Faculty Bibliography

The neonatal lupus syndromes, which comprise transient hematologic and cutaneous disorders as well as the permanent manifestation of heart block, are considered to result from injury by passively acquired maternal autoantibodies. The active placental transport of maternal IgG antibodies becomes operative late in the second trimester coincident with the time at which bradycardia and myocarditis become evident. Surprisingly there are no clinically detectable abnormalities in the maternal hearts. The recognition that antibodies to the SSA/Ro-SSB/La ribonucleoprotein complex were found in 85% of sera from mothers of offspring with neonatal lupus was an important advance and directed attention to these antigens as potential candidates despite their intracellular location. In the present review we describe an experimental approach to the treatment of a fetus diagnosed by in utero echocardiogram to have congenital complete heart block and to the prevention of this condition in an at-risk pregnancy. In an attempt to more specifically define the relevant antigen-antibody systems involved in the pathogenesis of neonatal lupus we have utilized the technique of immunoblot to evaluate sera from mothers of offspring with permanent manifestations of neonatal lupus including heart block and hepatic fibrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

The molecular basis of autoantibody reactivity with components of the SSA/Ro-SSB/La particle exhibited by sera of mothers of infants with severe and permanent manifestations of neonatal lupus (NLE) was investigated using immunoblotting and immunoprecipitation. The characteristics of NLE that were studied included congenital complete heart block (CCHB), second degree heart block, and hepatic fibrosis. Antibodies specific for one or more components of the SSA/Ro-SSB/La particle were found in sera from all 20 mothers of permanently affected infants. However, no antibody specific for a single peptide of this particle was common to all sera. Using tissue extracts from a human cell substrate, 80% of these sera had antibodies to one or more components of the SSA/Ro particle demonstrable by immunoblotting. The predominant antibody response in the NLE group was to the newly recognized 52-kD SSA/Ro peptide component. In contrast, antibodies to the 60-kD SSA/Ro component although present, were the least represented and not significantly increased in frequency among mothers of these infants, compared with a group of 31 mothers with autoimmune diseases such as systemic lupus erythromatosus (SLE) but who had healthy offspring. Antibodies directed to the 48-kD SSB/La antigen were demonstrated in 90% of the NLE mothers often accompanying antibodies against the 52-kD SSA/Ro component. The combination of antibodies to 48- and 52-kD structures was significantly increased in the NLE group, with an odds ratio of 35. The type of cell or tissue substrate was shown to influence detectability of antibodies. The 52-kD SSA/Ro peptide and the 48-kD SSB/La peptide were abundant in cardiac tissues from fetuses aged 18-24 wk, further supporting the possible relevance of these peptides to heart block

The neonatal lupus syndrome is the most common cause of isolated congenital heart block. There is, at present, little information about the putative role of anti-SS-A/Ro SS-B/La antibodies in the pathogenesis of congenital heart block in the neonatal lupus syndrome. Using an in vitro experimental model, the present study was designed to test the hypothesis that IgG antibodies in the sera of anti-SS-A/Ro SS-B/La-positive mothers of infants with isolated congenital heart block bind to and affect the transmembrane action potential of rabbit cardiac tissue. The results demonstrate a preferential inhibition of membrane repolarization (ADP-50 and ADP-90) and staining of cardiac cells within the neonatal, in contrast to the adult, rabbit heart by sera and IgG-enriched fractions from anti-SS-A/Ro SS-B/La-positive individuals. The results of the electrophysiologic studies demonstrate a pathophysiologic role for the IgG fraction of anti-SS-A/Ro SS-B/La-positive maternal sera in inhibiting neonatal rabbit cardiac repolarization. It is possible that antibodies to similar determinants expressed on the cell membrane of cardiac-conducting cells also may play a pathophysiologic role in the development of idiopathic congenital heart block in humans

