DL. This indicates that the portion of the leader containing Qdm does not gain access to the ER. However, changing the Arg at P7 of the DL to a Cys can alter its trafficking and allows for TAP-independent presentation of the Qdm epitope.

Management of diabetic pregnancies in the United Kingdom.

The aim of this postal questionnaire survey was to identify facilities currently available for the care of pregnant diabetic women in the United Kingdom and determine how closely these reflect the standards recommended by The St Vincent Declaration Action Programme. A questionnaire was sent to a physician and an obstetrician in each of the 255 obstetric hospitals in the UK. Two hundred and forty-five (96.1%) hospitals replied, with most of these managing 20 or less insulin dependent diabetics per year. Of the hospitals, 58.4%, had a special combined diabetic antenatal clinic; 86.6% of the units had a single physician responsible for diabetic care, whilst more than one obstetrician was involved in 50.6% of the units. Prepregnancy counselling was provided in 87.4% of the hospitals. Home blood glucose monitoring was used in 97.9% of the units. Ideal mean pre- and postprandial blood glucose concentrations were 6.0 mmol/1 (SD 0.82) and 7.9 mmol/l (SD 0.91), respectively. Ultrasound was routinely used to assess fetal growth in 98.7% of the units. The mean gestational age for elective caesarean section was 38.2 weeks (SD 0.55), compared with 39.0 weeks (SD 0.35) for planned vaginal delivery. During labour, 98% of the units used a dextrose and insulin infusion, but only 53.7% of the units maintained an intrapartum maternal blood glucose of between 4 and 6 mmol/l. We conclude that there is widespread variation in the management of the pregnant diabetic patient, and much practice is suboptimal. Many of the recommendations of the St Vincent Declaration are not being met by current UK practice.

Screening for gestational diabetes in the United Kingdom: a national survey.

To determine the attitudes of British obstetricians to screening for gestational diabetes a postal questionnaire survey was undertaken. A questionnaire was sent to a single obstetrician in each of 255 obstetric hospitals identified in the United Kingdom. Of the 189 (75%) units that replied, only 42.3% had a protocol for screening for gestational diabetes. Routine antenatal screening was performed by urinalysis and blood glucose tests in 89.4% and 32.8% of units respectively. Clinical risk factors were used as an indication for routine blood glucose testing in 91.5% units. Following a positive screening test 54.5% of units performed a 75 g oral glucose tolerance test (GTT) and of these 64% relied on the World Health Organisation diagnostic criteria to interpret the result. There currently appears to be widespread variation in the practice of screening for gestational diabetes in the United Kingdom.

Constitutive and regulated expression of the class IB molecule Qa-1 in pancreatic beta cells.

Enhanced major histocompatibility complex (MHC) class I expression is a prominent early feature of pancreatic beta-cell pathology in autoimmune diabetes. The number and nature of class I MHC loci expressed by beta cells are generally undefined and potentially critical to the onset and progression of insulitis. Mounting evidence indicates that the non-classical MHC class IB molecule Qa-1, encoded by H2-T23, is capable of presenting antigens to alpha beta and gamma delta T cells and that lymphocytes restricted to Qa-1 may contribute immunoregulatory functions. We compared the expression of Qa-1 and MHC class IA in a beta-cell line (beta TC6-F7) before and after treatment with the insulitic cytokine interferon-gamma (IFN-gamma). Similar to MHC class IA, Qa-1 was expressed constitutively at a low level in beta TC6-F7 cells, with both T23b mRNA and cell surface Qa-1b being up-regulated following 24-hr treatment with mouse IFN-gamma. Based on binding characteristics established for the predominant Qa-1-binding peptide, Qa-1 determinant modifier (Qdm), we also examined the possibility that Qa-1 binding peptides may be encoded in the preproinsulin leader sequence. One nonarmeric peptide (Ins II: ALWMRFLPL) derived from the preproinsulin II leader sequence was recognized by a Qa-1b-specific cytotoxic T-lymphocyte (CTL) clone. Specific binding of Ins II to Qa-1b was confirmed by a CTL peptide-blocking assay. Demonstration of IFN-gamma-regulated Qa-1 expression in beta cells and identification of a Qa-1-binding peptide in the preproinsulin leader sequence invoke further consideration of possible roles of Qa-1 in the progression of islet inflammation.

