Antibody, antigen, and glomerular capillary wall charge interactions: Influence of antigen location on in situ immune complex formation. These studies examined the charge interactions between the glomerular capillary wall, antibody and antigen at different sites in the glomerulus. Sheep IgG was separated into differently charged subclasses and immunologically placed in one of two glomerular locations (subepithelial or subendothelial) to serve as planted antigen. Single kidneys with planted antigen were transplanted into uninephrectomized recipients that received affinity-purified, cationic and anionic rat anti-sheep IgG labelled with ¹²⁵I and ¹³¹I, respectively. Glomerular bound antibody was determined and corrected for antibody delivery. Specificity of antibody binding was confirmed by comparison of kidneys with or without planted antigen. The results indicate that the influence of charge on glomerular antibody binding depends on the site of the antigen. When antigen was planted in the subepithelial space, significantly more (15 to 25%) cationic than anionic antibody bound despite the fact that the antigen was cationic. Conversely, when the antigen was planted subendothelially, significantly more anionic (13 to 22%) antibody bound when the antigen was cationic, and significantly more cationic (7 to 16%) antibody bound when the antigen was anionic. Thus, the negatively-charged glomerular filtration barrier retards the permeation of anionic antibodies that complex with antigens located in the subepithelial space, but antigen-antibody charge interactions appear to predominate when the antigen is more proximally located.