The validity of eye blink rate in Chinese adults for the diagnosis of Parkinson's disease

We evaluated the eye blink rate (EBR) in healthy Chinese adults and Parkinson's disease (PD) patients. In healthy subjects, the EBR declined with age, was lower in women than men younger than 50 years of age, and did not differ from male PD patients older than 60 years or female PD patients older than 50 years. Accordingly, EBR is not a good indicator for bradykinesia in Chinese individual older than 50 years that is prevalent for PD onset also.

Failure of central 5-hydroxytryptamine depletion to alter the effect of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on timing performance on the free-operant psychophysical procedure

RATIONALE

The 5-hydroxytryptamine (5-HT)(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) alters temporal differentiation of behaviour on the free-operant psychophysical procedure, displacing the psychophysical curve to the left, thereby reducing the indifference point T(50). However, it is not known whether this effect of 8-OH-DPAT is mediated by an action of the drug at somatodendritic autoreceptors or at postsynaptic receptors.

OBJECTIVE

To compare the effects of 8-OH-DPAT on performance on the free-operant psychophysical procedure in normal (sham-lesioned) rats and in rats whose 5-HTergic pathways had been lesioned by means of intra-raphe injections of the selective neurotoxin 5,7-dihydroxytryptamine (5,7-DHT).

METHODS

Twelve rats received 5,7-DHT-induced lesions of the median and dorsal raphe nuclei, and twelve received sham lesions. They were trained under the free-operant psychophysical procedure to press two levers (A and B) in 50-s trials, during which reinforcement was provided intermittently for responding on A in the first half and B in the second half of the trial. Percentage responding on B (%B) was recorded in successive 5-s epochs of the trials; logistic psychophysical curves were fitted to the data from each rat for the derivation of timing indices [T(50) (time corresponding to %B=50%) and Weber fraction] following treatment with acute doses of 8-OH-DPAT (25, 50, 100, 200 microg kg(-1), s.c.) and saline (vehicle-alone treatment). Levels of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), noradrenaline and dopamine were measured in forebrain regions after the completion of the experiment.

RESULTS

Under the vehicle-alone condition, the lesioned group displayed a greater propensity for switching between the levers, but T(50) and the Weber fraction did not differ between the groups. In both groups, 8-OH-DPAT shifted the psychophysical curve to the left, significantly reducing T(50) at the 200-microg kg(-1) dose; the effect of 8-OH-DPAT did not differ significantly between the groups. Levels of 5-HT and 5-HIAA in the lesioned group were about 10% of those in the sham-lesioned group; there was no effect of the lesion on catecholamine levels.

CONCLUSIONS

The results confirm that 8-OH-DPAT disrupts temporal differentiation in the free-operant psychophysical schedule, reducing the indifference time, T(50). The failure of central 5-HT depletion to alter the effect of 8-OH-DPAT suggests that this effect may be mediated by stimulation of postsynaptic 5-HT(1A) (or possibly 5-HT(7)) receptors rather than somatodendritic 5-HT(1A) autoreceptors.

Effects of central 5-hydroxytryptamine depletion on sensitivity to delayed and probabilistic reinforcement

RATIONALE

The ascending 5-hydroxytryptaminergic (5-HTergic) pathways are believed to be involved in "impulse control". Rats whose 5-HTergic pathways have been destroyed are more liable than intact rats to select a smaller, immediate reinforcer rather than a larger, delayed reinforcer (impulsive choice), and recent evidence indicates that this effect of central 5-HT depletion reflects a change in the rate of time discounting (i.e. a change in the rate at which reinforcers become devalued as a function of delay). Delay of reinforcement and uncertainty of reinforcer delivery are believed to have equivalent effects on choice behaviour. However, it is not known whether central 5-HT depletion affects choice between probabilistic reinforcers.

OBJECTIVE

We examined the effects of central 5-HT depletion on choice behaviour in two experiments: In experiment 1, rats chose between a smaller immediate reinforcer and a larger delayed reinforcer; in experiment 2, rats chose between a smaller certain reinforcer and a larger probabilistic reinforcer.

METHODS

Rats received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei or sham lesions. They were trained to press two levers for food-pellet reinforcers in discrete-trials schedules. In free-choice trials, selection of lever A resulted in immediate delivery of one food pellet; selection of lever B resulted in delivery of 2 pellets, either following a delay (dB) (experiment 1) or with a probability (pB) less than 1 (experiment 2).

RESULTS

In experiment 1, both groups showed declining choice of lever B (%B) as a function of dB. The lesioned group showed shorter indifference delays (D50: the value of dB corresponding to %B=50) than the sham-lesioned group. In experiment 2, both groups showed declining choice of lever B as a function of the odds against delivery of the two-pellet reinforcer, thetaB (thetaB=[1/pB]-1). There was no difference between the "indifference odds" (theta50: the value of thetaB corresponding to %B=50) between the two groups. In both experiments, the levels of 5-HT and 5-hydroxyindoleacetic acid were reduced in the brains of the lesioned rats, but the levels of noradrenaline and dopamine were not altered.