Increased class Ib antigen display on TAP-2 mutant cells by a mitochondrial function inhibitor.

Class I histocompatibility antigen display is defective in the RMA-S mutant cell line due to a mutation in the Tap-2 gene, which encodes a peptide transporter. Incubation of RMA-S cells with oligomycin, an inhibitor of mitochondrial ATPase, strongly increased lysis by cytotoxic T lymphocytes (CTL) specific for the class Ib antigen H2-M3, and lysis by Qa-1b-specific CTL was restored. Oligomycin did not affect normal class I display on RMA cells. Treatment of RMA-S cells with other inhibitors of mitochondrial function failed to increase lysis by anti-H2-M3 or Qa-1b CTL. Lysis by allogenic CTL specific for H-2b antigens was either not enhanced or only weakly increased, depending upon the H-2 haplotype of the alloreactive effector cells used.

Fetal heart rate changes and cerebral oxygenation measured by near-infrared spectroscopy during the first stage of labour.

OBJECTIVE: To determine the relationship between contraction related changes in fetal heart rate and cerebral oxygenation measured by near-infrared spectroscopy during labour. STUDY DESIGN: A specially designed optical probe was inserted through the dilated cervix and placed against the fetal head in 30 women during labour. Alterations in fetal heart rate during the final hour of the first stage of labour were compared with changes in the cerebral haemoglobin oxygenation index (delta oxyhaemoglobin concentration - delta deoxyhaemoglobin concentration) measured before, during and after uterine contractions. RESULTS: Uterine contractions which were associated with either no alteration, accelerations or early decelerations of the fetal heart rate showed no significant changes in the haemoglobin oxygenation index. Variable, late and prolonged decelerations all showed significant decreases in the haemoglobin oxygenation index (P < 0.01) either during (variable) or after (variable, late and prolonged) the uterine contraction. CONCLUSION: The association between variable, late and prolonged FHR decelerations and significant falls in cerebral oxygenation during late labour suggests that these fetal heart rate patterns are associated with an increased risk of fetal cerebral hypoxia.

The effect of maternal pushing on fetal cerebral oxygenation and blood volume during the second stage of labour.

OBJECTIVE: To measure the effect of maternal pushing during the second stage of labour on fetal cerebral oxygenation and blood volume. DESIGN: A prospective study comparing changes in the fetal cerebral concentrations of oxyhaemoglobin, deoxyhaemoglobin and cerebral blood volume, before and during maternal pushing in the second stage of labour. SETTING: Teaching hospital obstetric unit. SUBJECTS: Ten term fetuses during labour. RESULTS: Following the onset of maternal pushing, mean cerebral deoxyhaemoglobin concentration increased by a mean of 0.79 (SD 0.59) mumol.100 g-1, (P < 0.01) without any consistent change in the oxyhaemoglobin concentration. These changes were associated with a significant decrease in the calculated mean cerebral oxygen saturation from a mean of 46.8% (SD 8.6) to 38.1% (SD 5.2) (P < 0.01). Pushing was also associated with a significant increase in the mean cerebral blood volume, which rose by a mean of 0.33 ml.100 g-1 (SD 0.37) (P < 0.05). CONCLUSION: Maternal pushing during the second stage of labour leads to a significant decrease in fetal cerebral oxygenation, together with an increase in cerebral blood volume.

Effect of nuchal cord on fetal cerebral haemodynamics and oxygenation measured by near infrared spectroscopy during labour.

