On Peptides and Altered Peptide Ligands: From Origin, Mode of Action and Design to Clinical Application (Immunotherapy)

T lymphocytes equipped with clonotypic T cell antigen receptors (TCR) recognize immunogenic peptides only when presented in the context of their own major histocompatibility complex (MHC) molecules. Peptide loading to MHC molecules occurs in intracellular compartments (ER for class I and MIIC for class II molecules) and relies on the interaction of the respective peptides and peptide binding pockets on MHC molecules. Those peptide residues not engaged in MHC binding point towards the TCR screening for possible peptide MHC complex binding partners. Natural or intentional modification of both MHC binding registers and TCR interacting residues of peptides – leading to the formation of altered peptide ligands (APLs) – might alter the way peptides interact with TCRs and hence influence subsequent T cell activation events, and consequently T cell effector functions. This review article summarizes how APLs were detected and first described, current concepts of how APLs modify T cellular signaling, which biological mechanisms might force the generation of APLs in vivo, and how peptides and APLs might be used for the benefit of patients suffering from allergic or autoimmune diseases.

Basilar and middle cerebral artery reserve: a comparative study using transcranial Doppler and breath-holding techniques

BACKGROUND AND PURPOSE

A 1997 report suggests that the posterior circulation of the normal brain has diminished vasoreactivity compared with the anterior circulation. To further study this, we quantified and compared the vasodilatory capacities of the middle cerebral (MCA) and basilar artery (BA) territories in response to changes in PaCO(2), as indices of respective cerebrovascular reserve (CVR). If posterior circulation CVR is indeed physiologically lower than that of the MCA, it might indicate a greater risk of low-flow ischemia distal to basilar obstructive cerebrovascular lesions and provide a rationale for earlier treatment of such lesions with interventional techniques. We also wished to establish normal baseline CVR values for the posterior circulation.

METHODS

Twelve patients with signs and/or symptoms suggestive of posterior circulation disease but without flow-limiting obstructive changes and 11 normal controls were entered into the study. With the use of transcranial Doppler techniques, alterations in blood flow velocity in response to sequential breath-holding trials of varying duration were simultaneously monitored in both MCAs and the BA. CVR was measured as the percent velocity increase (during breath-holding) from resting baseline values.

RESULTS

No significant differences were found in CVR between the MCA and BA territories in or between patients and controls.

CONCLUSIONS

Our study suggests that the anterior and posterior circulations have similar reserve capacities in individuals without flow-limiting cerebrovascular obstructive lesions and that the BA territory, relative to the MCA territory, is not at increased risk for low-flow stroke on the basis of limited reserve potential.

[Evaluation of acute effect of GnRH administration on leptin secretion in normal and hyperandrogenic women]

BACKGROUND

Several studies suggest that leptin modulates the reproductive axis function. Leptin may stimulate release of GnRH from hypothalamus and of gonadotrophins from the pituitary. A synchronicity of LH and leptin pulses has been described in healthy women and in patients with polycystic ovarian syndrome (PCOS), suggesting a relationship between the episodic secretion of LH and leptin. In vitro experimental studies have demonstrated that leptin administration promotes GnRH-LH release. However it is not established whether GnRH promotes the episodic secretion of leptin.

AIM

To assess the response of LH and leptin to the administration of a GnRH bolus in hyperandrogenic and healthy women.

PATIENTS AND METHODS

Eleven hyperandrogenic and eleven healthy women of similar age and body mass index (BMI) were studied. Under basal conditions three blood samples were collected every 30 min before and after the administration of a GnRH bolus (100 micrograms). LH and leptin concentrations were measured in all samples. Testosterone, SHBG and estradiol were determined in the first sample. For data analysis, the increment of LH and leptin between 0-30 and 0-60 min was calculated. The LH and leptin areas under the curve (AUC) before and after GnRH administration were also calculated in both groups.

RESULTS

After GnRH administration an increment in LH concentrations was observed in both groups; however, leptin concentrations were not modified. In both groups LH area under the curve increased after GnRH administration; however, the leptin area was not modified.

CONCLUSIONS

These results suggest that circulating leptin concentration is not modulated by GnRH-LH.

Gadolinium-enhanced MR angiography of the carotid arteries

To assess the efficacy of gadolinium (Gd)-enhanced magnetic resonance angiography (gdMRA) in overcoming signal dropout artifacts on conventional MRA (cMRA), the authors examined 13 patients with suspected neurovascular stenotic/occlusive lesions on MRA pre- and post-gadolinium enhancement. The sample consisted of 18 internal carotid artery (ICA) les ons (16 extracranial, 2 cranial). In 13 of 16 stenotic vessels, gdMRA better characterized the pathoanatomy of moderate to severe stenotic lesions, changing MRA diagnosis in 3 patients. In zero of three vessels with no flow enhancement by cMRA, the lumen remained nonvisualized on gdMRA. For an ICA lesion at the skull base, enhancement of surrounding normal structures limited the usefulness of the technique. The authors conclude that Gd MRA is a fast, accurate, and convenient noninvasive technique for documenting the morphology and severity of carotid stenotic disease, especially extracranially.

[Insulin tolerance test. A useful test to determine insulin resistance in obese hyperandrogenic women]

BACKGROUND

Insulin tolerance test is a simple method to measure insulin resistance that has a good correlation with glucose clamp studies.

AIM

To use the insulin tolerance test to detect differences in insulin sensitivity between healthy and obese hyperandrogenic women and to correlate its results with those of the minimal model intravenous glucose tolerance test.

PATIENTS AND METHODS

Five healthy women aged 27 +/- 7 years old with a body mass index of 21 +/- 2 kg/m2 and six hyperandrogenic women aged 25 +/- 4 years old with a body mass index of 40 +/- 5 kg/m2 were studied after a 10 hours fast. For the insulin tolerance test 0.1 U/kg of crystalline insulin were injected intravenously and blood samples were drawn to measure glucose at -5,0,3,5,10 and 15 min. after the injection. Insulin resistance was calculated using the slope of descending blood glucose levels (SI1). For the intravenous glucose tolerance test, 29 blood glucose samples were obtained after an intravenous injection of 0.3 g glucose/kg followed by an injection of 0.02 U/kg of crystalline insulin. Insulin sensitivity (SI2) was calculated using Bergman's minimal model.

RESULTS

Healthy women had a SI1 of 0.58 (range 0.53-0.63) and a SI2 of 7.9 x 10(-4) x min-1/microU/ml (range 4.15-9.11). For hyperandrogenic women were 0.18 (range 0.06-0.29) and 0.9 x 10(-4) x min-1/microU/ml (range 0.46-1.79), respectively. Both methods had a positive correlation coefficient of 0.859 (p < 0.001).

CONCLUSIONS

Insulin tolerance test is a good method to measure insulin resistance and has a good correlation with the frequently sampled intravenous glucose tolerance test.

Reduced incidence of cerebral ischemia following rupture of intracranial aneurysms

A randomized study was carried out to determine if the administration of reserpine and kanamycin to lower the concentration of vasoactive biogenic monoamines would reduce the incidence of cerebral vascular ischemic complications and death following the rupture of intracranial aneurysms. Twenty-six treated and twenty-eight control (untreated) patients were studied. In the preoperative period, eight control (untreated) patients developed symptomatic cerebral ischemia as opposed to one treated patient. There was no correlation between the preoperative clinical findings of ischemia and angiographic evidence of vasospasm. In the post-operative period four control and one treated patient developed symptomatic cerebral ischemia; vasospasm, as demonstrated by cerebral angiography, paralleled these findings.