CONCLUSIONS

These results provide additional evidence that central 5-HTergic mechanisms are involved in time discounting, but provide no evidence for a similar role of 5-HT in rats' sensitivity to probabilistic reinforcement.

Effects of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on performance on two operant timing schedules

RATIONALE

Previous experiments have shown that the disruptive effect of central 5-HT depletion on interval timing behaviour is critically dependent upon the particular timing schedule used. However, it is not known how acute disruption of 5-HTergic function brought about by drugs acting at 5-HT receptors affects timing.

OBJECTIVE

To examine the effects of the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) on performance on two quantitative timing schedules, a free-operant schedule in which rats were trained to distribute their responses differentially between two levers during the course of a 50-s trial (free-operant psychophysical procedure) and a discrete-trials schedule in which rats were trained to discriminate the durations of light stimuli (interval bisection task).

METHODS

In experiment 1, rats were trained under the free-operant psychophysical procedure to respond on two levers (A and B) in 50-s trials in which reinforcement was provided intermittently for responding on A in the first half, and B in the second half, of the trial. For one group, repetitive switching between levers was permitted; for another group, it was prevented. In experiment 2, rats were trained to press lever A after a 2-s stimulus and lever B after an 8-s stimulus, and were then tested with stimuli of intermediate durations. For one group, a 'poke response' (depression of a central tray flap) was required after stimulus presentation to effect lever presentation; for the other group this requirement did not operate. In both experiments, quantitative indices of timing were derived from the psychophysical functions (%B responding vs time).

RESULTS

In experiment 1, 8-OH-DPAT (25, 50, 100 and 200 microg kg(-1) s.c.) displaced the psychophysical curve to the left in both versions of the schedule. In experiment 2, 8-OH-DPAT increased the Weber fraction in both versions of the task without displacing the curve.

CONCLUSIONS

These results show that 8-OH-DPAT disrupts timing behaviour. The results of experiment 1 are consistent with the proposal that 5-HTergic mechanisms help to regulate the period of the hypothetical pacemaker. However, the results of experiment 2 do not support this suggestion. Taken together, the results support the notion that different neural mechanisms may be involved in timing tasks involving temporal distribution of responding and discrimination of the durations of exteroceptive stimuli.

Comparison of the effects of clozapine, haloperidol, chlorpromazine and d-amphetamine on performance on a time-constrained progressive ratio schedule and on locomotor behaviour in the rat

Performance on progressive ratio schedules has been proposed as a means of assessing the effects of drugs on "reinforcer efficacy". It has been proposed that the effects of neuroleptic drugs on operant behaviour are mediated by a reduction of "reinforcer efficacy". We examined the effects of two "conventional" neuroleptics (haloperidol and chlorpromazine) and an "atypical" neuroleptic (clozapine) on progressive ratio schedule performance; d-amphetamine was used as a comparison compound. In experiment 1, rats responded for a sucrose reinforcer on a time-constrained progressive ratio schedule (75-min sessions). After 66 preliminary training sessions, the rats received single doses (IP) of haloperidol (0.05, 0.1 mg kg(-1)). chlorpromazine (2, 4 mg kg(-1)), clozapine (0.5, 1, 2, 4, 8 mg kg(-1)), and d-amphetamine (0.2, 0.4, 0.8 mg kg(-1)), and the corresponding vehicle solutions. The highest ratio completed was reduced by haloperidol and chlorpromazine, and increased by clozapine. All three neuroleptics reduced the peak response rate, at least at the highest doses administered. Response rates on the lower and intermediate ratios could be described by a three-parameter equation proposed to account for fixed ratio schedule performance. Haloperidol reduced, and clozapine dose-dependently increased the "motivational" parameter (a); d-amphetamine reduced it at low doses and increased it at high doses. The three neuroleptics increased the "response time" parameter (delta). Un-reinforced locomotor behaviour, measured in experiment 2, was not significantly altered by haloperidol, chlorpromazine or clozapine, but was increased by d-amphetamine. These results are consistent with a reduction of reinforcer efficacy produced by haloperidol and an increase produced by clozapine; clozapine's effect is unlikely to reflect a general increase in locomotion. All three neuroleptics induced some degree of motor debilitation. The quantitative analysis of progressive ratio schedule performance may provide a useful adjunct to existing methods for separating effects of drugs on motivational and motor processes.

The effect of d-amphetamine on performance on two operant timing schedules

RATIONALE

Previous experiments have shown that d-amphetamine disrupts timing behaviour in rats. It has been proposed that d-amphetamine's effects reflect a reduction in the period of the pacemaker of the hypothetical internal clock. However, some studies have obtained conflicting results.

