IGE RECEPTORS, IGE CONTENT AND SECRETORY RESPONSE OF MAST-CELLS IN ATHYMIC RATS

Athymic, nude (Lewis rnu/rnu) and normal (Lewis +/+) rats were used to study the T-cell dependence of the regulation of IgE receptors and Ig E content on mast cells in vivo. We estimated the number of IgE recept ors and the IgE content on peritoneal mast cells using a cytofluoromet ric technique. The secretory capacity of the mast cells was measured i n terms of histamine release as a function of anti-IgE concentration b y incubation with antibodies in vitro. Two groups of rats, aged 6 and 13 weeks, were examined. The mast cells of the rats belonging to the o lder age group (both normal and athymic) had a higher total protein (e quivalent to dry mass or size) and mediator content (heparin, histamin e and 5-hydroxytryptamine) in accordance with previous findings. Mast cells of the athymic rats of both age groups contained similar levels of IgE receptors and IgE and did not differ in these respects from tho se of the normal rats. Of the IgE receptors available for binding, abo ut 80% were occupied by IgE in mast cells of normal and of athymic rat s in both age groups. The anti-IgE-induced histamine release of the ma st cells was, however, significantly lower in athymic rats compared to the normal controls. A change in housing from barrier-maintained to c onventional conditions for 2 weeks enhanced the IgE-receptor and IgE c ontent, as well as the releasability of histamine of the mast cells of both athymic and normal rats. The basal level of IgE occupancy of the receptors on mast cells was therefore not impaired in the athymic rat s, as might be inferred from previous findings of a T-cell dependence of the IgE immune response. The results further indicate that T-lympho cyte-derived cytokines appear not to be required for either the expres sion of IgE receptors or for their ability to acquire IgE on mast cell s, but such factors seem to enhance the release of histamine following the cross-linkage of the IgE receptor on mast cells in normal conditi ons.