Human albumin-induced granuloma studied by fluorescent antibody techniques

The fate of human albumin introduced into the skin of rats and the local immunologic responses were studied using fluorescein-antialbumin and rhodamine-albumin conjugates. Alum-precipitated human albumin injected into subcutaneous tissues of 30 rats was detected locally in the extra-cellular space and in the macrophages until the 16th day. Albumin was observed in the macrophages (cytoplasm and in some nuclei) from the fifth post-injection day. Plasma-cell aggregates appeared locally around blood vessels and, in addition, with macrophages and lymphocytes they formed structures reminiscent of lymph follicles. The term "immunofollicle" is suggested for the latter structures. It is reasonable to postulate that antibodies to the introduced antigen (albumin) may be produced in these immunofollicles-the site of antigen injection.