OBJECTIVE

To examine the effects of d-amphetamine (0.2, 0.4, 0.8 mg kg(-1) i.p.) on performance on two quantitative timing schedules: a free-operant schedule, in which rats were trained to distribute their responses differentially between two levers during the course of a 50-s trial (free-operant psychophysical procedure), and a discrete-trials schedule, in which rats were trained to discriminate the duration of light stimuli (interval bisection task).

METHODS

In experiment 1, rats were trained under the free-operant psychophysical procedure to respond on two levers (A and B) in 50-s trials in which reinforcement was provided intermittently for responding on A during the first half and on B during the second half of the trial. For one group, repetitive switching between levers was permitted; for another group, it was prevented. In experiment 2, rats were exposed to press lever A after a 2-s stimulus and lever B after an 8-s stimulus, and were then tested with stimuli of intermediate duration. For one group, a 'poke response' (depression of a central tray flap) was required after stimulus presentation to effect lever presentation; for the other group, this requirement did not operate. In both experiments, quantitative indices of timing were derived from the psychophysical functions (%B responding vs time).

RESULTS

In experiment 1, d-amphetamine increased the Weber fraction and displaced the psychophysical curve to the left in both versions of the schedule, as well as producing rate-dependent suppression of responding. In experiment 2, d-amphetamine increased the Weber fraction in both versions of the task without displacing the curve.

CONCLUSIONS

These results confirm the disruptive effect of d-amphetamine on timing. The results of experiment 1 are consistent with the proposal that the drug reduces the period of the hypothetical pacemaker. However, the results of experiment 2 do not support this suggestion. Taken together, the results support the notion that different neural mechanisms may be involved in timing tasks involving temporal distribution of responding and discrimination of the duration of exteroceptive stimuli.

Effect of central 5-hydroxytryptamine depletion on inter-temporal choice: a quantitative analysis

RATIONALE

It has been proposed that the ascending 5-hydroxytryptaminergic (5-HTergic) pathways are involved in "impulse control". Previous experiments have shown that rats whose 5-HTergic pathways have been destroyed are more liable than intact rats to select a smaller, immediate reinforcer rather than a larger, delayed reinforcer (impulsive choice). However, it remains unclear whether this effect of central 5-HT depletion reflects a change in the rate of time discounting (i.e. a change in the rate at which reinforcers become devalued as a function of delay) or a change in sensitivity to reinforcer size.

OBJECTIVE

We examined the effect of central 5-HT depletion on time discounting using a quantitative model of inter-temporal choice (multiplicative hyperbolic model), which enables effects on time discounting to be differentiated from effects on sensitivity to reinforcer size.

METHODS

Rats received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei or sham lesions. They were trained to press two levers for food-pellet reinforcers in a discrete-trials adjusting-delay schedule. In free-choice trials, selection of lever A resulted in a brief fixed delay (dA) followed by delivery of one pellet; selection of lever B resulted in a longer variable delay (dB) followed by delivery of two pellets; dB was adjusted in accordance with the subject's choices. The value of dA was varied (0.5-8.0 s) in successive phases of the experiment, and the indifference value of dB was determined in each case.

RESULTS

In both groups, the indifference value of dB was linearly related to the value of dA, in accordance with the multiplicative hyperbolic model. The lesioned group showed shorter indifference delays than the sham-lesioned group, this being reflected in a parallel displacement of the linear indifference function. In both experiments, the levels of 5-HT and 5-hydroxyindole-acetic acid were reduced in the brains of the lesioned rats, but the levels of noradrenaline and dopamine were not altered.

CONCLUSIONS

According to the multiplicative hyperbolic model, parallel displacement of the linear indifference function uniquely specifies a change in time discounting. Thus these results indicate that central 5-HT depletion results in an increase in the rate of time discounting for food reinforcers.

Theory and method in the quantitative analysis of "impulsive choice" behaviour: implications for psychopharmacology

Impulsive choice refers to the selection of small immediate gains in preference to larger delayed gains, or the selection of large delayed penalties in preference to smaller immediate penalties. Current theoretical interpretations of impulsive choice are reviewed, and a synthesis of these ideas, the "multiplicative hyperbolic model of choice", is presented. The model assumes that the value of a positive reinforcer increases as a hyperbolic function of its size, and decreases as a hyperbolic function of its delay and the odds against its occurrence. Each hyperbolic function contains a single discounting parameter which quantifies the organism's sensitivity to the variable in question. The hyperbolic discounting functions combine multiplicatively to determine the overall value of the reinforcer. Equivalent functions are postulated to govern the (negative) value of aversive events, the net value of an outcome reflecting the algebraic sum of the positive and negative values. The model gives rise to a quantitative methodology for studying impulsive choice, based on a family of linear indifference (null) equations, which describe performance under conditions of indifference, when the values of the reinforcers are assumed to be equal. This methodology may be used to identify individual differences in sensitivity to the magnitude, delay and probability of reinforcement. The methodology is also suitable for the quantitative evaluation of the effects of some pharmacological interventions on discounting parameters. Recent psychopharmacological studies of impulsive choice are reviewed, and the utility of indifference equations for extending this work, and developing a quantitative psychopharmacology of impulsive choice is discussed.

