Anti-acetylcholine receptor IgG in neonatal myasthenia gravis

Detection of Anti-Phospholipid and Anti-DNA Antibodies and their Idiotypes in Newborns of Mothers with Anti-Phospholipid Syndrome and Sle

The titers, isotypes and idiotypes of antiphospholipid and anti-dsDNA antibodies were determined in seven pairs of mothers with antiphospholipid syndrome (APLS) and their offspring, in 11 pairs of SLE mothers and their matched infants and in seven respective pairs of healthy subjects. In addition, maternal as well as fetal sera were evaluated for the presence of anti-SSA (Ro), anti-SSB (La) and anti-70 kd RNP autoantibodies.

In the sera from APLS patients, as well as in the sera from their offspring, the mean antibody titer of IgG aCL was found to be significantly higher then the corresponding value in the control group (P < 0.01). Highly significant increased titers of IgG anti-DNA antibodies were found in the sera of SLE mothers and their matched offspring (P < 0.0008).

The prevalance of anti-SSA, anti-SSA, and anti-7OKd RNP antibodies was lower then that of antiphospholipid and anti-dsDNA antibodies. Only one of the respective offspring had increased levels of these antibodies.

The quantity of maternal antibodies transferd to the fetus was depended on their concentration in the maternal circulation, as well as on their type and specificity. Follow-up of newborn sera showed a progressive decrease in the antiphospholipid antibody titers during 3 months. After 6 months it was undetected.

Our results point to a transplacental transfer of aCL and anti-DNA antibodies, a phenomenon which is not necessarily associated with respective clinical manifestations, in contrast to the classical humoral mediated autoimmune diseases (e.g. myasthenia gravis).

Experimental neonatal autoimmune myasthenia gravis: an immunohistochemical, ultrastructural and electrophysiological study of the motor end-plate

Neonatal rats born of and nursed by mothers immunized with Narke japonica acetylcholine receptor protein had elevated serum anti-acetylcholine receptor antibodies that reached the mother's level on day 10 after delivery and decreased rapidly after weaning. IgG was present at the motor end-plates up to day 170, and the motor end-plate fine structure remained abnormal up to day 80. Miniature end-plate potential amplitudes in the diaphragm were at the control levels within 10 days of birth, but were lower than those of the controls up to day 80 after birth. We could not obtain the direct evidence that transient synthesis of antibodies occurs in experimental autoimmune myasthenia gravis pups. This model can serve as an experimental model of transient neonatal myasthenia gravis in humans, exception for the route of antibody transfer and the time of the onset of illness.

Detection of anti-phospholipid and anti-DNA antibodies and their idiotypes in newborns of mothers with anti-phospholipid syndrome and SLE

The titers, isotypes and idiotypes of antiphospholipid and anti-dsDNA antibodies were determined in seven pairs of mothers with antiphospholipid syndrome (APLS) and their offspring, in 11 pairs of SLE mothers and their matched infants and in seven respective pairs of healthy subjects. In addition, maternal as well as fetal sera were evaluated for the presence of anti-SSA (Ro), anti-SSB (La) and anti-70 kd RNP autoantibodies. In the sera from APLS patients, as well as in the sera from their offspring, the mean antibody titer of IgG aCL was found to be significantly higher then the corresponding value in the control group (P < 0.01). Highly significant increased titers of IgG anti-DNA antibodies were found in the sera of SLE mothers and their matched offspring (P < 0.0008). The prevalence of anti-SSA, anti-SSA, and anti-70Kd RNP antibodies was lower then that of antiphospholipid and anti-dsDNA antibodies. Only one of the respective offspring had increased levels of these antibodies. The quantity of maternal antibodies transferred to the fetus was depended on their concentration in the maternal circulation, as well as on their type and specificity. Follow-up of newborn sera showed a progressive decrease in the antiphospholipid antibody titers during 3 months. After 6 months it was undetected. Our results point to a transplacental transfer of aCL and anti-DNA antibodies, a phenomenon which is not necessarily associated with respective clinical manifestations, in contrast to the classical humoral mediated autoimmune diseases (e.g. myasthenia gravis).

