Metabolism of Autologous and Homologous IgG in Rheumatoid Arthritis

Abstract

A B S T R A C T The metabolism of radioiodinated IgG was studied in 20 patients with rheumatoid arthritis and 11 normal controls using autologous IgG and homologous IgG pooled from normal donors. Fractional catabolic rates in the controls were 4.44% of the autologous-and 4.29% of the homologouslabeled protein per day. The corresponding rates in the rheumatoid patients were 9.67% of the autologousand 8.64% of the homologous-labeled protein per day. Extravascular catabolism occurred only in the rheumatoid group and accounted essentially for the entire increased catabolism ofIgG observed in these patients. 10 patients were especially hypercatabolic, with fractional catabolic rates for autologous IgG greater than 10%. Moreover, they catabolized their autologous IgG significantly faster than the homologous IgG (12.6 vs. 9.9%). The increment of catabolism of autologous over homologous IgG also occurred in the extravascular compartment. These highly hypercatabolic patients had a significantly increased number of manifestations of extra-articular disease.The hypercatabolism of IgG could not be correlated with age, weight, sex, duration of disease, joint erosions, corticosteroid therapy, erythrocyte sedimentation rate, rheumatoid factor titer, serum IgG concentration, or circulating immune complexes as measured by the Raji cell radioimmunoassay.Conceivable sites of extravascular catabolism and possible causes of faster catabolism of autologous (rheumatoid) than of homologous (normal) IgG are discussed.

Importance of the IgG isotype, not the state of glycosylation, in determining human rheumatoid factor binding

“…This, however, does not appear to be the case. The catabolism of radiolabeled autologous IgG is faster in patients with RA than in normal controls (34). Thus, from the information available, the lack of the galactose on the Fc fragment does not appear to prolong the half-life of the IgG molecule in patients with RA.…”

Molecular properties of the Ro/SSA antigen and enzyme-linked immunosorbent assay for quantitation of antibody.

“…who showed only anti-Ro/SSA precipitins in immunodiffusion to cyanogen bromide-activated Sepharose 4B (Pharmacia Fine Chemicals, Piscataway, NJ) by the method suggested by the manufacturer. IgG was prepared by DEAE-cellulose chromatography (13) (20,21). Samples and standards were applied to a 10% polyacrylamide gel containing 7 M urea.…”

Murine thymocytes possess specific cell surface‐associated exoaminopeptidase activities: Preferential expression by immature CD4−CD8− subpopulation

“…It is a zinc metalloprotease that removes NH2-terminal neutral amino acids from peptides and which also shows a broad specificity in the cleavage of basic and acidic residues.Very recently, this enzyme has been identified on the cell surface antigen CD13 expressed by human myeloid leukemia cell lines [26]. This molecule also appears to be expressed by leukemic blasts from patients with acute B lymphoid leukemia [27] as well as on cells of granulocyte-Ma lineage at all the stages of differentiation [28,29]. Amoscato and colleagues have reported the presence of a surface Leuaminopeptidase-like activity on resting human lymphocytes, which is enhanced upon mitogenic stimulation [30].…”