Antibodies (Abs) specific to cell-surface receptors are attractive tools for studying the physiological role of such receptors or for controlling their activity. We sought to obtain such antibodies against the type 1 receptor for melatonin (MT 1 ). For this, we injected mice with CHO cells transfected with a plasmid encoding human MT 1 (CHO-MT 1 -h), in the presence or absence of an adjuvant mixture containing Alum and CpG1018. As we previously observed that the immune response to a protein antigen is increased when it is coupled to a fusion protein, called ZZTat101, we also investigated if the association of ZZTat101 with CHO-MT 1 -h cells provides an immunogenic advantage. We measured similar levels of anti-CHO and anti-MT 1 -h Ab responses in animals injected with either CHO-MT 1 -h cells or ZZTat101/CHO-MT 1 -h cells, with or without adjuvant, indicating that neither the adjuvant mixture nor ZZTat101 increased the anti-cell immune response. Then, we investigated whether the antisera also recognized murine MT 1 (MT 1 -m). Using cloned CHO cells transfected with a plasmid encoding MT 1 -m, we found that antisera raised against CHO-MT 1 -h cells also bound the mouse receptor. Altogether our studies indicate that immunizing approaches based on MT 1 -h-expressing CHO cells allow the production of polyclonal antibodies against MT1 receptors of different origins. This paves the way to preparation of MT 1 -specific monoclonal antibodies. [ABSTRACT FROM AUTHOR]