PERFORIN EXPRESSION IN LYMPHOCYTES INFILTRATED TO HUMAN COLORECTAL-CANCER

Perforin (PFP) is a cytotoxic protein released from killer cells. PFP immunoreactivity in human peripheral blood lymphocytes (PBL) and tumour infiltrating lymphocytes (TIL) was investigated immunocytochemically with the aid of an anti-PFP monoclonal antibody. PFP was detected in the cytoplasm of 10% of PBL. We performed a double staining of PFP + cells with Leu11b/CD16, Leu2a/CD8, or Leu3a/CD4 and showed that PFP was produced by 9% of CD8 + cells and 18% of CD16 + cells but not by CD4 + cells. In 28 colorectal cancer tissues, PFP immunoreactivity was observed in the lymphocytes infiltrating to the tumour stroma. The PFP + cells were most numerous in Dukes A and decreased in number according to the progression of tumours. The PFP + cells in TIL exhibited the same phenotypes as those in PBL but the PFP + cells were more numerous in CD8 + cells than in CD16 + cells at all stages. This study represents the first evidence that PFP is mainly secreted from CD8 + cells in tumour tissues. It is hypothesised that the decrease in the number of PFP + cells in accordance with tumour progression may reflect the suppression of the host's local immunity.