Effect of prolactin on carcinoembryonic antigen‐specific cytotoxic T lymphocyte response induced by dendritic cells
The cytokine hormone prolactin (PRL) has been shown previously to modulate native cellular responses and maturation of antigen‐presenting cells. Here we have addressed its effect on the antigen‐specific response of cytotoxic T lymphocytes (CTL). CTL were generated from HLA‐A2 lymphocytes after three rounds of stimulation with autologous dendritic cells loaded with HLA‐A2‐restricted carcinoembrionic antigen (CEA) Cap‐1 (YLSGANLNL) peptide. Selected cultures were expanded on cytokine‐supplemented feeder‐layers, enriched for CD8+ lymphocytes and analysed for PRL‐receptor (PRL‐R) expression and PRL responsiveness. Resting CD8+ lymphocytes were negative for PRL‐R, whereas antigen‐activated CD8+ lymphocytes derived from long‐term cultures were highly positive. Results of a 51Cr release assay showed CTL killing of CEA‐loaded, but not unloaded, T2 cell line and the CEA‐positive gastric carcinoma cell line KATO, but not of the CEA‐negative T leukaemia cell line Jurkat. Interferon (IFN)‐γ release, evaluated in an ELISPOT assay against CEA‐loaded T2, was enhanced (P < 0·05) by concentrations of PRL (12–25 ng/ml) very close to the physiological levels (6–20 ng/ml), but was decreased (P < 0·05) by high concentrations (200 ng/ml). Pre‐incubation of the stimulators with the anti‐MHC class I MoAb W6·32 induced a 40–60% decrease of the PRL‐boosted IFN‐γ release, thus proving the MHC restriction of the lymphocyte response. Cytotoxicity against CEA‐loaded T2 and KATO cell lines was also increased by 12–25 ng (P < 0·05) and decreased (P < 0·05) by 200 ng PRL. Pre‐incubation of CTL with an antibody specific for the PRL‐R almost completely abrogated this effect.