Effect of central 5-hydroxytryptamine depletion on changeover behaviour in concurrent schedules of reinforcement

RATIONALE

Previous experiments have shown that rats whose 5-hydroxytryptaminergic (5-HTergic) pathways have been destroyed exhibit higher rates of switching between response alternatives on various temporal differentiation schedules.

OBJECTIVE

This paper reports two experiments investigating the effect of central 5-HT depletion on switching between concurrent schedules of reinforcement which do not entail temporal differentiation of behaviour.

METHODS

Rats received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei or sham lesions. They were trained to press levers for sucrose reinforcement. In experiment 1, the rats were exposed to concurrent pairs of variable-time (VT) schedules specifying equal inter-reinforcement intervals; responses on a single "changeover lever" alternated between the two VT schedules. In experiment 2, the rats were exposed to concurrent pairs of variable-interval (VI) schedules specifying equal inter-reinforcement intervals; responses on one lever ("VI lever") earned reinforcers, while responses on the other lever ("changeover lever") alternated between the two VI schedules.

RESULTS

In experiment 1, both groups showed longer "dwell-times" (intervals between successive changeover responses) when a reinforcer was delivered in the "dwell" than when no reinforcer was delivered ("win-stay" effect). The lesioned rats showed higher rates of changeover responding and shorter dwell-times (with and without reinforcer delivery) than the sham-lesioned group. In experiment 2, the rate of responding on the VI lever did not differ significantly between the two groups; however, the lesioned rats showed higher rates of changeover responding, shorter dwell-times (with and without reinforcer delivery) and smaller numbers of inter-changeover responses on the VI lever than the sham-lesioned group. In both experiments, the levels of 5-HT and 5-hydroxyindoleacetic acid were reduced in the brains of the lesioned rats, but the levels of noradrenaline and dopamine were not altered.

CONCLUSIONS

These results provide further evidence for the involvement of the ascending 5-HTergic pathways in behavioural "switching", and indicate that this is not restricted to temporal differentiation schedules.

Effect of central 5-hydroxytryptamine depletion on performance in the free-operant psychophysical procedure: facilitation of switching, but no effect on temporal differentiation of responding

This experiment examined the effect of destroying the ascending 5-hydroxytryptaminergic (5-HTergic) pathways on timing and switching behaviour in the free-operant psychophysical procedure. Rats received injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei or sham lesions. They were trained to press levers for sucrose reinforcement; sessions consisted of fifty 50-s trials in which reinforcers were available on a variable-interval 30-s schedule. In the first 25 s, of each trial, reinforcement was only available for responses on lever A; in the last 25 s, it was available only for responses on lever B. In phase 1 (70 sessions) repetitive switching between the levers was prevented by withdrawal of lever A after the first response on lever B in each trial; in phase 2 (40 sessions) this constraint on switching was removed; in phase 3 (40 sessions) the constraint was reinstated. Data were collected from probe trials (four per session) in which no reinforcers were delivered, during the last ten sessions of each phase. In all phases, both groups showed declining response rates on lever A and increasing response rates on lever B as a function of time from the onset of the trial. Response rate on lever B, expressed as percentage of overall response rate, could be described by a two-parameter logistic function. Removal of the constraint on switching reduced the slope of the function without changing the indifference point (time corresponding to 50% responding on lever B). The parameters of the timing function did not differ between the groups in any of the phases. However, the lesioned group showed a greater enhancement of switching rate during phase 2 than the control group. The levels of 5-HT and 5-hydroxyindoleacetic acid were reduced in the brains of the lesioned rats, but the levels of noradrenaline and dopamine were not altered. The results provide further evidence for the involvement of the ascending 5-HTergic pathways in switching between response alternatives, but cast doubt on our previous suggestion that the effects of 5-HT depletion on temporal differentiation of behaviour are mediated by facilitated switching.

