Abnormal organisation of the splenic marginal zone and the correlated leukocytosis in lymphotoxin-alpha and tumor necrosis factor alpha double deficient mice.

In this study we further characterized the phenotype at the homeostasis of mice genetically deficient in Tumor Necrosis Factor-alpha and Lymphotoxin-alpha (LT-alpha TNF-alpha -/-). As initially observed in LT-alpha -/- mice, these mice are devoid of lymph nodes and Peyer's patches, while in their spleen the white and red pulp domains are no more detectable. In the blood the leukocytosis dominated by lymphocytosis is not solely due to the absence of lymph nodes. Indeed, this abnormality was shown to be correctable by the transfer of wild type bone marrow in the absence of lymph node. We now report that the metallophilic macrophages of the marginal zone are no more detectable with an antibody reactive to sialoadhesin, a macrophage restricted transmembrane molecule known to bind myeloid and lymphoid cells. The absence of sialoadhesin within the marginal zone, a critical domain for lymphocyte trafficking towards the white pulp suggests a possible cellular basis for the observed blood leukocytosis. In addition, in the peritoneal cavity of LT-alpha TNF-alpha-/- mice, the size of the resident leukocyte population is increased. By their amplitudes these leukocytosis are similar within the blood and the peritoneal compartments.