The effect of extracorporeal antibody removal on antibody synthesis and catabolism in immunized rabbits.

Plasma exchange therapy is currently used to remove antibody from the circulation in a number of autoimmune diseases. It has been suggested that the decrease in antibody level may affect synthesis rate by the removal of inhibitory feedback. This would then cause a rapid rise in antibody levels to or beyond those prior to depletion. Based on this supposition immunosuppression is nearly always used concomitantly with plasma exchange to prevent the expected increase in synthesis rates. An assessment of the effect of specific antibody removal by immunoadsorption on synthesis and catabolic rates was undertaken to clarify the nature of the response. Rabbits were immunized to bovine serum albumin (BSA) injected with 125I-anti-BSA IgG and later underwent extracorporeal immunoadsorption with BSA-Sepharose. At least 60% of circulating anti-BSA-IgG was removed. Mathematical analysis of 125I-anti-BSA IgG and anti-BSA-IgG levels demonstrated a reduction in catabolic clearance following immunoadsorption. Conversely synthesis rate was not altered. No significant overshoot of anti-BSA-IgG beyond pre-removal levels occurred. Based on these findings it is postulated that an increase in antibody synthesis does not generally occur following plasma exchange. The rise in antibody levels seen following plasma exchange probably reflect a reduction of catabolism combined with an unchanged rate of synthesis.