The physicochemical properties of apparently acid-labile IFN-alpha from patients with SLE have been studied. The antigenicity, apparent molecular size, and isoelectric point of SLE IFN-alpha are indistinguishable from those of conventional, previously characterized, acid-stable subspecies of IFN-alpha. However, after partial purification by anion-exchange chromatography, SLE IFN-alpha no longer exhibits acid lability, suggesting that other plasma factor(s) are responsible for the acid lability of SLE IFN-alpha. Addition of SLE plasma, but not normal plasma, to conventional acid-stable IFN-alpha renders the exogenous IFN-alpha acid labile. Preliminary results demonstrate that an acid-dependent IFN-inactivating activity can be partially purified from SLE plasma by anion-exchange chromatography

The iC3b receptor (CR3) is required for neutrophil adhesive functions, including homotypic aggregation. Because stimuli that enhance neutrophil adhesion also induce up-regulation of surface CR3, it is widely held that these two responses are causally related. We have dissociated CR3 display (immunofluorescence) from CR3 function (aggregation). Neutrophils isolated at 4 degrees C and rewarmed to 37 degrees C up-regulated surface CR3 twofold, but did not aggregate. The kinetics of FMLP-induced CR3 up-regulation were discordant with those of aggregation. In the absence of extracellular divalent cations, CR3 expression increased twofold after exposure to FMLP, but neutrophils did not aggregate. FMLP elicited 3.5-fold more aggregation than the ionophore A23187, yet less than one-half as much CR3 up-regulation. 3 mM sodium salicylate inhibited aggregation 55 +/- 4%, but had no effect on CR3 up-regulation. Conversely, 1 mM tetracaine completely inhibited CR3 up-regulation, while significantly enhancing aggregation. Neutroplasts expressed CR3, but did not up-regulate the receptor; in contrast, FMLP induced CR3-dependent aggregation of neutroplasts. We conclude that, although constitutive surface CR3 is required for neutrophil aggregation, the up-regulation of CR3 is neither necessary nor sufficient to promote cell-cell adhesion

A retrospective literature review revealed that in 41% of cases of complete congenital heart block (CCHB) there was at least one other affected sibling, emphasizing the considerable risk of carrying a second affected fetus with CCHB. Therefore an aggressive approach was taken to prevent CCHB in a fetus with a high risk for the condition as defined by (1) presence of DR3 and high titers of antibodies to SSA(Ro) and SSB(La) in the mother (2) previous history of CCHB in a sibling. In a feasibility study, thrice weekly plasmapheresis was initiated in the 19th week of gestation to remove antibodies from the maternal circulation in advance of major placental transport to the developing fetus. Prednisone was also administered to decrease antibody synthesis. The concentration of total maternal IgG and antibodies to SSA(Ro) and SSB(La) were decreased by greater than 60% during the course of therapy. Planned delivery of a healthy baby was done at 36 weeks

Whether homotypic neutrophil aggregation depends on the quantitative increase of gp165/95 molecules (Mac 1, CR3) recruited to the cell surface during activation was studied using mAb of the CD11b group that recognize distinct epitopes encoded by the alpha-subunit of this glycoprotein. After the addition of antibody MN41, neutrophils did not aggregate in response to a chemoattractant, FMLP. Blockade of preexisting surface gp165/95 by mAb MN41, followed by removal of the excess antibody from the mixture, was used to show that the molecules of gp165/95 newly expressed in response to stimulation by a chemoattractant were incapable of effectively mediating the induced cell-cell interactions of aggregation. Flow cytometry studies confirmed that binding of unlabeled antibody MN41 did not block further increases in surface expression of gp165/95 after stimulation with FMLP. These data suggest that molecules of gp165/95 exhibit two functionally distinct forms, one, present on the surface of freshly isolated neutrophils, that becomes competent to mediate the aggregation response upon activation by a stimulus and a second form that can be translocated to the cell surface by the stimulus but is greatly diminished if not lacking in the ability to participate in that aggregation event