Transient neonatal myasthenia gravis

Transient neonatal myasthenia gravis is a postsynaptic neuromuscular transmission defect occurring in 21% of infants born to women with active (and, less commonly, in remission) acquired myasthenia gravis. Although passive-transfer acetylcholine receptor (AChR) antibodies are found in the majority of these newborns, their pathogenic role is questionable because only some infants are symptomatic. Pathogenesis in infants without AChR antibodies is unknown. There is still no biologic marker for prenatal identification of this subpopulation of newborns, although HLA typing may be a promising tool. Sucking, swallowing, and respiratory difficulties are the most common presenting signs in the first day of life. Final diagnosis is done when administration of acetylcholinesterase agents transiently corrects the neuromuscular transmission defect. Serum AChR antibody titers follow the same pattern as their mothers. Supportive management and anticholinesterase agents prior to feedings are necessary in about 80% of patients. In the majority of infants the condition resolves spontaneously.

Anti-acetylcholine receptor antibodies in neonatal myasthenia gravis: heterogeneity and pathogenic significance

Precipitating, blocking and modulating anti-AChR antibodies and their capacity to recognize embryo or adult muscle were investigated in parallel in maternal and neonatal sera of fifty-two newborns and their myasthenic mothers. Twenty-four babies presented neonatal myasthenia gravis (NMG) with a common expression in twenty cases and foetal involvement in four cases. Occurrence of NMG was clearly related to levels of maternal precipitating, decamethonium blocking (DC blocking) and modulating antibodies (respectively P less than 0.001, P less than 0.02, P less than 0.01, Mann-Whitney test), these three parameters being interrelated. The only significant difference between mothers with severely affected babies and others with mild NMG newborns concerned DC blocking antibodies. Transfer fraction of DC blocking antibodies was significantly higher in NMG than in asymptomatic babies. Our data suggest that (1) the amount of anti-AChR antibodies, whatever the tested category, is involved in the pathogeny of NMG in a more direct manner than in adult MG where the correlation with their levels is poor, and (2) among antibodies, those with blocking effects could be preponderant for triggering NMG and be involved in the severity of the disease in the child.

Alpha-bungarotoxin blocking antibodies in neonatal myasthenia gravis: frequency and selectivity

We have studied antibodies to the acetylcholine receptor (AChR) that inhibit alpha-bungarotoxin binding in 22 mothers with myasthenia gravis (MG) and in their 23 newborns. Of the 13 showing neonatal MG, seven of the mothers had detectable direct blocking antibodies, all 13 had decamethonium-dependent (DC) blocking, and nine had high titres of precipitating antibodies (greater than 40 nM). In those with symptom-free newborns, the corresponding figures were 2/10, 8/10 and 2/10; the mean titres of DC blocking and of precipitating antibodies were 5- and 3-fold lower than in the mothers of affected babies. Thus, blocking antibodies, in addition to high total antibody levels, may help to predict the occurrence of neonatal MG. However, the antibodies appear not to cross the placenta to the same extent in each case. 86, 69 and 84% of the maternal antibodies with precipitating, direct and DC blocking activities, respectively, were found in the myasthenic neonates versus 65, 28 and 44% in the unaffected. These data suggest (1) involvement of blocking antibodies in the pathogenesis of MG, and (2) variable placental transfer of anti-AChR antibodies, which makes neonatal affliction more difficult to predict.

Plasma exchange in myasthenia gravis: effect on anti-AChR antibodies and other autoantibodies

Plasma exchange (PE) was performed in 6 patients with myasthenia gravis (MG). Acetylcholine receptor (AChR) antibodies and other MG-correlated antibodies were quantified each day before, during and after PE. The antibody concentrations decreased during PE with a consisting increase between two exchanges. Repeated PE induced a transient decline in the AChR antibody concentration. The clinical improvement was maximal during the week after PE and correlated in time with increasing concentrations of AChR antibodies.