OBJECTIVE: To test the hypothesis that a nuchal cord has a significant effect upon fetal cerebral haemodynamics and oxygenation during labour. STUDY DESIGN: A specially designed optical probe was inserted through the dilated cervix and placed against the scalp of 37 fetuses during labour in a teaching hospital obstetric unit. Changes in total cerebral haemoglobin concentration were measured continuously together with fetal heart rate and uterine contraction frequency during the first and second stages. RESULTS: At birth 11 fetuses (30%) were noted to have a nuchal cord (cord around the neck). For these, significantly more contractions were associated with an increase in total cerebral haemoglobin concentration when compared with the control fetuses without a nuchal cord (40.2% (S.D.19.5) vs 5.9% (S.D.7.1), P < 0.001). A significantly greater number of variable decelerations was found in the nuchal cord group (4 per 30 min vs. 2 per 30 min in the controls) (P < 0.01). There was no significant difference between mean cerebral oxygen saturation determined at the end of the first stage of labour, which was 47.0% (S.D.13.3) and 50.1% (S.D.11.8) for the nuchal cord and control groups, respectively. CONCLUSION: A nuchal cord was associated with a significant increase in cerebral blood volume during uterine contractions, without any significant effect upon cerebral oxygenation.

The effect of maternal posture on fetal cerebral oxygenation during labour.

OBJECTIVE: To measure the effect of changes in maternal posture on fetal cerebral oxygenation during normal labour. DESIGN: A prospective study comparing changes in the fetal cerebral concentrations of oxyhaemoglobin, deoxyhaemoglobin and cerebral blood volume, measured by near infrared spectroscopy, in women with effective epidural analgesia when moved from the left lateral to the supine position during labour. SETTING: A London teaching hospital obstetric unit. SUBJECTS: Fourteen women during uncomplicated labour at term. RESULTS: When compared with the left lateral position, the supine position was associated with a significant decrease in the mean concentration of fetal cerebral oxyhaemoglobin of 1.12 (SD 1.0, 95% CI 0.49 to 1.75) mumol. 100 g-1 (P < 0.01) without any significant change in the mean concentration of deoxyhaemoglobin and cerebral blood volume. These changes were associated with a significant decrease in the mean cerebral oxygen saturation of 8.3 (SD 8.8, 95% CI 1.5 to 15.1)% (P < 0.05, n = 9). CONCLUSION: Changes in maternal posture during labour, in women with effective epidural analgesia, are associated with a significant decrease in fetal cerebral oxygenation.

Late fetal heart decelerations and changes in cerebral oxygenation during the first stage of labour.

OBJECTIVE: To test the hypothesis that late fetal heart rate decelerations are associated with a decrease in cerebral oxygenation. DESIGN: Changes in fetal cerebral concentrations of oxyhaemoglobin and deoxyhaemoglobin were measured by near infrared spectroscopy, before, during and after contractions with late fetal heart rate decelerations and compared with changes during contractions with no alteration of heart rate. SETTING: Teaching hospital obstetric unit. SUBJECTS: Ten women in labour at term. RESULTS: The changes in fetal cerebral oxyhaemoglobin and deoxyhaemoglobin concentrations that occurred during contractions were quantitatively similar, irrespective of the fetal heart rate changes. However, late fetal heart rate decelerations were associated with a significantly greater fall, after the uterine contraction, in the mean concentration of fetal cerebral oxyhaemoglobin of 0.52 mumol/100 g (SD 0.25) (P < 0.001) and a significantly greater rise in the mean concentration of deoxyhaemoglobin of 0.36 mumol/100 g (SD 0.35) (P < 0.01). CONCLUSION: Late fetal heart rate decelerations are associated with a significant decrease in cerebral oxygenation.

Identification of a Tap-dependent leader peptide recognized by alloreactive T cells specific for a class Ib antigen.

Recognition of the class Ib antigen Qa-1 by a portion of alloreactive cytotoxic T lymphocyte (CTL) clones requires that the target cell express a second gene, termed Qa-1 determinant modifier (Qdm). We show that Qdm is identical to most D allele genes, excepting Dk, and that a nonamer peptide derived from D alloantigens restores CTL recognition on cells that lack the Qdm-encoded determinant. The equivalent Dk peptide has an Ala-->Val interchange at P3 and requires approximately 4 logs more peptide than the AlaP3 peptide for target cell lysis. Two of five CTL clones, not dependent on Qdm for target cell recognition, also recognize the Qdm peptide as well as the ValP3 variant. Although the Qdm peptide spans residues 3-11 from the leader, it requires the Tap transporters for its expression. Thus, the response against this class Ib molecule provides a tool for dissecting alloreactivity as well as pathways for antigen presentation.

