Distribution and immunoregulatory properties of antisecretory factor.

Inflammatory processes and the mechanisms by which they are initiated and controlled within the central nervous system (CNS) involve a vast array of cell types and molecules. One cell type believed to be involved in the control of inflammation in the CNS is the microglial cell. The TLD antibodies are a panel of monoclonal antibodies reactive to rat microglial antigens. One antibody from this panel, clone TLD-1A8A, is specific for antisecretory factor (ASF). ASF is a previously identified protein characterized as a potent inhibitor of enterotoxin-induced intestinal fluid secretion. Our results extend the function of this molecule to include the regulation of immune reactions. Administration of TLD-1A8A to T-cell proliferation or mixed leukocyte response assays resulted in increased proliferation of T cells. Flow cytometric analysis indicates that ASF is expressed on macrophages, B cells and dendritic cells, but not on T cells or granulocytes. Immunohistochemical analysis indicates that ASF is expressed by macrophages and cells of dendritic morphology in the spleen, thymus, lymph nodes, Peyer's patch, and in the perivascular area in the CNS. Furthermore, Western blot analysis indicates that ASF is expressed in many tissues including all secondary lymphoid organs. These data suggest that ASF may have a previously unsuspected role in regulating the immune system.