Dominant recognition of a cross-reactive B-cell epitope in Mycobacterium leprae 10 K antigen by immunoglobulin G1 antibodies across the disease spectrum in leprosy

Mycobacterium leprae-specific immunoglobulin G1 (IgG1) antibodies in patients with leprosy show a direct correlation with bacterial load (rho=0.748; P<0002) suggesting that IgG1 B-cell responses may be surrogate markers of disease progression. To investigate if this upregulation was a general feature of IgG1 responses to all M. leprae (ML) antigens, we analysed responses to several recombinant purified ML heat-shock proteins (HSP). Three recombinant HSPs (ML10 K, ML 18 K and ML 65 K) were tested for their ability to induce various IgG subclasses in patients with either the lepromatous (LL/BL, n=26) or tuberculoid form (BT/TT, n=39) of the disease as well as in healthy households (HC, n=14) and endemic controls (EC=19). Our major findings were: (1) selective augmentation of IgG1 antibody responses to ML10 K; (2) recognition of a restricted number of epitopes across the disease spectrum and healthy controls by IgG1 antibodies; (3) dominant recognition of cross-reactive epitopes which were common to both ML and MT 10 K. This response was not related to contamination with endotoxin. Epitope mapping using 15-mer overlapping peptides spanning the ML 10 000 MW revealed an immunodominant IgG1 binding peptide (aa41-55) in patients as well as healthy controls. This peptide is a shared epitope with M. tuberculosis 10 K suggesting that postswitched IgG1 B cells recognizing this epitope rather than naive B cells are being expanded.

Effect of central 5-hydroxytryptamine depletion on tolerance of delay of reinforcement: evidence from performance in a discrete-trials "time-left" procedure

This experiment examined the effect of destruction of the ascending 5-hydroxytryptaminergic (5HTergic) pathways on performance on a new discrete-trials version of the "time-left" procedure. Rats received either injections of 5,7-dihydroxytryptamine into the dorsal and median raphe nuclei or sham lesions. They were trained in a discrete trials schedule in which reinforcers were provided for responding on either of two levers, A and B. At a random time point, t s after the start of each trial, the two levers were inserted into the operant chamber: a response on A resulted in the delivery of one food pellet after dA s, whereas a response on B resulted in the delivery of two pellets after 84-t s. The value of dA was varied between 1 and 12 s in different phases of the experiment. Both groups showed an increasing tendency to respond on lever B as a function of time within the trial. Logistic functions were fitted to the data from each group, and a value of the "indifference point" (T50: the time within the trial at which proportional choice of B attained a value of 50%) was derived for each rat. For each value of dA, the values of T50 were significantly greater in the lesioned rats than in the control rats, reflecting a rightward shift of the logistic function in the lesioned group. The levels of 5HT and 5-hydroxyindoleacetic acid were reduced in the brains of the lesioned rats, but the levels of noradrenaline and dopamine were not significantly altered. The results provide further evidence for the involvement of the ascending 5HTergic pathways in the control of operant behaviour by delayed positive reinforcers.

Leprosy patients with lepromatous disease recognize cross-reactive T cell epitopes in the Mycobacterium leprae 10-kD antigen

T cell responses play a critical role in determining protective responses to leprosy. Patients with self-limiting tuberculoid leprosy show high T cell reactivity, while patients with disseminated lepromatous form of the disease show absent to low levels of T cell reactivity. Since the T cell reactivity of lepromatous patients to purified protein derivative (PPD), a highly cross-reactive antigen, is similar to that of tuberculoid patients, we queried if lepromatous patients could recognize cross-reactive epitopes in Mycobacterium leprae antigens as well. T cell responses were analysed to a recombinant antigen 10-kD (a heat shock cognate protein) which is available from both M. tuberculosis (MT) and M. leprae (ML) and displays 90% identity in its amino acid sequence. Lymphoproliferative responses were assessed to ML and MT 10 kD in newly diagnosed leprosy patients (lepromatous, n = 23; tuberculoid, n = 65). Lepromatous patients showed similar, but low, lymphoproliferative responses to ML and MT 10 kD, while tuberculoid patients showed much higher responses to ML 10 kD. This suggests that the tuberculoid patients may be recognizing both species-specific and cross-reactive epitopes in ML 10 kD, while lepromatous patients may be recognizing only cross-reactive epitopes. This was further supported by linear regression analysis. Lepromatous patients showed a high concordance in T cell responses between ML and MT 10 kD (r=0.658; P<0.0006) not observed in tuberculoid patients (r=0.203; P>0.1). Identification of cross-reactive T cell epitopes in M. leprae which could induce protective responses should prove valuable in designing second generation peptide-based vaccines.

Induction of Th1 cytokine responses by mycobacterial antigens in leprosy

Twelve mycobacterial antigens were compared for induction of gamma interferon (IFN-gamma) secretion by human blood mononuclear cells of patients with leprosy. Fractionated Mycobacterium leprae antigens containing cell wall proteins or cytosolic and membrane proteins induced good IFN-gamma responses in tuberculoid leprosy patients. Lipoarabinomannan from M. tuberculosis Erdman and M. leprae mycolylarabinogalactan peptidoglycan were the poorest IFN-gamma inducers.

