TRANSFORMING GROWTH FACTOR-BETA-1 ENHANCES IGG AND IGA SHEEP RED-BLOOD-CELL RESPONSES

Antibody responses to ingested antigens can be inhibited by a mechanism known as oral tolerance which acts to prevent excessive stimulation from luminal contents. Local IgA responses can be induced in this non-responsive environment and during intestinal inflammation, mucosal IgG responses can also be increased. The purpose of this study was to compare a panel of cytokines to factors from macrophage - T cell co-culture supernatants for their ability to enhance isotype and sheep red blood cell (SRBC)-specific plaque-forming cell responses in an in vitro model of oral tolerance. IL-2, IL-4, IL-5, and IL-6, which have been implicated in IgA regulation of lipopolysaccharide-stimulated B cells, were not capable of enhancing responses in tolerized cultures; however, transforming growth factor (TGF)-beta1 had a dose-dependent ability to enhance responses to the T cell-dependent antigen SRBCs in this system. The enhancement was only seen when antigen was present and was neutralized by specific rabbit antiserum but not normal rabbit IgG. Similar treatment of soluble factors f rom the macrophage - T cell co-cultures did not inhibit their ability to enhance responses suggesting at least two distinct molecular mechanisms could augment responses in tolerized cultures. This was substantiated further by showing that TGF-beta1 was not isotype-specific. In contrast, adsorption of the macrophage - T cell co-culture supernatants against monoclonal IgA or IgG removed isotype-specific binding factors which were necessary for the enhancement of IgA and IgG respectively. The cellular target of TGF-beta in our cultures was the CD8+ suppressor T cells and examination of the kinetics showed TGF-beta1 took 2 - 3 days to manifest its activity but was rapidly reversible. Together, these data suggest that TGF-beta1 can enhance antigen-driven antibody responses and therefore may contribute to altered responses in inflammation.