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

Splenectomy (Sx) has been proposed to attenuate post-PE (plasma exchange) rebound of isoagglutinins and xenogenic (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 unanesthetized, unheparinized rats. Immunoglobulin isotypes and subclasses (IgM, IgG1, IgG2 alpha, 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 XG 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 (mean +/- 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) Six 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.