In this study, Lym-1, a murine IgG2a monoclonal antibody that recognizes a polymorphic variant of HLA-DR antigens present on malignant B cells that has been given intravenously in previous clinical trials, achieved lymphoma cell lysis in the presence of C5a, whereas C5a-deficient human serum did not promote Lym-1 antibody-dependent lysis [13,24]. This evidence concerns the gene C5AR1 and lymphoma.