The localization of immunoglobulin and immune complexes in lymphoid tissue.

Aggregated and monomeric forms of human γ-globulin (HGG) were prepared by heating at 63°, ultracentrifugation and subsequent separation according to solubility in 0.62 M sodium sulphate. These two forms were injected intradermally into guinea-pigs' ears and their distribution in the draining auricular nodes determined at different times following injection by staining cryostat sections with fluorescein labelled anti-HGG. Monomeric HGG showed no precise localization; aggregated HGG localized rapidly in the phagocytic macrophages of the sinuses and medulla and after a few hours' delay in the germinal centres in a dendritic pattern, the latter persisting for up to 4 weeks. With doses of less than 10 μg, aggregated HGG was not seen in the medulla but germinal centre staining was readily visible, possibly due to a concentrating effect. Prior injection of a large dose of monomer either locally or systemically did not alter the pattern of staining produced by subsequent injection of aggregated HGG. Aggregated human serum albumin, colloidal carbon and streptococcal cell walls did not localize in germinal centres in the same way. Monomeric rabbit IgG anti-HSA injected alone did not localize, but when combined with HSA in antigen excess to form soluble immune complexes it localized in germinal centres. It is concluded that germinal centres contain receptors, probably at cell surfaces, for IgG aggregated by mild heat or by complexing with antigen but not for unaltered native IgG, and it is suggested that this may be a means of disposal of aggregated or complexed IgG.