Alterations in serum lipids in lepromatous leprosy patients with and without ENL reactions and their relationship to acute phase proteins

The concentrations of serum lipids were measured in patients with lepromatous (LL/BL) leprosy and erythema nodosum leprosum (ENL). The relationships between serum lipid levels and serum amyloid A (SAA) and C-reactive protein (CRP) were also examined in these patients. LL/BL patients had significantly higher serum triglyceride and lower HDL-cholesterol concentrations compared to the endemic controls. ENL patients had significantly lower total, HDL- and LDL-cholesterol levels compared to the endemic controls. The levels of all lipid metabolites also were significantly lower in ENL patients compared to LL/BL patients. The concentrations of SAA and CRP were markedly elevated in ENL patients but were not statistically different in LL/BL patients compared to control subjects. There was a significant negative correlation between SAA and HDL-cholesterol levels in both stable lepromatous and reactional (ENL) patients; there was no statistically significant correlation between CRP and HDL-cholesterol levels. SAA levels also had a significant negative correlation with total and LDL-cholesterol levels. Our results indicate that serum lipids are significantly altered in patients with lepromatous disease and ENL reaction. Our results also suggest that an increase in SAA levels may divert the metabolism of lipoproteins from hepatocytes toward macrophages, resulting in a decrease in serum lipoprotein levels.

Clinical and histological discrepancies in diagnosis of ENL reactions classified by assessment of acute phase proteins SAA and CRP

Sixteen out of 45 (36%) leprosy patients with clinical features of acute erythema nodosum leprosum (ENL) did not show the characteristic presence of neutrophils (polymorphs) in histology of the ENL lesion. The acute-phase reactants, serum amyloid A (SAA) and C-reactive protein (CRP) which are systemic markers of inflammation, and IgM and IgG antibody to Mycobacterium leprae were determined in these patients in order to understand the differences in histological diagnosis. Both SAA and CRP were elevated in ENL patients, irrespective of the presence of polymorph infiltrates, as compared to nonreactional lepromatous patients, patients with histologically confirmed reversal reactions and endemic controls, indicating that all clinically diagnosed ENL patients had ongoing inflammatory reactions. On the other hand, IgM and IgG antibodies were significantly lower (> 70%) in ENL patients as compared to nonreactional lepromatous patients. When the two ENL groups [ENL-PMN+ve (positive for neutrophils) and ENL-PMN-ve (negative for neutrophils)] were compared, there were no significant differences in the mean SAA, IgM or IgG antibody concentrations, but CRP was eightfold lower in ENL-PMN-ve as compared to the ENL-PMN+ve group. This may indicate that the timing or modulation of the reaction was different in the two ENL groups. Thus, measurement of the acute-phase response and the ratio of SAA/CRP in particular are helpful in the clinical diagnosis of ENL reactions in leprosy.

Immunoglobulin G1 (IgG1) and IgG3 antibodies are markers of progressive disease in leprosy

Mycobacterium leprae-specific and polyclonal immunoglobulin G (IgG) subclass and IgE antibodies in leprosy patients across the histopathological spectrum were determined by using a quantitative enzyme-linked immunosorbent assay. Antibody responses to M. leprae sonicates were detected only in IgG1, -2, and -3 subclasses. Even at 100-times-lower dilutions, very little IgG4 and IgE antibody activity against M. leprae was detected in any group of leprosy patients. Quantitatively, antibody responses were highest at the lepromatous pole and decreased towards the tuberculoid pole. The greatest quantitative difference in antibodies between the lepromatous and tuberculoid poles was observed with IgG1 (140-fold), this was followed by the difference with IgG3 antibodies (32-fold). Polyclonal antibodies, on the other hand, were elevated for all four IgG subclasses as well as IgE in both lepromatous and tuberculoid leprosy patients compared with healthy controls from a leprosy-endemic area. Selective elevation of M. leprae-specific antibody responses in IgG1 and IgG3 subclasses, therefore, could not be attributed to selective polyclonal activation in these particular subclasses. Furthermore, polyclonal activation for IgE was observed in both lepromatous and tuberculoid leprosy patients, with higher levels in the tuberculoid group, which does not support selective TH2 activation in lepromatous leprosy patients. IgG1 and IgG3 antibodies also showed the highest Spearman rank correlation with the bacterial index in these patients (rho = 0.748 and P < 0.001 for IgG1; rho = 0.721 and and P < 0.001 for IgG3). Thus, disease progression in leprosy showed a significant correlation with selective increases in IgG1 and IgG3 responses.

