Comparison of functional properties of thymic and splenic dendritic cells

Murine dendritic cells (DC) which are negative for surface immunoglobulin (sIg), Fc receptor (FcR), Thy-1 antigen, and the mononuclear phagocyte-specific marker F4/80, but positive for the DC-specific marker 33D1 and major histocompatibility complex (MHC) Class 1 and Class II antigens were obtained from either the spleen (SDC) or thymus (TDC) and used to stimulate alloreactive cytotoxic T lymphocyte (Tc) generation in vitro, in 5-day mixed lymphocyte reaction (MLR) to investigate some of their functional properties. SDC were potent stimulators of Tc cells in the absence of supernatant of concanavalin-A-stimulated spleen cells (CSS) and using medium containing 1% thioglycolate-stimulated mouse serum (TMS) to avoid potential artifactual helper T cell activation by fetal calf serum (FCS) antigens. TDC did not stimulate Tc cells under these conditions, but did so when mixed with small numbers of SDC, or in the presence of CSS. 33D1 and complement (C')-treated SDC and TDC populations failed to stimulate Tc cell responses in the absence of CSS. In the presence of CSS, TDC treated in a similar manner did not stimulate Tc cell activity, while 33D1 and C'-treated SDC stimulated a weak but detectable Tc cell response. These results indicate that genuine DC were the dominant cells presenting Class I MHC antigens in the TDC population and also that a minority of contaminating non-DC in the SDC population expressed sufficient MHC Class I antigens for Tc cell activation, but did not produce factor(s) required for Tc cell activation. The pretreatment of SDC and TDC with CSS before using them as stimulators did not improve their ability to stimulate Tc cell responses, indicating that the effect of CSS in improving the ability of TDC to stimulate Tc cell responses was not solely due to MHC-elevating effects of components of CSS. Lipopolysaccharide (LPS)-treated SDC synthesized abundant interleukin 1 (IL-1), but TDC synthesized low levels of IL-1. Contact for 24 hr between TDC and splenic Tc cell precursors in medium containing 1% TMS but without CSS and FCS did not tolerize the T cells.