Preformed antibody and complement rebound after plasma exchange: analysis of immunoglobulin isotypes and effect of splenectomy

Abstract

Splenecomy (Sx) has been proposed to attenuate post-PE (plasma exchange) rebound of isoagglutinins and xenogeneic (XG) antibody (Ab) in both ABO-incompatible allografts and discordant xenografts. This study analyses the qualitative nature and kinetics of serum immunoglobulins as well as complement resynthesis after PE in sham-operated (PE) and splenectomized (PE + Sx) syngeneic LOU/ C rats; non-PE sham-operated or splenectomized animals were used as controls. PE was performed in unanaesthetized, unheparized rats. Immunoglobulin isotypes and subclasses (IgM, IgG1, IgG2a, IgG2b) of total circulating Ab were measured pre-PE and up to 21 days post-PE, using ELISA (enzyme-linked immunosorbent assay) and specific mouse antirat monoclonal Ab. Antiguinea-pig (GP) XG Ab (IgM, IgG2a) serum levels were measured using cellular ELISA with cultured GP endothelial cells as targets. Sx alone significantly reduced XG IgM serum levels ( p<0.0001). Maximal rebound of total and XG IgM was observed on day 3 post-PE, reaching 674% and 187% of the pre-PE levels, respectively; these overshoots were entirely suppressed by Sx ( p<0.005 for total IgM; p<0.0001 for ZG IgM). Total IgG2a, IgG2b and IgG1 as well as XG IgG2a serum levels did not show significant overshoot post-PE. The activity of the complement classical pathway (ean ± SD), assessed by CH50, was decreased at 51 ± 19% of basal value 15 minutes after PE, and had returned to baseline level by day 2 post-PE with or without Sx. In conclusion: (1) Sx alone significantly reduced XG IgM serum levels; (2) early post-PE Ab rebound was mainly observed for IgM; (3) both total and XG IgM rebound was inhibited by Sx. This suggests that Sx probably removes a significant proportion of IgM producing cells undergoing post-PE stimulation. These data provide a rationale for combining PE with Sx in ABO-incompatible and discordant XG transplantation.