Significance oflowmolecular weight Clqin systemic lupus erythematosus

Thesignificance ofhigsenum concentrations oflowmolecular weight Clq(LMW-Clq) in patients withsystemic lupuserythematosus (SLE) wasstudied. Concentrations ofLMWClqwereincreased inSLE,butnotin rheumatoid arthritis oracute poststreptococcalglomerulonephritis. Concentrations of LMW-ClqinSLEserumsamples correlated withtitres ofanti-dsDNA andwereinversely related toconcentrations ofnormal Clqand C3.Serial studies insixpatients, whohad rising anti-dsDNA titres andwhodeveloped a majorexacerbation requiring admission to hospital, showed that LMW-Clqincreased in paralel with anti-dsDNA, reachingpeakvalues ofmorethan2000%/o ofnormal just before orat thetimeofclinical relapse anddecreasing during convalescence. Mostmarked increases inLMW-Clqwerenoted inthethree patients inwhomClqconcentrations remained normal, whereas increases werelessinthethree patients whohadstrongly depressed concentrations ofnormalClq.A studyofClq biosynthesis bymacrophages cultured from patients withSLEandhighserumconcentrations ofLMW-Clqdidnotshowimpaired secretion ofnormal Clqinfavour ofLMWClq,butindicated that serumconcentrations ofLMW-Clqmayreflect thesynthetic rate of Clqinvivo. Theresults showthat increased serumconcentrations ofLMW-Clqmaybe helpful indiagnosing SLEandsuggest that serial determination ofLMW-Clqinserum may havepredictive valueinmonitoring patients withSLE.