Antigen processing: cultured lymph-borne dendritic cells can process and present native protein antigens

Langerhans' cells (LC) cultured for 1-3 days lose their ability to process native protein antigens but acquire the ability to stimulate resting T cells as assessed in an allogeneic mixed lymphocyte response (MLR). Lymph-borne dendritic cells (L-DC) are physiologically involved in the transport of antigens to lymph nodes but it is not known whether these cells lose the ability to process antigens in culture. To investigate this, we cultured L-DC derived from the intestine for 20-72 hr and tested their ability to process and present antigens. Our results show that these L-DC are able to present antigen to primed spleen T cells as effectively as fresh cells. To exclude the possibility that commercial ovalbumin (OVA) preparations contain peptides which might bind directly to major histocompatibility complex (MHC) molecules, OVA was filtered through Sephadex G50 and the peak fractions used as antigen. The results show that cultured L-DC are also able to present G50-filtered OVA efficiently to primed spleen T cells. More importantly, these G50-OVA-pulsed L-DC are able to prime naive T cells specifically in vivo. Chloroquine inhibited the ability of both fresh and cultured L-DC to present antigen to primed T cells but did not inhibit their ability to stimulate a MLR, indicating that processing was a necessary step for antigen presentation. Taken together, these results clearly show that cultured L-DC are active in processing and presenting native antigens and the hypothesis proposed for LC does not apply to rat lymph-borne dendritic cells. The physiological significance of these observations is discussed.