Evidence for activation of the alternate complement pathway in patients with juvenile rheumatoid arthritis.
OBJECTIVE
Complement activation has been shown to occur in patients with juvenile rheumatoid arthritis (JRA). Since the two pathways of complement are activated by different stimuli (the alternate pathway by microbial products and IgA, and the classical pathway by immune complexes), we decided to study the relative contribution of the two pathways of complement activation in patients with JRA.


METHODS
In 56 patients with JRA, plasma levels of C3 and C4 were measured by turbidimetric assays, and those of C4d, factor Bb and sC5-9 complex by solid-phase enzyme immunoassays. Levels beyond the mean +/- 2 S.D. of normal were considered abnormal.


RESULTS
Plasma C3 and C4 levels were decreased in one patient each. The C4d values were increased in 17 patients, whereas levels of factor Bb were elevated in 42 patients and levels of sC5-9 complex were elevated in 51 patients. The values of factor Bb and sC5-9 had a linear correlation (r = 0.75), but there was no significant correlation between C4d and sC5-9 levels (r = 0.36).


CONCLUSIONS
Complement activation in JRA is initiated predominantly by the alternate pathway and culminates in the formation of terminal membrane attack complex.
Aggarwal
A
A
Department of Clinical Immunology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow 226 014, India.
Bhardwaj
A
A
Alam
S
S
Misra
R
R
D000293:Adolescent; D000936:Antigen-Antibody Complex / Q000276:immunology; D001171:Arthritis, Juvenile / Q000097:blood / Q000276:immunology*; D000077214:Becaplermin; D001799:Blood Sedimentation; D002097:C-Reactive Protein / Q000032:analysis; D002648:Child; D002675:Child, Preschool; D003167:Complement Activation; D003176:Complement C3 / Q000276:immunology; D003181:Complement C4 / Q000276:immunology; D015935:Complement C4b; D003182:Complement C5 / Q000276:immunology; D003170:Complement Pathway, Alternative / Q000276:immunology*; D006801:Humans; D007124:Immunoenzyme Techniques; D010446:Peptide Fragments / Q000276:immunology; D010982:Platelet-Derived Growth Factor / Q000276:immunology; D020574:Proto-Oncogene Proteins c-sis
D000936:Antigen-Antibody Complex; D003176:Complement C3; D003181:Complement C4; D003182:Complement C5; D010446:Peptide Fragments; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D000077214:Becaplermin; D015935:Complement C4b; C032261:complement C4d; D002097:C-Reactive Protein