Immunogenicity of the non-MHC-encoded endothelial antigen Eag-1 in various tissues of the rat.

Immunizations of MAXX rats with spleen and lymph node cells from BN donors lead to the production of antibodies against the renal endothelial antigen Eag-1. In the present study we analyzed the ability of various tissues to induce a response against Eag-1. Lung homogenates, like spleen and lymph node cells, induced a strong and rapid antibody response. A weak and slow response was induced by cardiac allografts as well as kidneys transplanted into recipients in which unilateral or delayed bilateral nephrectomy was performed. Transplantation of kidney or skin allografts into intact recipients did not result in the formation of Eag-1 antibodies, nor did immunizations with kidney homogenates. A rapid response, however, was observed after transplantation of BN kidneys into MAXX rats previously sensitized by a single injection of BN lymphoid cells, whereas no secondary response was induced by BN kidney homogenates. With an indirect immunofluorescence technique, Eag-1 was detected on lung and kidney endothelium, but not on lymphoid cells or heart and skin tissue. It thus appears that the immunogenicity of Eag-1 does not correlate with the quantitative expression in different tissues and that lymphoid cells, rather than vascular endothelial cells, can induce a strong and rapid response against Eag-1. Because the immunogenicity of lymphoid cells was diminished by heat treatment and freeze-thaw lysis, it appears that intact donor cells are required for the stimulation of antibody production.