Site of Catabolism of Autologous and Heterologous IgA in Non‐Human Primates

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Abstract
Because of similarities between the human and monkey immune systems, we considered the monkey a suitable model for studies on the catabolism of various molecular forms of IgA, for which little information is available. The residualizing label dilactilol-[125I]tyramine was coupled to monkey (Macaca fuscata) IgA and IgG, as well as to human monomeric and polymeric myeloma IgA1 and IgA2 proteins. When labelled proteins were injected intravenously into monkeys, the non-metabolizable radioiodinated tracer accumulated at the cellular site of protein degradation, allowing identification of the catabolic sites. To determine the uptake or injected proteins by various tissues, monkeys were sacrificed 6-7 days after injection of labelled proteins, when blood-associated radioactivity was ≥ 10% of the injected dose, as measured by plasma clearance. When monkey or human monomeric IgA. as well as human polymeric IgA, irrespective of subclass, was administered to monkeys, the liver showed the greatest tissue uptake relative to total dose injected and to organ weight, and the highest acid soluble radioactivity (degraded protein). Although both hepatocytes and non-parenchymal liver cells were involved in IgA uptake, the hepatocytes were more active. Therefore, it appears that the liver is the major site of uptake and catabolism of IgA in monkeys and possibly in humans.