Fetal cerebral oxygenation measured by near-infrared spectroscopy shortly before birth and acid-base status at birth.

OBJECTIVE: To test the hypothesis that the mean cerebral oxygen saturation measured by near-infrared spectroscopy shortly before delivery correlates with fetal acid-base status in umbilical cord blood. METHODS: A specially designed optical probe was inserted through the dilated cervix and placed against the fetal head during labor in 41 women. Changes in cerebral oxyhemoglobin and deoxyhemoglobin concentrations were measured continuously, and the mean cerebral oxygen saturation was determined over a 10-minute period within 30 minutes of delivery. Umbilical arterial and venous blood acid-base status was assessed immediately after birth and then correlated to the values for mean cerebral saturation. RESULTS: Values for mean cerebral oxygen saturation could be determined in 33 fetuses. Umbilical cord artery and vein pH (r = 0.82 and r = 0.79, respectively) showed significant positive correlations (P < .001), whereas base deficit (r = -0.73 and r = -0.71) and carbon dioxide pressure (r = -0.68 and r = -0.63) showed significant negative correlations (P < .001) with mean cerebral oxygen saturation measured within 30 minutes before birth. There was also a significant positive correlation between umbilical vein oxygen pressure and mean cerebral oxygen saturation (r = 0.51, P < .01). CONCLUSION: Fetal umbilical blood gas and acid-base status at birth showed significant correlations with mean cerebral oxygen saturation measured shortly before delivery. Low values for saturation were related to both respiratory and metabolic acidemia.

Positive selection of self- and alloreactive CD8+ T cells in Tap-1 mutant mice.

Mice with a homozygous deletion in their Tap-1 gene (-/- mice) express very low levels of cell membrane major histocompatibility complex class I molecules and have < 1% peripheral CD8+ T cells. We show that these -/- mice but not their +/- littermates display strong primary syngeneic anti-H-2Kb and -Db-specific responses mediated by CD8+ T cells. These responses are augmented by in vivo priming. Further, -/- mice primed in vivo with H-2d alloantigens generate an anti-H-2d response which appears nearly as strong as that found in +/- littermates. Both -/- anti-H-2b and anti-H-2d T cells do not recognize target cells from Tap-1 -/- animals or Tap-2-deficient RMA-S cells. Thus, some CD8+ anti-self and alloreactive T cells can be selected in the absence of Tap proteins.

The effect of maternal oxygen administration on human fetal cerebral oxygenation measured during labour by near infrared spectroscopy.

OBJECTIVE: To test the hypothesis that intrapartum maternal oxygen administration increases fetal cerebral oxygenation during normal labour. DESIGN: A prospective study comparing changes in fetal cerebral concentrations of oxyhaemoglobin, deoxyhaemoglobin and cerebral blood volume measured by near infrared spectroscopy, before, during and after maternal oxygen administration using a 60% Ventimask. SETTING: Teaching hospital obstetric unit. SUBJECTS: Ten term fetuses during uncomplicated labour. RESULTS: Maternal oxygen administration for 15 min resulted in a significant increase in the mean concentration of fetal cerebral oxyhaemoglobin (0.78 mumol (SD 0.42) 100 g-1 brain tissue, P < 0.001) and a significant decrease in the mean concentration of deoxyhaemoglobin (0.80 mumol (SD 0.51) 100 g-1, P < 0.001). These changes were associated with a significant increase in the calculated mean cerebral oxygen saturation from 43.9% (SD 6.3) to 57.3% (SD 5.6) (P < 0.001). The maximum rise in cerebral oxyhaemoglobin concentration occurred at a mean of 10.7 min (SD 3.9) following commencement of oxygen administration. On returning to air breathing these changes reversed. There were no changes in cerebral blood volume. CONCLUSION: Maternal oxygen administration during normal labour leads to a significant rise in fetal cerebral oxygenation.