Recognition of Mycobacterium leprae recombinant 18,000 MW epitopes by IgG subclasses in leprosy

IgG subclasses are known to be differentially regulated by cytokines (elaborated by activated T cells), which act as growth factors and immunoglobulin switch factors on B cells. In leprosy, we have previously shown that IgG subclass antibodies to a purified recombinant antigen of Mycobacterium leprae (18,000 MW) are restricted to IgG1 and IgG3 across the disease spectrum. The only significant difference observed was that lepromatous patients with low to undetectable T-cell responses showed a strong correlation between IgG1 and IgG3 (P < 0.001) antibodies while tuberculoid patients who showed strong T-cell responses did not show such a correlation. To examine if these differences were related to T-cell-mediated class switching in tuberculoid leprosy patients, we have studied epitope recognition by IgG1 and IgG3 using a panel of synthetic peptides spanning the 18,000 MW molecule in an enzyme-linked immunosorbent assay (ELISA). In lepromatous patients there was little similarity in peptide recognition by IgG1 and IgG3, with IgG1 recognition being restricted to a single dominant carboxy-terminal peptide while the IgG3 antibodies recognized a diverse set of peptides in the N-terminal half of the 18,000 MW molecule. In tuberculoid patients both IgG1 and IgG3 antibody showed recognition of similar peptides in the N-terminal half of the 18,000 MW molecule. Our results therefore support the hypothesis that immunoglobulin class switching is occurring in tuberculoid but not in lepromatous patients.

IgG subclass antibody to Mycobacterium leprae 18,000 MW antigen is restricted to IgG1 and IgG3 in leprosy

IgG subclass responses to Mycobacterium leprae 18,000 MW recombinant antigen (18K) were determined in sera from untreated leprosy patients using an ELISA-based assay with specific monoclonal antibodies. Antibodies to M. leprae 18K were restricted to IgG1 and IgG3 antibodies with higher seropositivity in lepromatous patients (25.5% for IgG1 and 12.8% for IgG3) compared to patients with tuberculoid disease (11.5% for IgG1 and 5% for IgG3). No significant antibody response was detectable in IgG2 and IgG4 in patients with either lepromatous or tuberculoid leprosy. The selective production of antibodies in IgG1 and IgG3 subclasses could not be related to polyclonal activation in these subclasses as all IgG subclasses showed similar elevated levels at the polyclonal level. The major difference noted between lepromatous and tuberculoid leprosy patients with the IgG subclass antibody response was a strong linear correlation between IgG1 and IgG3 responses to M. leprae 18K in lepromatous patients (r = 0.703, P < 0.001) but not in tuberculoid leprosy patients (r = 0.007, P > 0.10) which may be related to immunoglobulin class switching of IgG3 to IgG1 rather than selective shifts in T-helper subsets. Our results therefore, do not support the hypothesis that activation of Th2 cells occurs in lepromatous leprosy; this issue needs further examination.

Antigen-coated latex particles as a model system for probing monocyte responses in leprosy

To study responses to Mycobacterium leprae antigens, we developed an in vitro model system in which latex particles coated with M. leprae sonic extract (MLSON) antigen were presented to monocytes. Uptake and oxidative response as measured by superoxide production to these antigens were investigated. Phagocytosis of MLSON-coated particles was greater than that of control particles in monocytes from both leprosy patients and controls from leprosy-endemic areas; uptake of MLSON-coated particles was higher in monocytes from lepromatous leprosy patients than in cells from tuberculoid leprosy patients and controls. In both patients and controls, uptake of latex particles coated with leprosy antigens triggered very little reduction of nitroblue tetrazolium although the cells were capable of mounting a respiratory burst. Antigen-coated latex particles can therefore be used as a tool to investigate monocyte responses to M. leprae and individual recombinant antigens.

Use of polymerase chain reaction to assess efficacy of leprosy chemotherapy

The assessment of chemotherapy efficacy in leprosy is difficult, since the only reliable method for determining whether the causative organism, Mycobacterium leprae, is viable depends on its growth in mouse foot pads. In an attempt to replace this expensive, time-consuming test, methods based on the polymerase chain reaction (PCR) have been developed. These methods depend on detection of DNA, which is more susceptible to degradation on cell death than are other cell components, so should be a more accurate indicator of viability. We have used a specific PCR assay to detect M leprae DNA in skin biopsy samples from leprosy patients. By use of limiting dilution PCR (LD-PCR), the concentration of M leprae DNA in the original sample could be measured. The DNA concentration was more closely correlated with the morphological index (derived from a staining technique that distinguishes morphologically intact and damaged bacteria) than with the number of bacteria visible (bacterial index, BI, which counts both alive and dead bacteria). In a longitudinal study of multibacillary patients on multi-drug therapy, skin biopsy samples were collected before treatment and 3, 6, 12, and 24 months after the start of therapy. While the BI showed little or no change during treatment, the number of genomes detected by PCR fell sharply, in parallel with the MI. We propose that PCR can be used as a rapid measure of M leprae viability and that this approach can be used for monitoring individual leprosy patients and for assessment of existing and new regimens. The method may be applicable to other infectious diseases in which culture of the causative organism is slow or impossible.

