The Attachment of IgG to Cell Components: A Reconsideration of Brambell's Receptor Hypothesis of Protein Transmission

Nuclear, mitochondrial and microsomal fractions were prepared from rabbit yolk-sac splanchnopleur and rabbit chorio-allantoic placenta, and tested in vivo and in vitro for attachment of labelled rabbit and bovine IgG. Similar fractions were prepared from small intestinal scrapings of neonatal rats, and tested in vivo and in vitro for attachment of labelled rat and sheep IgG. In all cases the attachment of the homologous and heterologous proteins was substantially equal. Digestion experiments on the labelled organelle pellets of rabbit yolk-sac were carried out with the proteases of the macerated tissue (the cell sap or final supernatant) at optimum pH. The nuclear pellet gave rise to a higher proportion of breakdown products derived from bovine than from rabbit IgG, showing the existence of a mechanism whereby selection between the two proteins might be brought about.