Induction of an auto-anti-IgE response in rats. II. Effects on mast cell populations

Immunization of rats with purified rat IgE myeloma (IR2) induces an IgG class autoantibody directed specifically against the IgE isotype. This has variable stimulatory effects on the serum IgE concentration in high IgE-producing BN rats but significantly decreases the serum IgE concentration in the conventional PVG.RT1u strain. We have examined the effects of inducing such an auto-anti-epsilon response on mast cell populations, as defined by their staining characteristics in BN rats. A persistent anti-epsilon response changed the proportions of mast cell types. Those containing highly sulfated, Safranin-positive granules which equate with cells described as connective tissue mast cells (CTMC) were reduced in number in skin, tongue and bone marrow, whereas the less highly sulfated, Alcian Blue-positive mast cells were increased in number in these tissues as well as in the gut, a site rich in the so-called mucosal mast cell. The overall number of mast cells in nonmucosal sites was not significantly changed in anti-IgE-producing rats. The direct effects of anti-epsilon antiserum on mast cells in vivo were investigated using an immediate skin response (ISR) technique. The IgG component of serum from IR2-immunized rats, fractionated by high performance liquid chromatography or eluted from Sepharose 4B-coupled IR2, gave positive ISR in naive rats. The ISR was inhibited by prior incubation of immuno-purified rat anti-IR2 with solid-phase IR2 or with two unrelated IgE myeloma proteins but not with rat IgG. Histological examination confirmed that degranulation of CTMC had occurred at the ISR sites.