Recognition of Mycobacterium leprae recombinant 18-kDa proteins in leprosy

Three different, purified, Escherichia coli-derived, recombinant preparations of the Mycobacterium leprae 18K protein were compared for their immunological recognition in leprosy. The preparations tested were 18K fusion proteins containing 70% (amino acids 38-148) of the full 18K protein fused to either a short leader sequence containing six asparagine residues or to beta-galactosidase, and the full length 18K protein. All three recombinant antigens were recognized by IgG antibodies which were restricted mostly to lepromatous leprosy patients. The 18K antigen with the asparagine leader sequence showed better reactivity with IgG antibodies compared with the other two 18K preparations. In lymphocyte proliferation assays, the truncated 18K and the full-length 18K showed equivalent responses in the same donors with strongest recognition in donors who were also strongly responsive to the M. leprae soluble sonicate. These results indicate that the major human B- and T-cell epitopes are located within the segment 38-148, although some individuals may recognize additional epitopes at the NH2-terminal end.

Detection of high titres of Toxoplasma gondii antibodies in sera of patients with leprosy in Pakistan

Untreated and treated leprosy patients and their household contacts were screened for antibody to Toxoplasma gondii using antigen-coated latex particles. A significantly high level of seroprevalence (29.6%) was observed in the untreated leprosy patients compared to endemic controls (P < 0.01) with a mean reciprocal antibody titre of 20,007 +/- 3580 (n = 98) in seropositive patients. In treated patients seroprevalence dropped to 13.5%. Seroprevalence in a group of household contacts of leprosy patients was similar to that of control subjects from an endemic area but not exposed to leprosy (7.8% and 6.1% respectively), indicating that the increased seroprevalence in leprosy patients was not merely due to increased exposure related to socioeconomic factors. Antigenic cross-reactivity between T. gondii and Mycobacterium leprae antigens was ruled out by cross inhibition experiments carried out with soluble antigens from each of the organisms. We believe these antibodies may be induced by an increase in T. gondii load in leprosy due to a transient reactivation of latent T. gondii infections, as the antibodies in these leprosy patients were not associated with any sign of eye or lymphatic pathology related to toxoplasmosis.

Specificity of lymphocytotoxic autoantibodies (LCAbs) found in the serum of leprosy patients: class I MHC antigens

Lymphocytotoxic autoantibodies (LCAbs) of the IgM class have been identified in patients with borderline tuberculoid (BT) and borderline lepromatous (BL) leprosy with Type I reactions (I) as well as lepromatous leprosy (LL) patients with erythema nodosum leprosum reactions (ENL). The observation that lymphocytotoxic activity (LCA) was reduced in the presence of platelets led us to determine whether LCAbs had specificities for Class I Major Histocompatibility Complex (MHC) determinants. Absorption of LCA positive sera with platelets, classically used to deplete Class I specific lymphocytotoxic antibodies, reduced LCA towards autologous as well as allogeneic target cells. This was true for LCA positive sera from all patient classifications (group BT in the autologous system, p less than 0.01; in all other patient groups, p less than 0.001). Introducing B-2m to cytotoxicity assays only marginally reduced LCA when added at high concentrations (5 mg/ml). An anti-Class I MHC antiserum which blocked the lytic activity. The data indicate that LCAbs while absorbed by platelets, are not specific for the Class I MHC antigens. The autoantigen recognized by these autoantibodies therefore remains to be identified.

Serum lymphocytotoxic activity in leprosy

Sera from 167 patients across the spectrum of leprosy and 46 endemic controls were screened for lymphocytotoxic activity (LCA). The Terasaki microdroplet lymphocytotoxicity assay was performed at 37 degrees C and 15 degrees C to test sera for LCA against a panel of lymphocytes from 50 donors which represented most known HLA-ABC antigens. Raised complement-dependent LCA at 15 degrees C was seen in leprosy patients with histories of erythema nodosum leprosum (ENL) or reversal/Type I (I) reactions. Eighty-six per cent of lepromatous (LL) patients with a history of ENL (n = 21, P less than 0.001), 83% of borderline lepromatous (BL) and 88% of borderline tuberculoid patients (BT) with a history of Type I reactions (n = 12, P less than 0.01 and n = 24, P less than 0.001 respectively) had LCA compared to 39% of endemic controls (n = 46). LCA was attributed to IgM on the basis of reduced activity when serum was treated with both dithiothreitol or absorbed with antiserum for IgM. Removal of immune complexes and rheumatoid factor did not influence LCA. LCA-positive sera reacted similarly with allogeneic lymphocytes from either healthy donors or leprosy patients. Moreover LCA-positive sera reacted with autologous lymphocytes. Specificities for HLA-ABC antigens were not identified. The potential role of these autoantibodies, manifested in leprosy patients with hypersensitivity reactions remains speculative.