Thymus Dependence of the Spontaneous Induction of the in Vitro Anamnestic Antibody Responses to Human Serum Albumin and Keyhole Limpet Hemocyanin

Abstract

Abstract Recently we reported that IgG antibody synthesis was spontaneously induced—no extrinsic antigen required—simply by transferring lymphoid cells from a human serum albumin (HSA)3 immunized rabbit into cell culture (1). Initiation of this spontaneous in vitro response was attributed to cell-associated persisting antigen, whose immunogenicity was subject to an antibody feedback mechanism (1). It was proposed that this in vitro phenomenon represented the essential features of the mechanism whereby antibody synthesis is maintained and regulated in vivo for months or years after antigen injection (1). Subsequently, additional evidence was presented that: a) persisting antigen was responsible for induction of the spontaneous antibody response, and b) this persisting antigen was bound to the surface of an accessory cell such as a sessile macrophage or dendritic type cell (2). The purpose of the present study was to determine whether thymus-derived (T) lymphocytes were required for the induction of the spontaneous antibody synthesis. The determination of the role of T lymphocytes was made with the aid of an IgG fraction of a goat anti-rabbit thymocyte serum (ATG). Several studies have provided a great deal of diverse evidence for the specificity of this serum for rabbit T lymphocytes (3=-5) and for its lack of cytotoxicity for rabbit lymph node lymphocytes both in the presence and absence of complement (4). The current experiments utilized the described spontaneous response to HSA as well as this type of response to keyhole limpet hemocyanin (KLH) because it had been shown that induction of the in vitro anamnestic IgG antibody responses to HSA (Stavitsky, A. B. and Tew, J. G., unpublished observations) and KLH (4) by added antigen required T lymphocytes.