Plasma exchange in myasthenia gravis: clinical effect

Seventeen patients suffering from myasthenia gravis were treated with plasma exchange. Serious complications were not encountered. The effect usually appeared on the second or the third day of treatment. In 12 patients with a total of 31 plasma exchange courses, the treatment resulted in a shift in Osserman group. Six of these had long-standing remissions. Three patients responded moderately and two patients did not respond to plasma exchange.

Autoimmunity and pregnancy

The general effect of pregnancy on autoimmunity remains controversial. In the majority of cases, pregnancy may have no effect on the disease, while on other occasions, pregnancy induces exacerbations that may be especially pronounced in the immediate post-partum period. The reasons for this preponderance are still unclear. Another important aspect of autoimmune diseases during pregnancy entails the passive transfer of the disease into the fetal compartment. It seems that until the pathogenesis and a better specific therapy for autoimmune diseases are clearly defined, careful clinical and immunologic observation of each mother-infant pair will be invaluable.

Transplacental transmission of experimental autoimmune myasthenia gravis. A morphological study

Using neonates born from experimental autoimmune myasthenic rabbits, the authors demonstrated antibodies to acetylcholine receptor (AChR) in the newborn sera. By radioimmunoassay, antibody titers of 1-day-old neonates were roughly one seventh to one ninth of the mothers. At 8 weeks postpartum, the antibody was no longer detectable. Ultrastructural observations of the intercostal muscles of the neonates revealed two types of changes. The first type was degenerative alterations in the postsynaptic membrane. The second type of change, which was morphometrically analyzed, was immaturity of postsynaptic membrane structure with underdeveloped secondary synaptic clefts. After 28 days postpartum, these changes were not visible, thereby indicating that the process is reversible as the antibody titer decreases. These results suggested the possibility that the antibody to AChR, transferred transplacentally, arrested the development of postsynaptic structure, although reversible, by blocking of the receptor sites in the end-plate.

Myasthenia gravis, thymectomy and serum thymic hormone activity

Serum thymic hormone activity was measured in 36 patients with myasthenia gravis and in 10 control subjects from each age decade. In all 25 patients under 50 years of age results were within, or close to, the normal range. Activity at levels considered normal for juveniles was detected in 10 of the 11 older patients whereas levels normally decline in older subjects. One week after thymectomy, 13 of 17 patients (76 per cent) had no demonstrable serum thymic hormone activity. However, 10 months or longer after thymectomy only five patients (30 per cent) lacked thymic hormone activity in the serum. There was a significant correlation between clinial improvement and sustained lowering of serum thymic hormone activity after thymectomy.

Myasthenia gravis: review of diagnosis and management

Although the cause of myasthenia gravis is still unknown, its pathogenesis appears clear: immunologic attack on synaptic receptors in muscle causes receptor deficiency, decreased miniature endplate potentials, and decrements in the compound action potentials evoked from muscles on repetitive stimulation of peripheral nerves. In addition to the involvement of skeletal muscle, some MG patients may manifest subtle alterations of the function of heart, lung, smooth muscle, and CNS, indicating that this is truly a systemic disorder. Modern therapy involves adjusting treatment to the needs of individual patients. Anticholinesterases, calcium, ephedrine, potassium, and germine partially correct the defect in neuromuscular transmission; prednisone, ACTH, cytotoxic drugs, antilymphocyte serums, gamma globulin, thoracic duct drainage, plasmapheresis, and thymectomy partially modify the abnormalities of the immune system.

Neonatal experimental autoimmune myasthenia gravis

Neonatal rats born of and nursed by mothers immunized with Torpedo acetylcholine receptor protein developed a defect of neuromuscular transmission as indicated by reduced miniature endplate potential amplitudes. It is likely that antibodies to the Torpedo receptor protein were passively transferred to the neonates in the milk. With the exception of the route of transfer, this neonatal form of experimental autoimmune myasthenia gravis appears to be similar to its human counterpart, and thus can serve as an experimental model.