THE SPLENIC MARGINAL ZONE IS ABSENT IN ALYMPHOPLASTIC ALY MUTANT MICE

aly is a unique spontaneous autosomal recessive mutation in mice that causes a deficiency in the systemic lymph nodes (LN) and Peyer's patch es (PP). aly also induces abnormal histological findings in the spleen and a deficiency in humoral and cell-mediated immune functions, altho ugh lymphocytes of the aly/aly mouse show virtually normal immune resp onses in vitro. We studied the structure of the spleen of aly mice in detail by immunohistochemistry and electron microscopy. We fond that t he spleen of the aly/aly mouse was deficient in the expression of spec ific antigens for marginal metallophils (MM), marginal zone macrophage s (MZM) and fibroblastic reticular cells (FRC), which are components o f the marginal zone (MZ) of the spleen. Morphological analysis indicat ed that the aly/aly spleen is deficient in the structure of MZ, which may, in part, account for the severe immunodeficiency in the aly/aly m ouse. We then performed reciprocal bone marrow transplantation experim ents (BMT) between normal and aly mice and found a clear correlation b etween the formation of LN and the development of the splenic MZ in th ese mice; i.e. successful development of LN was invariably associated with the appearance of the MZ structure, whereas the failure of LN dev elopment was always associated with the absence of the development of MZ. These BMT results suggest that a common factor may regulate the ge neration of both LN and MZ of the spleen.