Enhancing Activity of Thymocyte Culture Cell-Free Medium on the <i>in vitro</i> Immune Response of Spleen Cells from Neonatally Thymectomized Mice to Sheep RBC

Abstract Peripheral lymphoid tissues are made up of mixed populations of thymus-dependent and thymus-independent lymphocytes. In the mouse immunized with sheep red blood cells (RBC), specific antibodies are produced by thymus-independent cells upon interaction with thymus-dependent cells and the antigen (1). The nature of this interaction is not understood, but several mechanisms have been proposed (2). Our previous studies (3) have shown that cooperation between thymocytes from normal mice and splenocytes from neonatally thymectomized mice or from thymectomized chimeras (mice thymectomized in adult life, lethally irradiated, and grafted with isogenic bone marrow cells) can occur in vitro, because a primary immune response could be induced in vitro only if both the thymocytes and thymus-independent cells were cultured with sheep RBC. This in vitro system was used to investigate whether receptor sites are involved in the cooperation between thymocytes and splenocytes from neonatally thymectomized mice. It was found that thymocytes lack demonstrable receptor molecules, such as those detected on thymus-independent cells and present in normal serum, for thymocytes were not prevented by rabbit antibodies to mouse whole serum from interacting with antigen and thymus-independent cells (4).